Experimental Study of Solder Joint Reliability for External Heat Sink Installation on FCBGA

As the increasing power consumption for electronic devices, thermal management on board level becomes a challenge to manufacturers who are integrating more functionality and components into a board in order to the high performance products in this competitive market. To drive such high level products requires more power consumption and consequently arises a thermal risk of system malfunction because of overheating to chips. A common implement for thermal solution is a heat sink installed on package via clip mechanism that maintained a compressive force to clamp the heat sink and board to fulfill this thermal dissipation demand. But this compressive force along with operation temperature will arise solder joint risk and potentially induce the function failed due to the clamped force may potentially arise solder ball creep after long operating time and damage the connection failed of solder ball and PCB. This paper describes the experimental setup and test results to evaluate the solder joints creep behavior in the presence of clamped force and operation temperature. An External Heat Spreader Flip Chip BGA (EHS-FCBGA) was tested for several weeks under 85°C with a compressive force. The different levels of uniform compressive forces were applied with 25kg and 50kg metal blocks on EHS-FCBGA to simulate the clamped force. All test vehicles were placed in an oven at 85°C for several weeks to accelerate thermal aging condition and measured solder ball collapsed shapes and do open-short test at the end of every two weeks.