Defining Mechanical Load Limits for Thermal Solutions on High Performance FCBGA Packages
Authors: Brian Roggeman, Jiantao Zheng, Mark Schwarz, and Ahmer Syed Company: Qualcomm Technologies, Inc. Date Published: 9/27/2015
Abstract: This study aims to determine maximum allowable compressive loads at which the mechanical integrity and reliability of flip chip BGA (FCBGA) packages are maintained. Custom fixtures were fabricated to apply well controlled compressive loads to lidded FCBGA devices. Multiple loads were calibrated to the compression percentage, or bond line thickness, of a particular gap pad TIM material. The risk of heat-sink application was addressed by examining the devices for die cracking and other mechanical damage. Longer term risks were assessed by subjecting devices under compression to high temperature aging, which simulates and accelerates an enduse condition. Daisy chains encompassing both the BGA solder balls and die interconnects were monitored in-situ for opens and shorts. Samples were also selectively removed from aging to measure BGA collapse in highly loaded areas and to determine the risk of solder bridging. In addition, the effect of compressive loading on reliability was examined in temperature cycle testing from -40 C to 125 C. Finally FEA modeling was developed to generalize the test results and aid in the development of maximum loading recommendations for any package type. A summary of the data and recommendation for maximum allowable loading, based on mechanical behavior is documented.