The effect of variations in nickel/gold surface finish on theassembly quality and attachment reliability of a plastic ball grid array

摘要

Electrolytic and electroless Ni/Au are common pad surface finisheson area array (BGA or CSP) packages and printed wiring boards (PWB). Theelectroless nickel/immersion gold (ENIG) process often is implementedwhen there is insufficient space to allow bussing for the more commonelectrolytic Ni/Au plating. The ENIG process continues to be useddespite evidence that it may cause or contribute to catastrophic,brittle, interfacial solder joint fractures. In this investigation aplastic ball grid array (PBGA) test vehicle is used to compare qualityand reliability of four variations of the ENIG surface finish. Thestandard electrolytic Ni/Au surface finish is used as the control cellfor the experiment. Ball shear tests and optical and scanning electronmicroscopy are performed on as-received and thermally preconditionedpackages to evaluate package quality prior to assembly. Acceleratedtemperature cycling (0/+100° C and -40/+125° C) is used toevaluate solder joint attachment reliability. Detailed failure modeanalysis is used to compare the fracture modes in the ball shear andthermal cycled samples in the electroless and electrolytic packages. Theresults are discussed in terms of the failure modes and thecharacteristics of the different Ni/Au surface finishes