All thermal designs relying on heat sinks and thermal interface materials (TIM) assume uniform and well bonded interfaces for calculating the heat transfer capability of the structure. The reality is that production processes are not perfect and materials used can change from batch to batch. So how can you confirm the integrity of the thermal interfaces depended on in your design?
One way of evaluating the thermal integrity is by using high frequency ultrasound, commonly known as Acoustic Microscopy (AM), to image and measure the materials continuity at interfaces. AM imaging is very sensitive to air gaps or vacuum voids and thin delaminations down to 0.1 microns, so it can easily determine the flaws that hinder heat transfer through a structure. In addition, it is also possible to measure the thickness uniformity of a TIM or solder material used, which also affects heat transfer.
Case studies will be presented for typical electronics applications, such as multilayer IBGT modules, IC devices with integrated heat sinks and the actual contact area between TIM and heat sinks. The presentation will show the types of issues observed with AM imaging that prevent proper heat transfer through a structure which can also be applied to other applications, such as solar concentrators, power devices, LEDs, etc.