Thermalyze Operation

Overview

Description

Lock-in thermography (LIT) is a process of automatically and repeatedly powering an electronic device at regular intervals while thermal images of the device are analyzed by software.  The following description is over simplified but helps to provide a basic understanding of the Lock-in Thermography process.

Over many power cycles, thermal images captured while the device is powered are added together.  Likewise, thermal images capture while the device is unpowered are added together.  The unpowered sum is subtracted from the powered sum resulting in a Lock-in image that represents temperature differences between the powered and unpowered state.  As the LIT test continues, more and more thermal images are added together, resulting in a Lock-in image with higher and higher sensitivity.  In fact, test sensitivity is inversely proportional to the square root of the number of images captured during a lock-in test.  Typically, a lock-in test is allowed to run until the fail site is detected and can be precisely located.  In many cases, a temperature increases less than 1 mK (0.001°C) and power dissipation below 10 microW can often be detected.

Device power can be applied at a Cycle Frequency of up to 15 Hz.  Performing LIT tests at lower frequencies improves test signal/noise due to higher device heatup.  Higher frequency tests improve hot spot spatial resolution by reducing thermal diffusion into adjacent areas of the device.

Figure 1: Lock-in thermography

Device Powering

Device biasing is accomplished via exposed leads, package pins, or by probing the device.  One or more of the biasing leads are routed through the relay(s) in the Relay device so that the software can control the timing of applied power.  The applied voltage and current levels are initially set low to prevent altering the defect characteristics or damaging the device.

Lock-in Images

A number of useful images can be calculated and displayed including an amplitude image, single phase image, phase image, and cycle image.  Each Lock-in image type has a specific use in locating defect xy position, locating defect depth, or analyzing heat flow.

Amplitude Image

An amplitude image displays all temperature increases on a device at any time during the cycle and is commonly used to determine fault location in the xy direction.

Single Phase Image

A single phase image displays temperature changes at specific times within the cycle.  The time within the cycle can be expressed as a phase angle with 0 degrees representing the beginning of the cycle when a device is powered and -180 degrees representing when power is removed.  A phase angle of -360 degrees represents the end of the cycle and is equivalent to a phase angle of 0 degrees.  Single phase images are is used to locate faults in the xy direction.  They can also identify areas that heat up at different times within the cycle providing a correlation with defect depth.  Single phase images typically produce the highest xy spatial resolution of all Lock-in images.

Phase Image

A phase image displays the phase angle of heating at each point in the image.  Phase angle is most often associated with defect depth because heating phase angle represents the time within a cycle when internally generated heat reaches the surface.  Phase angle represents the delay between powering a device and the resulting surface heating.  When analyzing packaged devices and stacked die, phase angle is used to estimate the depth of a defect.

Cycle Image

A cycle image displays device heating at a specific time during a cycle.  Cycle images are useful for visualizing heat flow across a device.

Window

Description

The Lock-in Thermography (LIT) window (see Figure 2) enables the detection and location of very small temperature heating (below 0.001°C) associated with leakage current and short circuits on electronic devices.  To open this window, click the Lock-in Thermography item under the Testing menu or press the  button in the Testing section of the Shortcuts toolbar.

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Figure 2: Lock-in Thermography window

Test Files

The following data is saved when a lock-in test is saved.  Test data including Date/Time, Completed Cycles, Accepted Images, Rejected Images, Cycle Data, and History Image are saved in a binary file with .olit extension.  Lock-in Settings are saved in an ASCII text file with .oset extension located in a folder with the same name as the test data file.

Date/Time	The date and time when the file was saved.
Completed Cycles	The number of cycles that were completed during the test.
Accepted Images	The number of captured images that were not rejected by Image Rejection criteria.
Rejected Images	The number of captured images that were rejected by Image Rejection criteria.
Cycle Data	Captured image data that has been accepted during the test.
History Image	An average of recently captured images that is compared to each captured image to determine if it should be accepted or rejected.  The criteria used for the comparison are located in the Advanced Settings window.
Lock-in Settings	All settings accessible in the Lock-in Thermography, Test Setup, Relay Setup for Lock-in Thermograhpy Tests, Advanced Settings, and Phase Image windows.

File

Open Test	Select the LIT test file (.olit) to open.  When a lock-in test file is opened, the test file date/time is displayed at the bottom of the window. Note: The file name of the most recently opened or saved LIT test file is displayed at the bottom of the window.
Save Test	LIT test data is saved in binary format with a .olit extension.  LIT test settings are saved in ASCII text format with a .oset extension.  All of the data associated with a lock-in test are saved in the binary file and therefore, LIT tests can be opened at a later time for analysis and tests can even be continued.  LIT test files are approximately 150 MB in size. When saving a lock-in test, the file name that you provide is appended with ".olit" and saved in the "Optotherm\Thermalyze\LIT" folder, unless a different folder is selected.  LIT test settings are saved in a folder with the same name as the .olit file. Tip: It may be helpful to include the name of the currently installed camera lens in the file name so that when the file is opened at a later time, the lens used can be identified. Note: When overwriting an existing LIT test file, you must include the ".olit" extension in the name or else the existing test folder will be opened when the Save button is pressed.
Export Window	The Lock-in Thermography window can be saved to file in the following formats: bmp, jpg, png, and tif.  The size of the exported image is proportional to the size of the window. Note: Exported Lock-in Thermography windows are saved in the "Optotherm\Thermalyze\Export" folder unless you specify a different folder.
Print	Print the Lock-in Thermography window. Note: You must have a printer connected to your computer.
Print with Preview	Select this menu item to open the Print Preview dialog before printing.

Setup

Test Setup	Select this menu item to open the Test Setup window containing settings such as Cycle Frequency and Test Resolution.
Instrument Control	Select this menu item to open the Instrument Control window.  The instrument output is used to power devices during LIT tests using Keithley source measure units.
Relay Setup	Select this menu item to open the Relay Setup for Lock-in Thermography window.  The relay outputs are used to control power to devices while performing LIT.
Advanced Settings	Select this menu item to open the Advanced Settings window containing settings such as image stability, noise reduction, and image smoothing.
Large Image Size	Press this button to display the LIT image in full size, unpress for reduced size.

Show

Amplitude	Click this menu item to calculate and display the amplitude image.
Phase	Click this menu item to open the Phase Image window and display the phase image.
Single Phase	Click this menu item to calculate and display the single phase image at the phase angle selected.
Cycle Image	Click this menu item to calculate and display the cycle image at the image number selected.

Transfer

Lock-in images can be transferred to the Main Image and the cycle sequence can be transferred as an image sequence so that additional analysis tools can be used on the images, for example to graph region statistics or to view statistics from multiple Regions.

When Test Resolution is set to 10 microK, Lock-in images represent differential temperature images and therefore transferred Lock-in images are displayed with Image Subtraction activated to preserve 10 microK resolution.  When Test Resolution is set to 10 mK, Lock-in images represent temperature images and therefore transferred Lock-in images are not displayed with image subtraction activated.

Displayed Image	Click this menu item to transfer the currently displayed amplitude image, single phase image, or cycle image to the Main Image.
Thermal Overlay as Image	Click this menu item to calculate and transfer the thermal overlay image to the Main Image.  The thermal overlay's color palette can then be changed, and its contrast adjusted so that it can be used as an Overlay.
Thermal Overlay as Overlay	Click this menu item to calculate and transfer the thermal overlay image to the Overlay window where it can be used as the overlay for the Main Image.
Cycle Sequence	Click this menu item to transfer the entire sequence of cycle images to an image sequence.

Tools

Defect Depth Analysis

Click this menu item to open the Defect Depth Analysis window.

Zoom

Zoom In	Select this button and then click a point on the image to zoom in to that area.  Images can be zoomed from 1x up to 8x.  After zooming in to 8x, the Pan tool is automatically selected to allow you to pan the image.
Zoom Out	Select this button and click a point on the image to zoom out from that area.  After zooming out to 1x, the Pan button  is automatically selected.
Zoom Out Full	Click this button to zoom out to 1x.  After pressing this button, the Pan tool is automatically selected.
Zoom Level	This field display the current zoom level.
Pan	Select this button and then click and drag on the image to pan.  The image must be zoomed in at least 2x in order to pan.

Color Palette

Lock-in images are displayed using the same colors as the Spectrum Color Palette when Image Subtraction is activated, i.e., a gray area is added to Spectrum Palette between the green and blue colors and represents the temperature value of zero.

