FCPBGA with SOP Pad Finishing A Study of Lead-Free Solder Ball Attach Improvement

A comparison study between Sn3.5Ag solder ball and conventional Sn3.8AgO.7Cu (SAC387) solder ball was conducted on 33×33 FCPBGA with SOP pad finishing. After assembly, samples were subjected to laser scanning for slanted ball inspection. Visual inspection under low power scope was done to check for wrinkled balls. Cold ball pull (CBP) was used to evaluate the solder joint strength at 4 conditions, namely after assembly (TO), after six time reflow, after 168 hours high temperature storage (HTS) and after Moisture Sensitivity Level 3/260°C test (MSL3). Cross sectioning was also performed to all condition for intermetallic compound (IMC) measurement and microstructure study. In addition, tray drop test and packing drop test were conducted to assess solder joint integrity due to handling and impact force. Solderability test was also performed to assess any possible failures during board mounting process at customers site. Finally, Sn3.5Ag is recommended to replace Sn3.8AgO.7Cu ball for 33×33mm FCPBGA package with SOP pad finishing to resolve the wrinkled ball which is a customer concern, and to prevent slanted ball yield loss in production, as well as enhancing the overall solder joint performance with higher pull strength.