Accelerated Stress Testing and Failure Analysis of Thermal Greases

Thermal greases allow a low stress bond at low bond line thicknesses (BLT) at medium thermal conductivities and simple application, all of which make it an alternative to solders, thermal adhesives or pads as thermal interface material (TIM) for power and microprocessor applications. However, for several years now thermal overload failure has been a pressing problem due to pump-out of thermal grease as die or module-level thermal interface material, but no in-depth understanding of the involved failure mechanisms or an accelerated test for grease qualification is still missing. These points are addressed in this paper: We show a couple of accelerated test setups to achieve substantial acceleration, being as close to the thermomechanical drive of the original package architecture. Finally, the lessons learned are bundled within a new test rig, called the GPOT (Grease Pump-Out Tester) which allows plug and play operation for high throughput testing of thermal greases. Scientific insight is gained from in-situ observation of grease degradation, allowing an identification of failure mechanisms, influential material and stress test parameters as well as first simulations and guidelines for grease selection and reliability.

Automated summary

Thermal greases are an alternative to solders, thermal adhesives or pads as thermal interface material (TIM) for power and microprocessor applications. The problem of thermal overload failure due to pump-out of thermal grease has been addressed in this paper. Accelerated test setups and a new test rig called the GPOT have been introduced to gain scientific insight into grease degradation and provide guidelines for grease selection and reliability.