Auto	Click this button to set the Palette Max and Min values to the highest and lowest temperatures in the Lock-in image.  If the Auto Scale in Region box is check and a Region has been drawn on the Lock-in image, the Palette Max and Min values are set to the highest and lowest temperatures within the Region.
In	Click this button to zoom in to the Palette Max and Min slider scales in order to make fine adjustments.
Out	Click this button to zoom out of the Palette Max and Min slider scales in order to make course adjustments.
Auto Scale Each	When this box is checked, the color palette is automatically scaled each time the Lock-in image is updated and displayed.
Auto Scale Region	When this box is checked and a Region has been drawn on the Lock-in image, the Palette Max and Min values are set to the highest and lowest temperatures within the Region when the Auto button is clicked.
Palette Max, Min	Color palettes can be scaled within a specific temperature range by dragging the palette Max and Min sliders.  Adjust the sliders to improve the contrast of the image within the temperature range of interest. Tip: The palette sliders can also be adjusted using the mouse wheel and Ctrl key as explained in the Introduction. The palette temperature range, displayed to the right of the image, displays the temperatures represented by the individual colors of the current color palette.
Palette Max Value	Set or adjust the palette max value.
Palette Min Value	Set or adjust the palette min value.
Restore	Click this button to load the previously saved palette max and min values.
Set	Click this button to save the current Palette Max and Min values to memory as defaults.  The currently saved default values are displayed to the right of this button.

Testing

ON/OFF	Press this button to start/stop a lock-in test.
High Low	These indicator lights illuminate when a relay or instrument output is activated. Note: When Power Mode is set to Pulse and instrument Protocol is set to SCPI, the lights will illuminate during each pulse.  When Protocol is set to TSP, lights will illuminate only during the first half of each cycle.
Cycles	This field displays the number of cycles that have been completed in the current test.
Test Time	This field displays the time that has elapsed during the current test in hours, minutes, and seconds. Note: If images are rejected during a lock-in test, elapsed time will not correlate exactly with the number of cycles.
Lock-in Data	In order for a Lock-in image to be calculated, at least one complete cycle must be completed.  A completed cycle is indicated when this progress bar reaches 100%.
Clear Test	Click this button to clear all existing test data from memory in order to begin a new test.

Test Info

Init Cycles:	This field displays the number of initialization power cycles that have been performed at the start of a lock-in test.  The Cycle Initialization setting determines the number of power cycles that must be performed at the start of a test.
Accepted:	This field displays the number of captured images that have been accepted in the test based upon the Image Rejection criteria.
Rejected:	This field displays the number of captured images that have been rejected during the test based upon the Image Rejection criteria.
Noise (image):	This field displays the noise measured in the displayed Lock-in image.  By comparing the image noise to the theoretical noise, you can detect test degredation due to excessive thermal noise or acceptance of corrupt images.  If severe test degredation occurs, the test data should be cleared, and the test should be started again.
Noise (theory):	This field displays the theoritical noise level of the test which is inversely proportional to the square root of the number of images that have been accepted in the test.  As more images are accepted, theoretical noise level will decrease. Note: This value is a theoretical calculation of noise level based on camera detector sensitivity and image count.  It does not take into account other thermal noise sources from the ambient environment.

Update

Single Phase (option)	Choose this option to calculate and display the single phase image at a frequency determine by the Image Update Minimum setting.
Amplitude (option)	Choose this option to calculate and display the amplitude image at a frequency determine by the Image Update Minimum setting. Tip: Calculating amplitude images require approximately twice the processing power as single phase images.  To minimize delays in the acceptance of captured thermal images into a long-running LIT test, choose the Single Phase option.
Phase (checkbox)	Check this box to calculate and display the phase image at a frequency determine by the Image Update Minimum setting.  If the Phase Image window is closed, it will be opened when the phase image is updated. Tip: Calculating phase images require significant additional processing power and may cause delays in the acceptance of captured thermal images during a lock-in test.  Do not check this box unless the phase image must be updated at a frequency determine by the Image Update Minimum setting.  As an alternative, consider clicking the Phase button to update the phase image when required.
Amplitude (button)	Click this button to calculate and display the amplitude image.
Phase (button)	Click this button to calculate and display the phase image. Note: If closed, the Lock-in Phase Image window will open when this button is clicked.

Single Phase Image

There is a time delay between when power is applied to a device and when the internally generated heat diffuses through the device and reaches the surface.  The magnitude of this delay is dependent on the thermal conductance of the material in the device and the depth of the defect.  A single phase image displays temperature increases at a specific time in the cycle.  The time within the cycle can be expressed as a phase angle with 0 degrees representing the beginning of the cycle when a device is powered and -180 degrees representing when power is removed.  A phase angle of 360 degrees represents the end of the cycle and is equivalent to a phase angle of  0 degrees.  Single phase images are is used to locate faults in the xy direction.  They can also identify areas that heat up at different times within the cycle providing a correlation with defect depth.  Single phase images typically produce the highest xy spatial resolution of all Lock-in images

A single phase image with phase angle = 0 degrees displays device heating that occurs immediately after power is applied and can be used to identify faults or heating that takes place near the surface of the device.  A single phase image with a negative value of phase angle, such as -150 degrees, displays device heating that occurs at some time after power is applied and can be used to observe heating that occurs at a distance beneath the surface.  A single phase image at a larger negative phase angle displays heating occurring at greater depths.  A single phase image with phase angle = -360 degrees displays heating that occurs at a time delay equal to one complete cycle period and is equivalent to a single phase image with phase angle = 0 degrees.

The available phase angles depend on Cycle Frequency and are equally distributed within the range of 0 to -360 degrees.  The number of phase angle increments is determined by the following equation: Number Phase Increments = Camera Frame Rate / Test Cycle Frequency.  For example, the number of phase increments when Cycle Frequency is set to 5Hz = 60Hz / 5Hz = 12.  Dividing the range of 0 to -360 by 12 yields 30 degrees.  Therefore, the available phase angles are 0, -30, -60, -90, -120, -150. -180, -210, -240, -270, -300, -330, and -360 degrees.  Note that for Cycle Frequency of 1Hz and all value of Cycle Time, the number of phase angle increments is equal to 60.

Phase Angle	Drag the handle to change the phase angle of the single phase image to display.  Alternatively, you can hover over the trackbar and use the mouse scroll wheel to change the value. Note: A value of -360 degrees indicates for a time delay of one complete cycle period, resulting in a single phase image that is identical to a single phase image with phase angle = 0 degrees.
Show Single Phase	Click this button to calculate and display a single phase image at the phase angle selected.
<  >	Click these arrow buttons to select the next available phase angle to the left or right.

Overlay Merge

A thermal image or picture overlay can be merged with the Lock-in image to facilitate locating the xy coordinates of device heating.  A thermal overlay is a grayscale thermal image of the device and is created by averaging all of the captured images that have been accepted in the LIT test.  When thousands of images have been accepted, the thermal overlay image has very low noise level and provides a high resolution image for locating defects.  The grayscale color palette that is applied to the thermal overlay associates the black end of the palette to the lowest temperature in the thermal overlay image and the white end to the highest temperature.  A picture overlay is created using the Overlay window.  To merge the overlay with the Lock-in image, pixels in the Lock-in image with the highest values replace corresponding pixels in the overlay.  The temperature range of the replacement pixels is determined by the Range level.

Show	Check this box to calculate and display the merged overlay each time the Lock-in image is calculated and displayed. Tip: Calculating the thermal overlay requires significant additional processing power and may cause delays in the acceptance of captured thermal images during a lock-in test.  Do not check this box unless the thermal overlay must be updated at a frequency determine by the Image Update Minimum setting.  As an alternative, consider checking this box and displaying the thermal overlay at the end of the LIT test after localized heating has been detected.
Contrast	Check this box to enhance the thermal overlay contrast according to the Image Sectors and Histogram Limit settings in the Lock-in Advanced Settings window.
Picture	Check this box to create the merged overlay using the picture from the Overlay window.  Uncheck this box to create the thermal overlay.
Range	This setting determines the range of high-temperature pixels in the Lock-in image that replace corresponding pixels in the thermal overlay.  Drag the trackbar handle to change the value. Tip: You can also hover over the trackbar and use the mouse scroll wheel to change the value.
Refresh	Click this button to update the thermal overlay after changing the Range.
Scale	Click this button to open the Thermal Overlay Palette window.
Auto Scale	Click this button to automatically scale the thermal overlay.

Cycle Sequence

A cycle image displays device heating at a specific time during a cycle.  Cycle images are useful for visualizing heat flow across a device.  The number of cycle images available is equal to the number of images per cycle.  The number of images per cycle = Camera Frame Rate / Test Cycle Frequency.  For example, the number of images per cycle when Cycle Frequency is set to 5Hz = 60Hz / 5Hz = 12.  Note that the maximum possible number of image per cycle is equal to the the camera frame rate.

