An accelerated reliability test method to predict thermal grease pump-out in flip-chip applications

In packages using thermal grease as the conducting medium between the die and the thermal solution, grease pump-out during operation of the part is a known failure mechanism. Traditional power cycle test is a direct method to examine grease reliability. However, it is a time consuming process due to its long heating and cooling times. In order to screen numerous thermal grease materials during the initial design phase of a microprocessor package, it is advantageous to utilize a quick turn test. This paper describes an accelerated mechanical test, developed to evaluate interface degradation, due to pump-out. An MTS(R) universal testing machine is used to simulate the squeezing action on the grease, caused by die warpage change. By using this accelerated testing method, product design cycle time can be significantly reduced. In this paper, a silicone-oil-based AlN-filled thermal grease with different thickness at the corresponding device operation temperature is examined by using this accelerated test method. Results from this test are also compared to traditional power cycle test results.