Interfacial reaction of Sn-3.5wt%Ag solder alloy with a variance of Ni layer thickness

Abstract

Sn-3.5Ag (compositions are all in weight percent unless specified otherwise) solder alloys were soldered on the various substrates of bare Cu plate, Cu plate/Ni(2㎛), Cu plate/Ni(4㎛), and bare Ni plate. The morphology, composition and phase identification of the intermetallic compounds(IMC) at the interface were examined using Scanning Electron Microscopy(SEM) and X-ray diffraction(XRD). With varying the Ni layer thickness, various IMCs were formed, which were Cu_6Sn_5 on bare Cu plate, metastable NiSn₃ ＋ Ni₃Sn₄ on Cu plate/Ni(2㎛), Ni₃Sn₄ on Cu plate/Ni(4㎛) and Ni₃Sn ＋ Ni₃Sn₄ on bare Ni plate. And it was also observed that the wetting behavior was dependent on the Ni layer thickness. Such phenomena seemed to be caused by the type of IMCs differently formed on each substrate. As the soldering time was increased, the changes of the IMC morphology and the wetting behavior were observed on the various substrates. Therefore it was postulated that the Ni layer thickness should be considered as an important parameter in the interfacial reaction and the wetting behavior.