Image #	Drag the trackbar handle to select the cycle image to display. Tip: You can also hover over the trackbar and use the mouse scroll wheel to change the value.
Show	Click this button to calculate and display a cycle image at the image number selected.
<  >	Click these arrow buttons to select the next available cycle image to the left or right.

Cursor Info

Temp	This field displays the Lock-in image pixel value at the mouse cursor location.
Location	This field displays the xy coordinates at the mouse cursor location.

Region Tools

You can draw one Region of any shape or size on the Lock-in image in order to view maximum, minimum, and mean values of the pixels enclosed by the region.  When the Auto Scale Region box is checked, the Palette Max and Min values are set to the highest and lowest temperatures within the Region.

To help in locating heat sources on a device, the Region can be copied to/from the Main Image or the Phase Image.

Select	Select this button to position, resize, and rotate the Region.
Point	Select this button and then click on the image to create a Point Region.
Line	Select this button and then click and drag on the image to create a Line Region.
Rectangle	Select this button and then click and drag on the image to create a Rectangle Region.
Ellipse	Select this button and then click and drag on the image to create an Ellipse Region.
Polyline	Select this button and then click on the image to locate the first vertex of the Polyline Region.  Click to locate each vertex and then right-click on the last vertex to complete the polyline.
Polygon	Select this button and then click on the image to locate the first vertex of the Polygon Region.  Click to locate each vertex and then right-click on the last vertex to complete the polygon.
Delete Region	Click this button to delete the Region.

Invert Region Color	The default color of an unselected Region is white.  If the Region is difficult to distinguish from lite background colors, press this button to set the unselected Region color to black.
Show Scale Legend	Press this button to display a large cross hairs in the center of the lock-in image.
Show Center	Press this button to display a large cross hairs in the center of the lock-in image.
Measure	Press this button to display the Region Measure window.
Hot Spot Locator	Press this button to create a rotated rectangle region with a corner located on a reference point and the opposite corner located on the hot spot.  When pressed, step-by-step instructions to create the rectangle are display to the right of this button.  The first mouse click sets the reference point (e.g., feature corner).  The second click defines the reference edge (e.g., angle of feature edge).  Finally, click near the hot spot and the rectangle corner will snap to the hottest pixel within a radius defined by the Search Radius setting in the Measure Settings window.

Phase Image

Description

The Phase Image window (see Figure 3) displays the time delay between powering a device and subsequent heating on the surface of the device.  To open this window, click the Phase item under the Show menu (or click the Phase button in the Test Results panel) on the Lock-in Thermography window.

Figure 3: Phase Image window

Phase Angle

The phase image displays the phase angle of heating at each point in the image. Phase angle is most often associated with defect depth because heating phase angle represents the time within a cycle when internally generated heat reaches the surface. Phase angle represents the delay between powering a device and the resulting surface heating. When analyzing packaged devices and stacked die, phase angle is used to estimate the depth of a defect.

Phase angle is measured in units of degrees and has a range of 0 to -360 degrees. A phase angle of 0 degrees indicates device heating occurring immediately after power is applied and takes place at or near the surface. Negative phase angle values, such as -120 degrees, indicate device heating occurring at some time after power is applied and somewhat below the surface. Larger negative values of phase angle indicate heating occurring at even greater depths.  Phase angle is dependent on defect depth, on the thermal conductance of the materials comprising the device, and on Cycle Frequency.  Heat generated in devices with higher thermal conductivity will result in reduced time delays and lower magnitude phase angles.  As test frequency increases, time delay becomes a larger fraction of the total cycle time, resulting in a phase angle with larger magnitude.

The time required for internally generated heat to reach the device surface can be calculated according to the following equation: Time Delay = Phase Angle / 360 / Test Frequency.  For example, a Phase Angle of -60 degrees at a Test Frequence of 2.5 Hz indicates a Time Delay = -60 / 360 / 2.5 Hz = 67ms.

3D SIP Devices

Determining fault depth in 3 dimensional system-in-package (3D SiP) devices is becoming increasingly important due to their expanding complexity and decreasing dimensions. As the number of stacked die in 3D SiP devices grows, isolating the root cause of defects within the package becomes more challenging. Sentris provides a non-destructive technique to localize the depth of faults through 3D SiP packages.

Device Powering

Device biasing is accomplished via exposed leads, package pins, or by probing the device and software control of device power using direct Instrument control or Relays.  The applied voltage and current levels are initially set low to prevent altering the defect characteristics or damaging the device.  Also, large temperature changes within semiconductors can alter their thermal diffusion properties and modify the phase/depth relationship.

Many 3D SiP devices undergo an initialization process that is triggered at a specific voltage level.  If the applied voltage is cycled between 0 and a value above the initialization voltage level, the initialization process may cause non-defect related power dissipation that can interfere with detecting the true fail site.  In these cases, the device should be initialized before the Lock-in Thermography (LIT) test begins, and the applied voltage should be cycled between two voltages that are above the initialization voltage.

Additionally, some 3D SiP devices include on-chip voltage regulators and defect power dissipation may not correlate with on-off power cycling.  In such cases, the Lock-in relays can be used to trigger device test equipment in order to properly dias devices.

Calculating Fault Depth

By measuring the phase angle of one or more known reference heat sources inside a device, a relationship between phase angle and depth can be plotted (see Figure 4).  This plot can then be used to estimate the depth of unkown faults by comparing their phase angle to the plot.

The relationship between phase angle and fault depth is dependent on the test cycle frequency.  A suitable frequency should be selected that results in a high plot slope.  This will enable differentiation between die levels more easily.  First, a device is tested at a moderate frequency, such as 2.5 Hz.  Then, depending on the phase results, another test may be conducted at a higher or lower frequency.  If phase angles between 0 and -140 degrees are obtained at 2.5 Hz, for example, phase angles may be saturated at 0 degrees and the next test should be performed at a higher frequency, such as 3.75Hz.  On the other hand, if phase angles between -220 and -360 degrees are obtained at 2.5 Hz, phase angles may be saturated at -360 degrees and the next test should be performed at a lower frequency, such as 1.25Hz.  If phase angles between -140 and -220 degrees are obtained, the test frequency does not need to be changed.

To create a defect depth plot, the device must be tested by cycling power to at least one reference heat source whose depth is known.  Defective devices can be used by recording the phase angle of known faults at various depths.  Internal I/O diodes located on multiple die levels can also be used as reference heat sources by forward biasing them.

Figure 4: Plot of defect depth versus phase angle

File Menu

Export Window	The Phase Image window can be saved to file in the following formats: bmp, jpg, png, and tif.  The size of the exported image is proportional to the size of the window. Note: Exported Phase Image windows tests are saved in the "Optotherm\Thermalyze\Export" folder unless you specify a different folder.
Print	Print the Phase Image window. Note: You must have a printer connected to your computer.
Print with Preview	Select this menu item to open the Print Preview dialog before printing.

Setup

Large Image Size

The phase image can be displayed with a size of 640 x 480 or 1280 x 960 pixels.  Press this button to display the phase image size in 1280 x 960.

Zoom

Zoom In	Select this button and then click a point on the image to zoom in to that area.  Images can be zoomed from 1x up to 8x.  After zooming in to 8x, the Pan tool is automatically selected to allow you to pan the image.
Zoom Out	Select this button and click a point on the image to zoom out from that area.  After zooming out to 1x, the Pan button  is automatically selected.
Zoom Out Full	Click this button to zoom out to 1x.  After pressing this button, the Pan tool is automatically selected.
Zoom Level	This field display the current zoom level.
Pan	Select this button and then click and drag on the image to pan.  The image must be zoomed in at least 2x in order to pan.

Color Palette

Phase images are displayed using the same colors as the Spectrum Color Palette when Image Subtraction is activated, i.e., a gray area is added to Spectrum Palette between the green and blue colors and represents the temperature value of zero.  The units for phase angle are degrees and the scale range is -360 to 0 degrees.

