Mechanical Shock Test Performance of SAC105 (Sn-l.0Ag-0.5Cu) and Sn-3.5Ag, BGA Components with SAC305 Solder Paste on NiAu and OSP Board Surface Finishes

摘要

Many BGA and CSP component suppliers have begun shipment of components with a variety of second generation lead-free solder ball alloys based on the improved mechanical shock resistance. Although in general mechanical performance has been improved, there have been questions raised on how much the mechanical performance of these lead-free solder ball alloys can vary with different board surface finishes such as NiAu and OSP. Mechanical testing was performed on Sn3.5Ag and SnlAg0.5Cu 676 PBGA components with lmm pitch and electrolytic Ni/Au finished component pads. These components were soldered with Sn3Ag0.5Cu paste on either electrolytic Ni/Au or high temperature rated OSP board surface finish. The mechanical shock data indicated that among the four board surface finish/BGA component sphere alloy combinations, the SnlAg0.5Cu (SAC105) BGA sphere with NiAu board surface finish had the lowest drop test resistance among the combinations evaluated, which was not expected. Failure analysis of this and the other drop test combinations was carried out by dye-pry analysis and cross-sectioning to understand the failure locations on the soldered BGA joints. The results were assessed in terms of Weibull failure distributions, failure modes, failure locations, and microstructural analysis which included IMC thickness measurement and IMC compositional analysis and distribution. This analysis suggested a possible direct or indirect relationship between drop test results and unique IMC spalling of the Snl Ag0.5Cu (SAC105) BGA sphere with NiAu board finish. The implications of these findings and areas for further study are discussed.