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

Abstract

PurposeThe 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/approachSn-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.Findingsß-(Au,Ni,Cu)10Sn phase is formed during the soldering process. The IMCs evolution has two periods during the aging. The first is theξ-(Au,Ni,Cu)5Sn,ξ-(Au,Cu)5Sn andδ-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 toξ′ phase when the aging time extends to 250 h, and transformed toε-(Au,Ni,Cu)Sn2andη-(Au,Ni,Cu)Sn4after 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/valueThe results in this study have a significant meaning for the application of the new Sn-5Sb-1Cu-0.1Ni-0.1Ag in harsh conditions.