Wetting behaviors and interfacial reactions of lead-containing and lead-free solder alloys on gold, palladium, nickel foils, leadframes, and under-bump thin film metallizations in electronic packaging.

摘要

We have studied systematically the wetting behaviors (wetting angle and morphology) and interfacial reactions (kinetics) of Pb-containing (eutectic 63Sn-37Pb, 95Pb-5Sn) and Pb-free solders (pure Sn, 96Sn-4Ag, 57Bi-43Sn, 77.2Sn-20In-2.8Ag) on Au, Pd, Ni, and Cu foils using the Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Analysis (EDX). We have also studied the wetting of eutectic SnPb on thin film Ni/Ti/Si, Pd/Ni/Cu, Au/Pd/Ni/Cu, both Sn stripped and eutectic SnPb stripped Pd/Ni/Cu leadframes, and various under-bump metallizations (UBM) such as Au/electroless Ni(P)/Al and electrolytic Ni/Cu-Cr/Cr/Al which might be used for low cost flip chip technology (LCFCT).; In addition, we have characterized the structure of Pd-Sn compound using glancing incidence X-ray diffraction, and have studied the interfacial microstructure of Au/electroless Ni/Al UBM using the transmission electron microscopy (TEM).; The kinetics of Pd-Sn compound growth was studied and the consumption rate of Pd for eutectic SnPb (63Sn-37Pb)/Pd was measured using the mass conservation law. For the Pd/Ni, we used two thicknesses of Pd (760 A and 2500 A) to study the thickness effect. For the Au/Pd/Ni, we used either immersion Au (50 A) or acid Au (50 A) flashed on 1000 A Pd to study the effects of adding Au to the Pd surface. We also investigated the wetting of eutectic SnPb on a PdSn{dollar}sb3{dollar} compound surface. In all these samples, we found the wetting behavior to be time and temperature dependent.; We found a unique feature of a sunken interface for eutectic SnPb and 95Pb-5Sn solders on Au foils mainly due to the high solubility of Au in these solders, but a relatively flat interface formed on Pd foils due to the low solubility of Pd.; Lastly, concerning the interfacial reactions and kinetics of eutectic SnPb on various Ni-based UBM, we found that the lateral penetration of solder occurred along the interface between electroless Ni(P) and silicon oxynitride (Si-O-N) and the penetration is accompanied by Ni-Sn compound formation, which is called reactive interface diffusion. For eutectic SnPb on thin films of Ni/Ti/Si, we have found that the spalling rate of Ni-Sn compound is much lower than that of Cu-Sn compound on Cu/Ti/Si after the consumption of the entire Ni layer.