Lock-in Thermography Software Module

How it Works

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 an 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 increase 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.

Applications

• Lock-in thermography tests are used to detect and locate the following faults:
  Thermography
• Leakage current and resistive short circuits on semiconductor devices, wafers, SMD components, bare circuit boards and flex circuits 
• Power-to-ground short circuits on populated circuit boards 
• Photon Emission Testing