Alternative lead-free solder joint integrity under room temperature mechanical load

This work explored the feasibility of using alternative lead-free solder alloy with lower melting temperatures as board-level interconnects and attempted to establish preliminary baseline reliability under mechanical loads. Solder ball pull and shear tests were first performed at package level. Bend tests were performed at board level with PCB/BGA test coupons under monotonic three-point bending load. In addition to the traditional Sn-Pb solder and current lead-free Sn-Ag-Cu solder, four other lead-free solders (Sn-In, Sn-Bi, Sn-Bi-Ag and Sn-Zn-Al) were tested. For the board level test, surface finishes were immersion silver (ImAg) and organic solderability preservatives (OSP) with package level surface finish of electrolytic Ni and electrolytic Au. The test coupon with surface mounted BGAs has both via-in-pad (VIP) pads and non-VIP pads. The pull, shear and bend test results showed that Sn-In solder has the lowest performance, while Sn-Bi and Sn-Bi-Ag solder compositions showed comparable performance to Sn-Ag-Cu. The work showed that Sn-Zn-Al solder could be a potential choice for lead-free solder alternative. Bend test showed that most of the BGAs with non-VIP pads performed better than those with VIP pads.