Reliability analysis of SnPb and SnAgCu solder joints in FC-BGA packages with thermal enabling preload

Modem semiconductor devices in many applications require a thermal solution to remove the heat away from the device and maintain a certain operating temperature. These thermal solutions typically use a heat sink and a thermal interface material (e.g. thermal grease) between the device and the heat sink. A compressive load is applied to reduce the thermal resistance of the interface and facilitate better heat transfer from the device to heat sink. Depending on the magnitude, this compressive preload may affect the fatigue behavior of second level solder joints connecting the device to PCB in a thermal cycling environment. This paper describes, the experimental setup and test results to evaluate the reliability of solder joints in the presence of a preload. 3-D nonlinear finite element analysis is performed to simulate the effect of compressive load in thermal cycling. Both SnPb and SnAgCu solder alloys are studied with various levels of preload.