INTERMETALLIC GROWTH IN LEAD-FREE SOLDERS ON PCB SUBSTRATESAuthors: K. Sweatman, S. Suenaga, and T. Nishimura
Company: Nihon Superior Co. Ltd.
Date Published: 9/25/2005 Conference: SMTA International
Lead does not form intermetallics with copper and tin remains a constituent of lead-free solders so that the basic composition of the interfacial intermetallic remains basically the same in lead-free assembly as that in tin-lead assemblies, mainly Cu6Sn5. However, some changes in morphology and growth rates can be expected. The widespread adoption of a nickelmodified tin-copper eutectic alloy as both a lead-free solder and a HASL finish introduces a new element with a reported effect on intermetallic behaviour into the system.
In this paper a study of the thickness, morphology and rate of growth in thermal cycling of the intermetallic at the interface between some widely used solders and finishes is reported with particular attention being paid to any effect of the nickel addition in the basic tin-copper eutectic.
Key Words: Intermetallic, PCB Finishes, Lead-free, HASL, tin-copper-nickel.
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