NDLI: Fluxless Sn-Bi-Au bonding process using multilayer design

Content Provider	IEEE Xplore Digital Library
Author	Choe, S. Chuang, R. Lee, C.C.
Copyright Year	2001
Description	Author affiliation: California Univ., Irvine, CA, USA (Choe, S.)
Abstract	For many years lead-free solders have been a topic of interest in the packaging industry. One possible substitute material among the lead-free solders is eutectic Sn-Bi alloy (42Sn-58Bi) which has a melting temperature of 139/spl deg/C. Earlier studies have shown that the conventional 63Sn-37Pb solder can be replaced by eutectic Sn-Bi in some low temperature applications. A fluxless alternative to the conventional soldering method is successfully developed using Sn-Bi-Au multilayer composite. The essence of this fluxless bonding technique comes from the spontaneous in situ formation of a thin AuSn/sub 2/ layer on the outer surface of the multilayer composite. This stable layer acts as a natural barrier against oxidation of the inner solder metals. The Sn-Bi-Au multilayer for bonding is prepared using a thermal evaporating vacuum chamber. The bonding temperature of this process ranges between 170/spl deg/C and 180/spl deg/C. The resulting as-solidified joint is made up of eutectic Sn-Bi alloy with small grains of AuSn/sub 2/ imbedded inside the solder. Sn-Bi joint cross-sections are examined to determine the quality of the joints. The process is found to be effective. SEM and EDX systems are used to examine the joint cross-section. The SEM images shows a uniform joint thickness of approximately 5 /spl mu/m. They also show the joint microstructure, exhibiting the usual lamellar structure of eutectic Sn-Bi alloy. EDX analysis also indicates the separation of the darker Sn-rich regions and the brighter Bi-rich regions. The fluxless feature, lead-free nature and processing temperature range of this bonding technique are particularly valuable for packaging photonic, optoelectronic, fiber optic, and MEMS devices and components.
Sponsorship	Components, Packaging, & Manuf. Technol. (CPMT) Soc. IEEE
Starting Page	486
Ending Page	488
File Size	255556
Page Count	3
File Format	PDF
ISBN	0780370384
ISSN	05695503
DOI	10.1109/ECTC.2001.927771
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2001-05-29
Publisher Place	USA
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Bonding processes Nonhomogeneous media Process design Environmentally friendly manufacturing techniques Lead Packaging Temperature distribution Soldering Oxidation Microstructure
Content Type	Text
Resource Type	Article
Subject	Electronic, Optical and Magnetic Materials Electrical and Electronic Engineering

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