Factors affecting the Dynamic Bending Reliability of Pb-free Solder Joints in Board Level BGA and Bare Si-Die Flip Chip Packages

초록

From the past few years, Sn-3.0(wt.%)Ag-0.5Cu has been used as a representative Pb-free solder alloy in the electronic industry. However, SAC305 solder joint was reported to be suffered from brittle behavior on the mechanical shock condition. This brittle nature of SAC305 joint is believed to be improved by increasing the ductility of solder material. Moreover, this is expected to be important in bare silicon die flip chip package in which the crack tends to occur in silicon side. In this study, the effects of solder and solder joint properties on the dynamic bending reliability of both board level BGA and bare silicon die flip chip packages were studied. Solder balls of Sn-1.2Ag-0.7Cu-0.4In, Sn-1.2Ag-0.7Cu-0.4In-0.1Mn, Sn-1.2Ag-0.7Cu-0.4In-0.1Pd, SAC305, SAC105 compositions were prepared to be 450㎛ in diameter. BGA chip supplied by TopLine and bare silicon die made by ourselves were surface mounted on FR-4 PCB having thickness of 1mm. During the dynamic bending reliability test, the strain of PCB was step increased from 0.2% to 1.5% until the failure circuit was detected with 50㎑ sampling rate. It was found out that role of solder joint seemed to be different in board level BGA and bare silicon die packages.