Surface Finish of Electroplating Copper/Lead-free Solder on IC substrate
Higher performance substrate is going to be the bigger package size, high layer stack up, multi-chip and thinner thickness package. Those are huge technical challenger especially bump pitch shrinking cased the printing solder on bump pad of substrate will be facing yield drop. Many reliability issues have occurred in various products and need to be studied. Surface finish on substrates in packaging is one of the important topics for discussion. Both electroplating and stencil printing are common methods for surface finish, but electroplating is a better solution for fine bump pitch requirement. In this paper, we used electroplating process to deposit different lead-free solders (Sn, SnAg, SnCu) on C4 bump and BGA pad of substrate for surface finish. The surface finishes were then mounted with Sn-3Ag-0.5Cu solder ball for different reflow condition. The samples were then subjected to ball pull and ball shear test to study the strength of the joints and the fracture mode after multi-reflows and HTST (High Temperature Storage Test). For Sn, SnAg, and SnCu as surface finishes, the results of ball pull and ball shear strength tests are close to 6.2 and 3.5g/mil2 respective. From the observation of fracture mode, SnCu showed a higher ratio for fracture within IMCs in both ball pull and ball shear tests For multi-reflows tests on all three solders, with more times of reflow, the pull strength decreased but the variation in shear strength was not obvious. Furthermore, the fracture mode indicated that the ratio of fracture in IMCs increased with the times of reflow. The grain size and morphology of IMCs are quite different between the tests of multi-reflows and HTST conditions. The overall experimental results indicated that electroplated lead-free solders for surface finish are good candidates for fine bump pitch on IC substrates.
Weihung Lin Wenhung Hu YingChih Chan Hungsheng Hu Shih-Ping Hsu
Phoenix Precision technology Corp
国际会议
上海
英文
2008-03-17（万方平台首次上网日期，不代表论文的发表时间）