Thermal performance of laminate-to-aluminum attachment materials

A non-destructive method was used to determine the effects of thermal cycling on the thermal performance of a PCB attached to an aluminum substrate with a thermal adhesive. This method allows for a comparison of the thermal performance of various TIMs in an industrial application. Testing was done on FR4 and Flex hoards, both with and without overmolding, attached using PSA and an alternative adhesive. Baseline measurements were taken, then the boards were cycled from -40 to 125°C on a 90-minute cycle with 15-minute dwells at the target temperatures. It was found that both adhesives showed an increase in thermal conductivity, possibly due to curing, and delamination occurred at 17 out of 35 locations with the alternative adhesive within the first 1000 cycles while no delamination occurred with the PSA.