Auto	Click this button to set the Palette Max and Min values to the highest and lowest phase angles in the phase image.  If the Auto Scale in Region box is check and a Region has been drawn on the phase image, the Palette Max and Min values are set to the highest and lowest phase angles within the Region.
In	Click this button to zoom in to the Palette Max and Min slider scales in order to make fine adjustments.
Out	Click this button to zoom out of the Palette Max and Min slider scales in order to make course adjustments.
Auto Scale Each	When this box is checked, the color palette is automatically scaled each time the phase image is updated and displayed.
Auto Scale Region	When this box is checked and a Region has been drawn on the phase image, the Palette Max and Min values are set to the highest and lowest phase angles within the Region when the Auto button is clicked.
Palette Max, Min	Color palettes can be scaled within a specific phase angle range by dragging the palette Max and Min sliders.  Adjust the sliders to improve the contrast of the image within the phase angle range of interest. Tip: The palette sliders can also be adjusted using the mouse wheel and [Ctrl] key as explained in the Introduction. The palette phase angle range, displayed to the right of the image, displays the phase angles represented by the individual colors of the current color palette.
Palette Max Value	Set or adjust the palette max value.
Palette Min Value	Set or adjust the palette min value.
Restore	Click this button to load the previously saved palette max and min values.
Set	Click this button to save the current Palette Max and Min values to memory as defaults.  The currently saved default values are displayed to the right of this button.

Phase Offset

When plotting multiple phase/depth relationships on a device, it may be helpful to zero the phase of a heat source at a specific depth.  This can simplify the depth calculations of other heat sources on the device.  To zero the phase, enter a Phase Offset value that results in a phase value of zero.

Enable	Check this box to enable phase offset correction.
Phase Offset	Enter a value to add to all of the phase angle values in the phase image.  Values range from -180 to 180 degrees.
Update	Click this button to calculate and display the phase image.

Noise Reduction

The Phase image is created by calculating the inverse Tangent of the following ratio: (Single Phase Image at -90 degrees) / (Single Phase Image at 0 degrees).  If pixel values in the Single Phase Image at -90 or at 0 degrees are too low, the resulting calculated phase angle will be noisy and unreliable.  Noise reduction "zeroes" noisy pixel values by setting them equal to -360 degrees (the most negative phase angle).

Enable	Check this box to enable phase image noise reduction.
Threshold	Enter the threshold value for the pixel values in the Single Phase Image at 0 and -90 degrees.  Values range from 0.000 mK to 10.000 mK.
Update	Click this button to calculate and display the phase image.
Increment	Select the amount that the Threshold setting is incremented or decremented when using the mouse or arrow keys.
Zero	Click this button to set the Threshold value to 0.

Overlay Merge

A thermal image or picture overlay can be merged with the Lock-in image to facilitate locating the xy coordinates of device heating.  A thermal overlay is a grayscale thermal image of the device and is created by averaging all of the captured images that have been accepted in the LIT test.  When thousands of images have been accepted, the thermal overlay image has very low noise level and provides a high resolution image for locating defects.  The grayscale color palette that is applied to the thermal overlay associates the black end of the palette to the lowest temperature in the thermal overlay image and the white end to the highest temperature.  A picture overlay is created using the Overlay window.  To merge the overlay with the Lock-in image, pixels in the Lock-in image with the highest values replace corresponding pixels in the overlay.  The temperature range of the replacement pixels is determined by the Range level.

Show	Check this box to calculate and display the merged overlay each time the Lock-in image is calculated and displayed.
Contrast	Check this box to enhance the thermal overlay contrast according to the Image Sectors and Histogram Limit settings in the Lock-in Advanced Settings window.
Picture	Check this box to create the merged overlay using the picture from the Overlay window.  Uncheck this box to create the thermal overlay.
Refresh	Click this button to update the thermal overlay after changing the Max or Min.
Scale	Click this button to open the Thermal Overlay Palette window.
Auto Scale	Click this button to automatically scale the thermal overlay.
Max	This setting determines the highest angles in the phase image that replace corresponding pixels in the thermal overlay.  Drag the trackbar handle to change the value. Tip: You can also hover over the trackbar and use the mouse scroll wheel to change the value.
Min	This setting determines the lowest angles in the phase image that replace corresponding pixels in the thermal overlay.  Drag the trackbar handle to change the value. Note: If Noise Reduction is enabled, setting Min to -360 degrees will include all pixels that have been set to -360 degrees in the noise reduction process.

Cursor Info

Temp	This field displays the phase image pixel value at the mouse cursor location.
Location	This field displays the XY coordinates at the mouse cursor location.

Region Tools

You can draw one Region of any shape or size on the phase image in order to view maximum, minimum, and mean values of the pixels enclosed by the region.  When the Auto Scale Region box is checked, the Palette Max and Min values are set to the highest and lowest phase angles within the Region.

To help in locating device heating, the Region can be copied to/from the Main Image or the Lock-in Thermography window.

Select	Select this button to position, resize, and rotate the Region.
Point	Select this button and then click on the image to create a Point Region.
Line	Select this button and then click and drag on the image to create a Line Region.
Rectangle	Select this button and then click and drag on the image to create a Rectangle Region.
Ellipse	Select this button and then click and drag on the image to create an Ellipse Region.
Polyline	Select this button and then click on the image to locate the first vertex of the Polyline Region.  Click to locate each vertex and then right-click on the last vertex to complete the polyline.
Polygon	Select this button and then click on the image to locate the first vertex of the Polygon Region.  Click to locate each vertex and then right-click on the last vertex to complete the polygon.
Delete Region Color	Click this button to delete the Region.

Invert Region Color	The default color of an unselected Region is white.  If the Region is difficult to distinguish from lite background colors, press this button to set the unselected Region color to black.
Scale Legend	Press this button to display a scale legend in the top left corner of the phase image. The size of the legend is determined by the Scale Legend Width setting in the Measure window.
Show Center	Press this button to display a large cross hairs in the center of the phase image.
Measure Distance	Press this button to display the Measure Distance window.

Max, Min, Mean	These fields display temperature statistics within the Region or the entire table if no Region exists.
Image Transfer	Choose to copy the Region to/from the Main Image or the Lock-in Thermography window.
Send	Click this button to copy the Region to the image selected in the Image Transfer option.
Get	Click this button to copy the Region from the image selected in the Image Transfer option. Note: If there are multiple Regions on the Main Image, the first Region is copied.

Setting Up a Test

Description

The Test Setup window (see Figure 5) is used to adjust test parameters when setting up a new Lock-in Thermography (LIT) test.  To open this window, click the Test Setup item under the Setup menu (or click the  button on the top toolbar) of the Lock-in Thermography window.

Figure 5: Test Setup window

Cycle Frequency

Cycle Frequency is the number of power cycles performed per second.  In most test scenarios, a device is powered during the first half of each cycle and unpowered during the second half.  For example, if Cycle Frequency = 1.000 Hz, power is turned on for 0.5 seconds and then turned off for 0.5 seconds. 

The appropriate value for Cycle Frequency typically depends on the configuration and thickness of the device.  A higher Cycle Frequency (1.000 Hz and higher) is used for unencapsulated devices.  Packaged devices require a lower Cycle Frequency.  Very thin packaged devices can possibly be tested with a frequency of 1.000 Hz.  Thicker devices and circuit boards however, may require a Cycle Time of up to 5 seconds (frequency of 0.2 Hz) so that heat generated between board layers or inside components has time to conduct to the surface where it radiates out to the camera.

Cycle Frequency can be increased to improve hot spot spatial resolution by reducing thermal spread but will also decrease the maximum temperature reached during each cycle, reducing test sensitivity.

Cycle Frequency	Select the appropriate test frequency.  Values range from 1 to 15 Hz for the IS640 camera.  The IS640-NLR* camera is limited to 2 Hz due to its lower frame capture rate. Note: Cycle Frequency cannot be changed after a lock-in test has begun.
Cycle Time	For frequencies below 1 Hz, set Cycle Time to the length of one cycle.  Values range from 2 to 60 seconds. Note: Cycle Time cannot be changed after a lock-in test has begun.

*No export license required

Test Duration

Continuous Test	Check this box to continue the LIT test until the OFF button is pressed on the Lock-in Thermography window.
Test Time	Enter the number of hours, minutes, and seconds to run the test.  After the specified time has elapsed, the test will end. Note: At least one lock-in cycle must be completed before the test will stop.  Therefore, if Test Time is less than Cycle Time, the test will continue to run until the first cycle is complete.

Power Mode

On/Off	Select this mode to power on for the first half of the cycle and then power off for the second half of the cycle (50% duty cycle).
Pulse	Pulse mode turns power on for a short duration at the beginning of each cycle. Note: When an instrument is enabled, a measurement will be triggered on the instrument at the end of each pulse and immediately before the next pulse, but only if there is adequate time for the instrument to process each measurement.  If there is not adequate time, measurements are triggered only at the end of the first pulse and immediately before pulse two.
Pulse Length	Enter the lens of each pulse in milliseconds.  Minimum pulse length is 5 ms.
Pulses per Cycle	Enter the number of pulses in each cycle.  Maximum is 8 pulses.
Max Freq	This field displays the maximum test cycle frequency possible given the current values of Pulse Length, Pulses per Cycle, and instrument Protocol.

