Effect of Surface Finish of Substrate on Mechanical Reliability of in-48SN Solder Joints in Moems Package

TL;DR

This study investigates how different substrate surface finishes affect the interfacial reactions and shear strength of In-48Sn solder joints in MoEMS packages, revealing that surface finish significantly influences joint reliability.

Contribution

It provides a comparative analysis of four substrate surface finishes and their impact on intermetallic formation and mechanical strength of In-48Sn solder joints.

Findings

In-48Sn/I-Ag solder joints exhibit the best shear properties.

ENIG surface finish results in the weakest mechanical integrity.

Distinct intermetallic compounds form at different interfaces.

Abstract

Interfacial reactions and shear properties of the In-48Sn (in wt.%) ball grid array (BGA) solder joints after bonding were investigated with four different surface finishes of the substrate over an underlying Cu pad: electroplated Ni/Au (hereafter E-NG), electroless Ni/immersion Au (hereafter ENIG), immersion Ag (hereafter I-Ag) and organic solderability preservative (hereafter OSP). During bonding, continuous AuIn2, Ni3(Sn,In)4 and Cu6(Sn,In)5 intermetallic compound (IMC) layers were formed at the solder/E-NG, solder/ENIG and solder/OSP interface, respectively. The interfacial reactions between the solder and I-Ag substrate during bonding resulted in the formation of Cu6(Sn,In)5 and Cu(Sn,In)2 IMCs with a minor Ag element. The In-48Sn/I-Ag solder joint showed the best shear properties among the four solder joints after bonding, whereas the solder/ENIG solder joint exhibited the weakest mechanical integrity.