Microstructure evolution of Au/SnSb-CuNiAg/(Au)Ni during high temperature aging

Abstract

Purpose

The purpose of this paper is to investigate the morphology evolution and the composition transformation of Au-Sn intermetallic compounds (IMCs) of the new Au/Sn-5Sb-1Cu-0.1Ni-0.1Ag/(Au)Ni solder joint during the high temperature aging.

Design/methodology/approach

Sn-5Sb-1Cu-0.1Ni-0.1Ag solder balls (500 µm in diameter), heat sink with structure of 7.4 µm Au layer on 5 µm Ni-plated Cu alloy and Si chip with 5.16 µm plated Au were used to fabricate micro-solder joints. The joints were performed in a furnace at 150°C for 150, 250 and 350 h aging. The samples were polished and deep etched before analyzed by metallographic microscope and scanning electron microscopy, respectively. Energy dispersive x-ray spectroscopy was used to identify the composition of the IMCs.

Findings

ß-(Au,Ni,Cu)₁₀Sn phase is formed during the soldering process. The IMCs evolution has two periods during the aging. The first is the ξ-(Au,Ni,Cu)₅Sn, ξ-(Au,Cu)₅Sn and δ-AuSn were formed and grew to form a full-compound joint after about 150 h aging. The second is the conversion of the full-compound joint. The IMCs converted to ξ′ phase when the aging time extends to 250 h, and transformed to ε-(Au,Ni,Cu)Sn₂ and η-(Au,Ni,Cu)Sn₄ after 350 h aging. The thicker gold layer and thinner solder joint can promote the growth of the IMCs. ß-(Au,Ni,Cu)₁₀Sn emerged in Au/SnSb-CuNiAg/(Au)Ni in this research, which is not usually found.

Originality/value

The results in this study have a significant meaning for the application of the new Sn-5Sb-1Cu-0.1Ni-0.1Ag in harsh conditions.

Citation

Han, B., Sun, F., Li, T. and Liu, Y. (2020), "Microstructure evolution of Au/SnSb-CuNiAg/(Au)Ni during high temperature aging", Soldering & Surface Mount Technology, Vol. 32 No. 2, pp. 57-64. https://doi.org/10.1108/SSMT-04-2019-0015