Test Resolution

Test Resolution determines the smallest temperature change that can be resolved and the range of temperature changes that can be displayed in a Lock-in image. On the other hand, lock-in test sensitivity is determined primarily by how long the test is run and the f/# (or Numerical Aperture for lenses with magnification greater than 1x) of the lens is installed on the camera.

10 µK

This option provides resolution of 10 µK (0.00001°C). Choose this option when testing devices with low levels of power dissipation that heatup below 550 mK (0.55°C). Note: Temperature units of the Lock-in image scale are millikelvin (mK) and the scale range is -100 to 550 mK (-0.10 to 0.55°C). Important: Heating greater than 550 mK will exceed the data format, resulting in 16 bit integer overflow where higher values wrap around to zero and are displayed as low values.

10 mK

This option provide resolution of 10 mK (0.01°C).  Choose this option when testing devices with higher power dissipation that heatup more than 550 mK. Note: Temperature units of the Lock-in image scale are Kelvin (K) and the scale range is -100 to 550 Kelvin (-100 to 550°C).

Image Update

Lock-in images to be calculated and updated at the end of each cycle.  Calculating Lock-in images however, require significant processing resources and may temporarily delay the acceptance of captured thermal images into a test.  To minimum such delays, the frequency at which Lock-in images are updated can be reduced by entering the minimum time period between updates.

Minimum

Enter the time period between updating (calculating and displaying) Lock-in images.  Values range from 1 to 60 seconds.

Auto Save Test

LIT tests can be automatically saved to file at defined intervals while the test continues to run.  This feature preserves test data periodically in case the test is stopped for any reason such as power failure or device damage.

Enable

Check this box to enable automatic test file saving.  LIT tests are saved in a "day" folder, within a "year month" folder, within the "Optotherm\Thermalyze\LIT\AutoSaveTest" folder.

Period

Enter the time period between LIT test saves.  Values range from 1 to 60 minutes. Important: Each automatically saved LIT test file is approximately 150 MB in size.  Therefore, to avoid using up too much hard disk space, set Period to higher values when running long LIT tests.  Furthermore, make sure to delete automatically saved test files that are not needed at the end of each long-running test.

Prolonged Testing

When running a lock-in test over the course of many hours, it is possible to experience an interruption in Camera Communication.  Check the Auto Restart box to automatically reestablish camera communication and then automatically restart the test when such an event occurs.

Auto Restart

Check this box when running a long LIT test of many hours to automatically reestablish camera communication and restart the test if an interruption in camera communication occurs.

Advanced Settings

Description

Settings that control image rejection and noise reduction are found in the Advanced Settings window (see Figure 6).  To open this window, click the Advanced Settings item under the Setup menu (or click the  button) on the Lock-in Thermography window.

Figure 6: Advanced Settings window

Restore Defaults

Click the Restore Defaults item on the Settings menu to restore all setting in the window to their factory default values.  The default settings are appropriate for Lock-in Thermography (LIT) tests with Test Resolution set to 10 microk.

Cycle Initialization

After a period of time, and depending on the applied power and device thermal conductivity, the average temperature of a test device will eventually stabilize.  As the average temperature gradually increases, the phase angle values in the phase image will gradually move to less negative values until the temperature has stabilized.

cycles

Enter the number power cycles to perform before incorporating data into the LIT test.  Initialization cycles allow the device temperature to stabilize before Lock-in and phase images are calculated and displayed.  Values range from 0 to 100 cycles. Note: The effects of cycle initialization on phase angle are negligible unless device heating is significant (greater than 1°C).  Therefore, set this value to zero for low levels of heating and when the phase image is not needed.

Touchup Delay

If your camera includes a physical shutter in front of the detector and the shutter touchup feature has been enabled for your camera, corrupt images can occur immediately following a touchup calibration if the shutter has not opened completely before thermal images are displayed.

sec	Enter the length of time that must elapse after a touchup calibration before images can be accepted into the LIT test.  Values range from 0 to 10 seconds.

Image Rejection

LIT tests are sometimes performed for long periods of time (many hours) to improve sensitivity in order to detect very low levels of heating.  During long tests, there is an increased possibility that corrupt images may be included in the test data.  Corrupt images are usually caused by convection from the environment to the target, from background emittance reflecting off of the target, or from rapid changes in target temperature.  Because the level of device heating during a long test is typically very low, a single corrupt image can overwhelm true test data, preventing faults from being detected.  Therefore, it is essential that each captured image is evaluated so that corrupt images are identified and discarded before they can be incorporated into the test.  Corrupt images are identified by evaluating image statistics of a differential image (Delta Avg image) created by subtracting each captured image from an average of recently captured images (Average Test Image).

Enable	Check this box to enable image rejection. Tip: This box should be unchecked when Test Resolution is set to 10 mK because device heating will prevent significant numbers of captured images to be rejected.
History Weight	The Average Test Image is calculated by averaging new test images with a weighted sum of previously captured images.  Enter the weight factor to apply to the Average Test Image.  Values range from 50 to 99%. Tip: A lower history weight will allow the Average Test Image to adapt to more recent changes in target and room temperature.  A higher weight will prevent rapid temperature changes from being accepted into the test.
Auto Rejection Enable	Check this box to enable automatic adjustment of Rejection Criteria including the Change Max, Change Mean, and Change Std Dev settings.  Automatic settings are determined by calculating image statistics of a differential image (Delta Prev image) created by subtracting each captured image from the previously captured image.
Auto Rejection Safety Factor	New values of Change Max, Change Mean, and Change Std Dev are calculated by multiplying the value of Auto Rejection Safety Factor by image statistics of the Diff Prev image and then adding Auto Rejection Safety Margin.  Increase this setting to raise the value of Rejection Criteria and reduce the number of rejected images.  Values range from 1 to 5x.
Auto Rejection Safety Margin	New values of Change Max, Change Mean, and Change Std Dev are calculated by multiplying the value of Auto Rejection Safety Factor by image statistics of the Diff Prev image and then adding Auto Rejection Safety Margin.  Increase this setting to raise the value of Rejection Criteria and reduce the number of rejected images.  Values range from 0 to 5K.
Change Max	A captured image is determined to be corrupt if the maximum of all pixels in the Delta Avg image exceeds the value of this setting.  Values range from 0 to 10K. Tip: If this value is set too low, a high number of captured images will be rejected.  If this value is set too high, it is more likely that a corrupt image will be incorporated into the test.
Change Mean	A captured image is determined to be corrupt if the mean of all pixels in the Delta Avg image exceeds the value of this setting.  Values range from 0 to 10K. Tip:  If this setting is too low, a high number of captured images will be rejected.  If this value is set too high, it is more likely that a corrupt image will be incorporated into the test.
Change Std Dev	A captured image is determined to be corrupt if the standard deviation of all pixels in the Delta Avg image exceeds the value of this setting.  Values range from 0 to 10K. Tip:  If this value is set too low, a high number of captured images will be rejected.  If this value is set too high, it is more likely that a corrupt image will be incorporated into the test.

Automatic Image Rejection

In most cases, Auto Rejection should be enabled and will automatically adjust Rejection Criteria according to the noise level of captured images.  Auto Rejection settings should only require adjustment if the ambient thermal noise surrounding the test device changes significantly.  Follow these instructions to adjust the Auto Rejection settings.

1. Set the Safety Margin setting to 0K.

2. Reduce the Safety Factor setting until the Change Max box blinks red intermittently and then increase the setting until no red blinking occurs.

3. Increase the Safety Margin setting until no blinking occurs in the Change Mean and Change Std Dev boxes.

4. During a test, if you notice a substantial increase in the number of images in the Rejected field on the Lock-in Thermography window, you may need to readjust these settings.

Manual Image Rejection

If adjusting Rejection Criteria settings manually, appropriate values will depend on factors including Calibration Range, camera lens, and on the ambient thermal noise surrounding the test device.  Follow these instructions to manually adjust the Rejection Criteria.

1. Reduce the Change Max setting until the setting's box blinks red intermittently and then increase the setting until no blinking occurs.

2. Repeat steps 5 and 6 to adjust the settings for Change Mean and Change Std Dev.

3. During a test, if you notice a substantial increase in the number of images in the Rejected field on the Lock-in Thermography window, you may need to readjust these settings.

Noise Reduction

Image noise can conceal low levels of localized heating.  Noise reduction decreases a specific type of random spatial image noise commonly called salt-and-pepper noise using a rank filter.

Enable	Check this box to enable image noise reduction. Tip: Noise reduction should typically be enabled as it significantly reduces salt-and-pepper noise in Lock-in images, allowing much lower levels of heating to be distinguished.
Matrix Size	Choose the matrix to use with the rank filter.  The matrix determines the neighboring pixel used in the noise removal algorithm.  A larger matrix will remove more noise but will decrease image resolution and contrast. Note: The factory default value of Matrix Size is 3x3 cross.

