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

Abstract

Electrolytic and electroless Ni/Au are common pad surface finishes on area array (BGA or CSP) packages and printed wiring boards (PWB). The electroless nickel/immersion gold (ENIG) process often is implemented when there is insufficient space to allow bussing for the more common electrolytic Ni/Au plating. The ENIG process continues to be used despite evidence that it may cause or contribute to catastrophic, brittle, interfacial solder joint fractures. In this investigation a plastic ball grid array (PBGA) test vehicle is used to compare quality and reliability of four variations of the ENIG surface finish. The standard electrolytic Ni/Au surface finish is used as the control cell for the experiment. Ball shear tests and optical and scanning electron microscopy are performed on as-received and thermally preconditioned packages to evaluate package quality prior to assembly. Accelerated temperature cycling (0/+100 °C and -40/+125 °C) is used to evaluate solder joint attachment reliability. Detailed failure mode analysis is used to compare the fracture modes in the ball shear and thermal cycled samples in the electroless and electrolytic packages. The results are discussed in terms of the failure modes and the characteristics of the different Ni/Au surface finishes.

Isothermal aging effects on the microstructure and solder bump shear strength of eutectic Sn37Pb and Sn3.5Ag solders

“…Cracks tend to propagate along the IMCs/solder interface because of the harder and brittle nature of the IMCs. Moreover stress is easily concentrated around the IMCs and therefore solder/IMCs interface failure mode was observed [7,21,24]. Fig.…”

“…When the UBM is thick, a thick top Au layer promotes the IMC formation and therefore tends to result in the IMCs/solder failure mode [7,24,27].…”

“…In the literature, usually cohesive solder failure or solder/IMCs interface brittle failure modes were reported [7,[21][22][23][24]. Thick and flat IMCs have deleterious effects on reliability.…”

“…Solder bump shear strength testing is a fast, cheap and easy controllable method for the solder bump quality control [5]. It provides important solder bump integrity and robustness information, and is the most useful and widely adopted measurement technique for solder bump quality and reliability assessments [5][6][7][8][9]. 0026 Due to the toxic nature of Pb, it will be banned from the European electronic industry in July 2006.…”