Abstract: Controlled amount of heat is injected into a stacked die using a light beam, and the propagated heat is measuring with LIT camera from the other side of the die. The thermal image obtained can be characterized so that it can be used to calibrate the phase shift from a given stack layer, or can be used to identify defects in the stacked die. The process can be repeated for each die in the stack to generate a reference for future testing. The thermal image can be investigated to detect faults, such as voids in vias, e.g., TSV.

Abstract: A non-destructive approach for the 3D localization of buried hot spots in electronic device architectures by use of Lock-in Thermography (LIT). The 3D analysis is based on the principles of thermal wave propagation through different material layers and the resulting phase shift/thermal time delay. With more complex multi level stacked die architectures it is necessary to acquire multiple LIT results at different excitation frequencies for precise hot spot depth localization. Additionally, the use of multiple time-resolved thermal waveforms, measured in a minimized field of view on top of the hot spot location, can be used to speed up the data acquisition. The shape of the resulting waveforms can be analyzed to further increase the detection accuracy and confidence level.