Performance and reliability of TIM in high power HFCBGA

HFCBGA is a thermally enhanced FCBGA through mounting a metal heat spreader to the rear side of the chip via thermal interface materials (TIM), where a high thermal conductive silver filler silicone-based TIM is selected. Thermal resistance of junction to case (θJC) is the critical thermal performance index, it's checked not only at the beginning of the product life, but also after several types of reliability tests, include TCT, HTS and HAST. TIM void, BLT and θJC is checked in this experiment. The result shows there has 0~1.3% area ratio TIM void at the center after TCT 500 cycles and keeps at the same level after TCT 1000 cycles; HTS 1000 hours and HAST 96 hours doesn't induce TIM void. However, thermal performance result shows the effect of this tiny void is indistinct. On the other hand, the result shows TIM thickness is correlated to thermal performance. Meanwhile, that the TIM thickness after TCT 1000 is thinner than it before TCT explains why the thermal performance is not only without degradation but even improved after reliability test.