The formation of intermetallic layer structure of SAC405/Cu and SAC405/ENImAg solder joint interfaces

Abstract

Purpose

The surface finish is an essential step in printed circuit boards design because it provides a solderable surface for electronic components. The purpose of this study to investigate the effects of different surface finishes during the soldering and ageing process.

Design/methodology/approach

The solder joints of Sn-4.0Ag-0.5Cu/Cu and Sn-4.0Ag-0.5Cu/electroless nickel/immersion silver (ENImAg) were investigated in terms of intermetallic (IMC) thickness, morphology and shear strength. The microstructure and compositions of solder joints are observed, and analyzed by using scanning electron microscopy (SEM-EDX) and optical microscope (OM).

Findings

Compounds of Cu₆Sn₅ and (Cu, Ni)₆Sn₅ IMC were formed in SAC405/Cu and SAC405/ENImAg, respectively, as-reflowed. When the sample was exposed to ageing, new layers of Cu₃Sn and (Ni, Cu)₃Sn₅ were observed at the interface. Analogous growth in the thickness of the IMC layer and increased grains size commensurate with ageing time. The results equally revealed an increase in shear strength of SAC405/ENImAg because of the thin layer of IMC and surface finish used compared to SAC405/Cu. Hence, a ductile fracture was observed at the bulk solder. Overall, the ENImAg surface finish showed excellent performance of solder joints than that of bare Cu.

Originality/value

The novel surface finish (ENImAg) has been developed and optimized. This alternative lead-free surface finish solved the challenges in electroless nickel/immersion gold and reduced cost without affecting the performance.

Citation

Mohamed Anuar, R.A. and Osman, S.A. (2021), "The formation of intermetallic layer structure of SAC405/Cu and SAC405/ENImAg solder joint interfaces", Soldering & Surface Mount Technology, Vol. 33 No. 2, pp. 75-85. https://doi.org/10.1108/SSMT-03-2019-0009