Image Smoothing

Image noise can conceal low levels of localized heating.  Image smoothing is a low-pass filter that decreases Gaussian noise that is generally associated with digitizing analog signals.

Enable	Check this box to enable image smoothing.  Tip: Image smoothing should typically be enabled as it significantly reduces spatial noise in Lock-in images, allowing much lower levels of heating to be distinguished.
Matrix Size	Enter the size of the matrix to use for image smoothing.  The matrix determines the neighboring pixel used in the noise removal algorithm.  A larger matrix will remove more noise but will decrease image resolution and contrast. Note: The factory default value of Matrix Size is 5 x 5.
Strength	Enter the smoothing strength.  Higher values will increase smoothing but will decrease image resolution and contrast.  Values range from 1 to 5. Note: The factory default value of Strength is 2.

Relay/Output Timing

The timing within each cycle when power is applied is critical when calculating phase angles and phase images.  To compensate for communication and activation delays associated with relay devices and other instruments, communication needs to be initiated somewhat earlier than the beginning of the first cycle frame (to apply power) and middle of each cycle (to remove power).  For relay devices, this setting should be set to "previous frame end".  For USB instruments, this setting should be set to "last frame end".

Important: Relay/Output Timing should be changed only if you are instructed to do so by an Optotherm support engineer.

Overlay Contrast Enhancement

Adaptive histogram equalization can be used to enhance the contrast of the thermal overlay image to better visualize features.

Image Sectors	Enter the number of horizontal and vertical image sectors.  The thermal overlay image is divided into sectors and histogram equalization is used to optimize contrast in each sector.
Histogram Limit	Enter the maximum percentage of pixel values that can be assigned to any histogram bin.  Thermal overlay images are 16 bit images, resulting in 65,536 discreet possible values for each pixel.  A value of 1%, for example, limits the number of discreet pixel values to 655 for any histogram bin.

Instrument Control

Description

To open the Instrument Control window (see Figure 7), click the  button on the Sequence toolbar, of select the Instrument Control item from the Setup menu (or click the  button on the top toolbar) of the Thermal Model Comparison window or Lock-in Thermography window.

Figure 7: Instrument Control window

Setup Menu

Settings	Open the Instrument Settings window.
Startup	Open the Instrument Startup window.
Safety	Open the Instrument Safety window.

Instrument Selection

Detect Instruments	Click this button to detect the instruments connected to the computer and list them in the Select Connected Instrument combo box. The instruments that can be detected are Keithley USBTMC (USB test and measurement class) via USB instrument interface and USBTMC via GPIB instrument interface.
Select Connected Instrument	Select a connected instrument to use. Instruments with a USB interface are listed, for example, as "USB0::0x05E6::0x2612::4482980::INSTR" where "USB0" designates the USB interface, "0x05e6" designates the Keithley Instruments vendor ID, "4482980" designates the instrument serial number, and "0x2612 designates the model number, and "INSTR" designates the USBTMC protocol. Instruments with a GPIB interface are listed, for example, as "GPIB0::18::INSTR" where "GPIB0" designates the GPIB interface, "18" designates the GPIB address selected on the instrument, and "INSTR" designates the USBTMC protocol.
Open Connection	Click this button to establish a connection with the selected instrument. Note: A connection to the instrument must be opened before the instrument can be controlled.
Enable Instrument	Check this box enable the instrument for use during Sequence, TMC, and LIT tests. Note: When this box is checked, the instrument output is used in place of Sequence Relays, TMC Relays, and LIT Relays. Important: The Instrument Control window must be open to issue commands to the instrument during Sequence, TMC, and LIT tests.

Instrument Information

Select Model

Select the model that is selected in the Select Connected Instrument combo box.

Command Protocol

Select the instrument communication protocol, SCPI (Standard Commands for Programmable Instruments) or TSP (Test Script Processing).  SCPI is an older generic command set supported by older instruments.  TSP is a Keithley proprietary command set supported by newer Keithley instruments.  Not all Keithley instruments support both protocols. Important: The protocol will also need to be selected on the instrument.  On a 2450 graphical series source measure unit, the communication protocol can be found under System >> Settings >> Command Set.

Source Settings

Sourcing	Choose to source either voltage or current.
Channel	Choose the instrument channel to use.
Setup Instrument	Click this button to setup the instrument with the selected source and measure settings.  When instrument settings are changed, the message "* Setup Required" is displayed to the right of the button until the instrument has been setup with the new settings. Note: The instrument must be setup before a test can be started.

Source Voltage

Voltage High	Enter the output voltage during a Sequence or TMC test, and the first half of each cycle of a lock-in test. Note: The voltage measurement range is determined by the larger absolute value of the Voltage High and Low settings.
Voltage Low	Enter the output voltage during the second half of each cycle of a lock-in test.
Current Limit	Enter the maximum output current. Note: This value may be automatically limited to the Safety Current Limit if the source voltage exceeds the Safety Voltage Limit. Important: When Current Limit is exceeded during a test, instrument output response may slow significantly as output voltage is reduced to lower current below the limit level.  This may result in voltage and current readings that do not reflect values when the output settles.
Current Range	Enter the current measurement range.  When testing circuits with high capacitance or inductance, setting the range higher than Current Limit can help prevent damage to instrument output circuitry.  To set the current measurement range equal to Current Limit, set this value lower than Current Limit. Note: Some instrument models require Current Limit to be within a specific percentage of Current Range and will issue an error if this value is set too high.
Test	Check a box to turn on and test the instrument high or low voltage output.  Uncheck a box to turn off the output.  These boxes are used during test setup to confirm electrical connection and to evaluate power and resistance dissipation in a defect to estimate required testing time.

Source Current

Current	Enter the output current during a Sequence or TMC test, and the first half of each cycle of a lock-in test. Note: The current measurement range is determined by this setting.
Voltage Limit	Enter the maximum voltage output. Note: This value may be automatically limited to the Safety Voltage Limit if the source voltage exceeds the Safety Current Limit. Important: When Voltage Limit is exceeded during a test, instrument output response may slow significantly as output current is reduced to lower voltage below the limit level.  This may result in voltage and current readings that do not reflect values when the output settles.
Voltage Range	Enter the voltage measurement range.  When testing circuits with high capacitance or inductance, setting the range higher than Voltage Limit can help prevent damage to instrument output circuitry.  To set the voltage measurement range equal to Voltage Limit, set this value lower than Voltage Limit. Note: Some instrument models require Voltage Limit to be within a specific percentage of Voltage Range and will issue an error if this value is set too high.
Test	Check a box to turn on and test the instrument current output.  Uncheck a box to turn off the output.  This box is used during test setup to confirm electrical connection and to evaluate power and resistance dissipation in a defect to estimate required testing time.

Measurement Readings

Timed: Enable	Check the Enable box to conduct real-time instrument measurements on the instrument front panel which are then displayed at the bottom of the Instrument Control window.  Timed readings are performed when a voltage or current test box is checked and during Sequence and TMC tests. Important: When controlling an instrument remotely via USB or IEEE-488, continuous measurement triggering enables the instrument to conduct measurements continuously when the Test box is checked (see above).  If this feature is not available on your instrument, then the Timed: Enable box must be checked to conduct measurements while testing the instrument output.  See the Instrument Model Feature Support table to determine if your instrument support continuous measurement triggering.
Reading Rate	Enter the real-time instrument read frequency.
Lock-in Test: Enable	Conduct real-time instrument measurements on the instrument front panel which are then displayed at the bottom of the Instrument Control window.  LIT Test readings are performed during LIT tests after changes in output. Note: Measurements can be read from the instrument during LIT tests only when Cycle Frequency is 1Hz and lower to prevent disrupting cycle test timing.
Read Delay	This setting determines when current and voltage are read from the instrument after a change in output during a lock-in test.  Increase this setting to delay current and voltage measurements, allowing adequate time for the instrument output to settle and to conduct measurements. Note: Changes in output voltage and current and their measurement are very fast but not instantaneous.  Additionally, the magnitude of voltage and current output and settings including High and Low, High Capacitance Mode, Current Limit, NPL Cycles, and Auto Zero determine instrument output settling time and measurement speed.
Take Reading	After checking a voltage or current test box to turn on instrument output, click this button to read and display the output current and voltage until the instrument output has settled.
Send Values	Click this button to send the values in the Current, Voltage, Power, and Resistance fields to the status bar in the Lock-in Thermography window and to the Lock-in Advanced Save and Export window.
IV Curve	Click this button to open the IV Curve window.
Current [mA]	Display field for the measured current in units of milliamps.
Voltage [V]	Display field for the measured voltage in units of volts.
Power [µW]	Display field for the power dissipation in the resistive short circuit of leakage current site in units of microwatts.  Power is calculated by multiplying the measured current and voltage. Tip: Power dissipation in a resistive short is used to estimate the LIT test time required to detect the defect.
Resistance [Ω]	Display field for the resistance of the short circuit of leakage current site in units of ohms.  Resistance is calculated by dividing the measured voltage by the measured current.

