Drop test reliability improvement of lead-free fine pitch BGA using different solder ball composition

We present drop test results based on the JEDEC method JESD22-B111 for a laminate based lead-free fine pitch ball grid array (FBGA). We especially focus on the influence of substrate technology and solder ball composition. For all our tests we determine the electrical drop test failure rates until end-of-life and the main failure modes by means of cross sectioning. We compare the results for Sn4AgO.5Cu solder joints, which typically show intermetallic layer cracking along the package pad, with Sn36Pb2Ag solder joints on electroplated NiAu substrates, which typically fail in ductile mode. We find excellent drop test results on Cu-OSP and NiAu substrate finishes using the solder ball composition Sn1.2Ag0.5Cu0.05Ni. With this alloy no intermetallic cracks occurred. The Sn1.2Ag0.5Cu0.05Ni creates different intermetallic composition and is able to absorb more shock stress in its bulk material compared to Sn4AgO.5Cu. This advantageous behavior is confirmed by a dedicated drop test monitoring experiment and by temperature cycling tests using reference alloys.