Lock-In Thermography

Description of lock-in thermography analysis

Detecting of failed power electronic devices such as IGBT, MosFETs, diodes, and resistors
Analysis of short circuits, ESD defects, oxide damages, edge termination defects, avalanche brake down, whiskers, and electrical conductive contamination
High sensitivity for hot spot detection with a heat dissipation in the μW range
2D / 3D defect localization for further destructive analysis to identify the failure mechanism

Measurement voltage from mV up to 10kV
Decapsulation of mold compounds as well as silicone gels
Chemical removal of chip topside metallization and contacts for instance bond wires and ribbons out of different materials
Follow up investigations such as cross sections, scanning electron microscopy, micro sections with focused ion beam
Interpretation of test results and failure mechanisms
Consultancy on the different investigated failure modes for instance chip damage due to improper bond wire process parameters

The device under test is pulsed with the rectangular voltage by arbitrary Lock-In frequency (typical: 1 to 25Hz)
Electrical defect dissipate thermal power
Thermal power heats up the surface
Measurement of IR signal infrared camera
Acquisition of amplitude image as well as resulting time dependent step response (phase image)

Differential measurement principle
Best suited for different emission coefficients of the device surface materials
No influence of the ambient (temperature, reflections)
Three different zoom lenses to investigate structures from complete power module to single IGBT cells

After fabrication, a power module failed the final electrical quality test (e.g. gate-emitter leakage current)
Lock-in thermography helps to detect which semiconductor is responsible for the leakage current and determines the exact position of the defect on the device
Next step consists of removing bond wires of the semi conductor followed by a second lock-in thermography analysis to get the micro scale location of the defect
Last step can be a focused ion beam investigation with scanning electron microscopy to detect the cause of failure (e.g. damaged gate structure)