Relay Setup

Description

Relay outputs are used to control power to a device during a Lock-in Thermography (LIT) test.  To open the Relay Setup for Lock-in Thermography Tests window (see Figure 8), select the Relay Setup item from the Setup menu (or click the  button on the top toolbar) on the Lock-in Thermography window.

Figure 8: Relay Setup for Lock-in Thermography Tests window

Relay Device Type	Choose the relay device that is connected to your computer.
Initialize Selected Device	Click this button to detect and establish communication with the selected relay device.
Enable Relays	Check this box enable all relays in the selected device. Note: This box must be checked in order for any relays to be activated.
Relay (0 to 7)	There are 8 relays (numbered 0 through 7) that can be used to control power to a device under test.  Each relay can be programmed to activate and deactivate at a specific time while recording an image sequence.  To enable a relay, check its corresponding box.
Activate (0 to 7)	These controls are disabled for LIT tests.  The period of time that a device is powered is determined by the Cycle Time and Power Mode.
Deactivate (0 to 7)	These controls are disabled for LIT tests.  The period of time that a device is powered is determined by the Cycle Time and Power Mode.
All On	Click this button to activate all enabled relays.
All Off	Click this button to deactivate all enabled relays.
Status (click to test)	Check a box to manually activate a relay.  Uncheck the box to deactivate a relay.  Mechanical and reed relays will make a soft click when activated or deactivated.  Solid state relays will be silent.

Thermal Overlay Palette

Description

The Thermal Overlay Palette window (see Figure 9) contains controls to adjust the contrast of the color palette used to display the thermal overlay image on the Lock-in Thermography window and Phase Image window.  To open the Thermal Overlay Palette window, click the Scale button on the on the Lock-in Thermography window or Phase Image window.

Figure 9: Thermal Overlay Palette window

Palette Controls

Auto	Click this button to set the palette max and min values to the highest and lowest temperatures in the thermal overlay image.
In	Click thus button to zoom in to the palette slider scale in order to make fine adjustments.
Out	Click this button to zoom out of the Palette slider scales in order to make course adjustments.
Auto Scale Each	When this box is checked, the palette is automatically scaled when the Lock-in image is updated.
Palette Max and Min Sliders	The color palette can be scaled within a specific temperature range by dragging the palette Max and Min sliders.  Adjust the sliders to improve the contrast of the thermal overlay image. The palette temperature range, displayed to the left of the sliders, displays the temperatures represented by the individual colors of the color palette.

Advanced Save and Export

Description

The Advanced Save and Export window allows users to export many Lock-in images at once, and also to save Lock-in Thermography (LIT) tests and export Lock-in images with important information included in filenames.

To open this window, click the Advanced Save and Export item under the File menu of the Lock-in Thermography window.

Figure 10: Lock-in Advanced Save and Export window

File Type	Choose to save the LIT test or to export one or more Lock-in images.
Images to Export	Select all Lock-in images to be exported.  Settings on the Lock-in Thermography and Phase Image windows are used to create the images.  Also select the file type file to export.  Png files are typically a good choice because they are lossless (no loss in image data) and compressed (small file size). Note: Selecting All Single Phase Angles will result in exporting a separate file for each single phase angle.
Include in Filename	Enter a name and select the Lock-in parameters to include in the filename.  Date format is "YYYY-MM-DD".  Time format is "THHMMSS".  Electrical Properties are loaded into the fields by clicking the Send Values button on the Instrument Control window.  These property fields can also be edited directly and cleared.
Save Test	Click this button to save the currently loaded LIT test.
Export Image(s)	Click this button to export the selected Lock-in images.

Defect Depth Analysis

Description

The Defect Depth Analysis window (see Figure 11) is used to describe the internal structure of a semiconductor device and package in order to calculate defect depth based on phase angle data from testing a device on both the top and bottom sides.  To open this window, click the Defect Depth Analysis item under the Tools menu (or click the  button on the top toolbar) on the Lock-in Thermography window.

Figure 11: Defect Depth Analysis window

File

Open Layer Data	Select the binary layer data file (.olay) to open.  Note: The file name of the most recently opened or saved file is displayed at the bottom of the window.
Save Layer Data	Layer data is saved in binary format with a ".olay" extension. Note: When saving a layer data file, the file name that you provide is appended with ".olay" and saved in the "Optotherm\Thermalyze\Defect Depth" folder unless you specify a different folder.
Export Data	The layer data values can be saved to file in ASCII text format (.txt) or binary format (.imb) for import into a spreadsheet program or your own custom application. In ASCII text format, the name of each layer is saved followed by the layer thickness and thermal conductivity.  A tab character separates the name, thickness, and thermal conductivity values.  A newline character (carriage return/line feed) separates one set of layer data from the next. In binary format, all data is saved sequentially with no separators.  The layer name is saved as a length-prefixed string and the layer thickness and thermal conductivity are saved as four-byte floating-point values in little endian format.
Export Window	The Defect Depth Analysis window can be saved to file in the following formats: bmp, jpg, png, and tif.  The size of the exported image is proportional to the size of the window. Note: Exported Defect Depth Analysis windows are saved in the "Optotherm\Thermalyze\Export" folder unless you specify a different folder.
Print	Print the Defect Depth Analysis window. Note: You must have a printer connected to your computer.
Print with Preview	Select this menu item to open the Print Preview dialog before printing.

Toolbar

Add Layer	Click this button to add a new layer.  If a layer is selected, the new layer is added above the selected layer.  If no layer is selected, the new layer is added below the last layer. Tip: Select a layer by clicking in the # column.
Shift Layer Up	Click this button to shift the currently selected layer up one row.
Shift Layer Down	Click this button to shift the currently selected layer down one row.
Delete Layer	Click this button to delete the currently selected layer.
Delete All Layer	Click this button to delete all layers.

Layer Data

#	Displays the number of each layer.
Name	Enter the name of each layer.
Thickness	Enter the thickness of each layer. Note: Any units for thickness can be used, as long as units remain consistent for all layers.  Note that the calculated defect depth has three-decimal precision, therefore choose units that will not require higher precision.
Thermal Conductivity	Enter the thermal conductivity of each layer. Note: Any units for thermal conductivity can be used, as long as units remain consistent for all layers.  Note that the calculated defect depth has three-decimal precision, therefore choose units that will not require higher precision.

Phase Angles

Top Side	Enter the defect phase angle when measured from the top side of the device. Important: Defect power dissipation has an effect on phase angle value.  Therefore, power dissipated in the defect must remain equal and constant when testing both the top and bottom sides of a device.
Bottom Side	Enter the defect phase angle when measured from the bottom side of the device.

Defect Depth

Number of Steps

Enter the depth resolution used to calculate defect depth.  For example, if 1000 is entered for a device having total thickness of 2mm, the calculated depth resolution will be 2mm / 1000 = 2µm.  Keep in mind, however, that defect depth resolution also depends on phase angle resolution, which in turn depends on factors including defect power dissipation, device surface characteristics, and test time length.

Defect Depth

Click the Calculate Depth button to calculate defect depth and display the resulting value in this field.

Test Setup

Lock-in Thermography Window

Open the Lock-in Thermography window.

Camera Setup

1. Press the Camera Communication button  to start communication between the camera and computer.

2. Press the Capture Images button  to start capturing and displaying thermal images.

3. Select the lowest Calibration Range for the currently installed lens.

Test Setup

1. Open the Test Setup window.

2. Select Cycle Frequency to 1 Hz.

3. Check the Continuous Test box.

4. Set Test Resolution to 10 microK.

5. Set Image Update to 10 seconds.

6. Check the Auto Save Test Enable box and set Period to 60 minutes.

Advanced Settings

1. Open the Advanced Settings window.

2. Click the Restore Defaults item under the Settings menu to restore factory default settings.

Lock-in Thermography Window

1. In the Display panel, choose the Amplitude option and uncheck the Phase box.

2. In the Overlay panel, uncheck the Show box.

Positioning the Device and Focusing

1. Set the Enable Image Averaging button to .

2. Position the device so that the area of interest is in view and then bring the lens into focus.

Relay Setup

1. Make sure that the device power supply is unplugged and unpowered.

2. Connect a device power lead through one of the relays in the relay device.  Devices requiring multiple voltage levels will require using a relay for each level.

