NDLI: Very High-Temperature Joints Between Si and Ag–Copper Substrate Made at Low Temperature Using InAg System

Content Provider	IEEE Xplore Digital Library
Author	Jong Sung Kim Wang, P.J. Lee, C.C.
Copyright Year	1999
Abstract	We present a fluxless bonding process between silicon and Ag-copper dual-layer substrate using electroplated indium/silver solder. The nucleation mechanism of In plated over Ag layer is first investigated. It is interesting to discover that In atoms react with underlying Ag to form AgIn₂ compound layer during electroplating. A novel Ag laminating technique on Cu substrates is developed. The Ag cladding functions as a strain buffer to manage the large mismatch in coefficient of thermal expansion (CTE) between semiconductors such as Si (3 ppm/degC) and Cu (17 ppm/degC) substrates. To bond Si chips to the Ag layer on copper substrates, In-based alloy (InAg) is used. A fluxless bonding process is developed between Si/Cr/Au/Ag and Cu/Ag/In/Ag. The process is performed in 50-militorr vacuum to suppress solder oxidation. No flux is used. The resulting joints consist of three distinct layers of Ag, Ag₂In and Ag. Microstructure and composition of the joints are examined using scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDX). Bonded samples are further annealed to convert the Ag₂In phase into solid solution phase (Ag). The joint has a melting temperature above 850degC. This technique presents our success in overcoming the very large CTE mismatch between silicon and copper. It can be applied to mounting numerous high-power silicon devices to Cu substrates for various industrial applications.
Sponsorship	IEEE Components, Packaging, and Manufacturing Technology Society
Starting Page	782
Ending Page	789
Page Count	8
File Size	2227798
File Format	PDF
ISSN	15213331
Volume Number	31
Issue Number	4
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2008-12-01
Publisher Place	U.S.A.
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Temperature Substrates Copper Bonding processes Silicon Thermal management Scanning electron microscopy Indium Silver Atomic layer deposition laminating Ag annealing Cu substrate fluxless bonding high-temperature joint In
Content Type	Text
Resource Type	Article
Subject	Electronic, Optical and Magnetic Materials Electrical and Electronic Engineering

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