3. Open the Relay Setup for Lock-in Thermography Tests window, select the Relay Device Type, check the Enable Relays box, and check the box for each relay that will be used.

Program Settings

Save a Program Settings file so that you can recall all of the settings when you need to perform a similar test in the future.

Testing

Start the Test

1. If you previously saved a Program Settings file with appropriate test settings, open this file.

2. Press the Capture Images button  to begin capturing images.

3. Press the Clear Test button to remove all existing test data from memory.

4. Press the ON/OFF button to start the test.  The number of completed cycles and test running time are displayed.  Avoid moving near the device while the test is running to prevent body emittance from corrupting captured images.

5. When the Lock-in Data progress bar reaches 100%, the Lock-in image will be calculated and displayed.

6. You can press the ON/OFF button to stop the test at any point during the test.  If the Continuous Test box is unchecked, the test will end automatically when Number of Cycles is reached.  When the test ends, all activated relays are deactivated to cutoff power to the device (if using an instrument, the output is turned off and voltage is set to zero).

Adjust Image Rejection

While a lock-in test is running, the Rejected field displays the number of captured images that are rejected due to the Image Rejection Criteria.  If images are rejected more often than 1 or 2 images per minute, then either corrupt images are being rejected or the Rejection Criteria are too low.  Corrupt image are usually caused by convection from the environment to the target, from background emittance reflecting off of the target, or from rapid changes in target temperature.  Before increasing image rejection criteria, make sure that none of these issues are causing images to be rejected.  If it is determined that the Rejection Criteria are too low, increase the Auto Rejection Safety Factor and/or Safety Margin settings until the frequency of image rejection is acceptable.

Display Lock-in Images

1. Adjust the Palette Max and Min values to maximize contrast or press the Auto button to automatically set the Palette Max and Min values to the highest and lowest temperatures in the Lock-in image (or region if the Auto Scale in Region box is checked).  When adjusting the values manually, you may only need to adjust the Palette Max value (Palette Min can usually remain equal to zero).  Check the Auto Scale Each box to auto scale the palette each time the Lock-in image is updated.

2. Click the Amplitude button to display the amplitude image showing all temperature increases on the device at any time during the cycle.

3. Adjust the Single Phase Image Phase Angle and then click the Show button (or click the < > buttons) to display the single phase image to identify areas that heat up at different times during the cycle and at different device depths.  Single phase images typically produce the best spatial resolution when locating faults.

4. Adjust the Cycle Sequence Image # and then click the Show button (or click the < > buttons) to display individual cycle images showing lateral heat flow across the device during the power up and cool down intervals of the cycle.

5. To improve the spatial resolution of faults, increase the Cycle Frequency and repeat the LIT test.  Higher test frequencies reduce thermal diffusion into adjacent areas of the device.

Display the Thermal Overlay

1. Check the Show box to merge the thermal overlay with the Lock-in image.

2. Adjust the thermal overlay Range setting to set the range of high-temperature pixels in the Lock-in image that replace corresponding pixels in the thermal overlay.

3. To improve the contrast of the thermal overlay, draw a Region on the Lock-in image enclosing the device and check the thermal overlay In Region box.

Measuring Fault Phase Angle

1. Click the Phase button to display the Phase Image window.

2. Click the Auto button to maximize phase image contrast.

3. Draw a small Rectangle Region enclosing the center of the fault on the phase image.  The phase angle statistics are listed in the Region Tools panel.

Calculate Fault Depth

See the instructions for Calculating Fault Depth.

Test Optimization

Test Sensitivity (Maximizing)

The sensitivity of a Lock-in Thermography (LIT) test is determined by the following factors.

• Test Length

• Lens Sensitivity

• Cycle Frequency

• Noise Level

Test Length

Test sensitivity is inversely proportional to the square root of the number of images captured during a lock-in test.  Therefore, a lock-in test lasting 4 minutes is approximately 2x more sensitive than a 1 minute test.  Due to the "square root" factor, there is a diminishing return of sensitivity as test length increases.  For example, to improve test sensitivity of a 1 hour test by a factor of 2, a test lasting 4 hours is required.  Due to typical environmental sources of thermal noise, the practical limit of test sensitivity is approximately 0.0002 Celsuis (0.2 mK).  Therefore, once the noise in Lock-in images decrease below 0.2mK, there will be minimal improvement in sensitivity if the test is continued.  Usually, this level of sensitivity requires testing for several hours.

Lens Sensitivity

There are four lenses designed for use with the IS640 camera: the Macroscopic, 80 micron, 20 micron, and 5 micron.  The Macroscopic, 80 micron, and 20 micron lenses have approximately the same measurement sensitivity.  The sensitivity of the 5 micron lens however, is approximately six times lower than the other three lenses due to its increased magnification.  When performing initial tests on small devices with low levels of leakage (<500 microwatts), start with the 20 micron lens for optimal sensitivity and spatial resolution.  The Macroscopic or 80 micron lens can be used for larger devices.  After the defect site has been localized, testing with the 5 micron lens can be attempted to improve spatial resolution.

Cycle Frequency

Test sensitivity also depends on Cycle Frequency.  Maximum test sensitivity is achieved when the heating reaches a steady-state level during each cycle.  For this reason, the Cycle Frequency resulting in the highest sensitivity will depend on the characteristics of the device under test.  When testing a bare semiconductor device, for example, highest sensitivity is typically reached at a Cycle Frequency of 1Hz.  For a chip with a plastic package however, maximum sensitivity may be reached at Cycle Time of 4 seconds or longer because a longer period of time must elapse for heat to flow through the package to the surface where it can be detected.

Cycle Frequency can be increased to improve hot spot spatial resolution by reducing thermal spread and to more effectively cancel sources of thermal noise due to the increase in number of cycles.  Increasing Cycle Frequency however, will result in a lower maximum temperature reached, reducing test sensitivity.  In most cases, begin testing a device by setting Cycle Frequency for maximum sensitivity.  Then, after isolating the location of the defect, increase Cycle Frequency to improve spatial resolution.

Noise Level

Because LIT tests involve detecting very small heating (<0.001 Celsius), source of low levels of thermal noise may easily corrupt a test.  For this reason, it is very important to eliminate or minimize noise source near the device under test such as the following.

• Movement of infrared emittance sources such as people or equipment

• Sources of air currents such ventilation drafts (turn off the Thermal stage during LIT tests as the fan will lower test sensitivity)

• Overhead sources of infrared emittance such as heating/AC ducts

Power Dissipation (Level Required)

In order to determine whether a specific leakage current defect can be detected, it is necessary to measure or calculate the power dissipation in the fault.  When testing bare semiconductor devices, current leakage dissipating 100 microwatts can usually be detected in about 1-2 minutes.  Detecting <10 microwatts may require 1 hour or longer.  When testing thick packaged devices, higher power dissipation will be required as heat spread will reduce the maximum temperature detected on the surface of the package.  Packaged devices may require dissipating 500 microwatts (or more) in a fault in order for it to be detected and located.

Lock-in Images (Which to Use)

Single phase images provide the highest sensitivity of all Lock-in images, although they display heating that occurs at one specific time during the cycle.  Amplitude images are somewhat less sensitive, but they display heating that occurs at any time during the cycle.  Single phase images should typically be used for detection of low levels of leakage current.  It is necessary however, to set Phase Angle to the proper value to display defect heating.  Start with Phase Angle set to 0 degrees and decrease until fault heating is discernible.  This image will display fault heating that occurs earliest in the cycle and will provide the best spatial resolution regarding fault location.  Phase Images are primarily used for determining defect depth in devices such as stacked die.

Cycle Sequence (What's it for)

Cycle sequence images are typically not used for leakage current detection and location, but for creating a low-noise sequence of images showing the heating that takes place during one complete cycle.  Cycle sequence images can be helpful when analyzing heat flow during product development.

Rejection Criteria (How to Set)

While a lock-in test is running, the Rejected field displays the number of captured images that are rejected due to the Image Rejection Criteria.  If images are rejected more often than 1 or 2 images per minute, then either corrupt images are being rejected or the Rejection Criteria are too low.  Corrupt images are usually caused by convection from the environment to the target, from background emittance reflecting off of the target, or from rapid changes in target temperature.  Before increasing image rejection criteria, make sure that none of these issues are causing images to be rejected.  If it is determined that the Rejection Criteria are too low, increase the Auto Rejection Safety Factor and/or Safety Margin settings until the frequency of image rejection is acceptable.

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