The Strength of High-Temperature Ag–In Joints Produced Between Copper by Fluxless Low-Temperature Processes

Abstract

Two copper (Cu) substrates were bonded using silver (Ag) and indium (In) and annealed at C to convert the joints into the solid solution (Ag) for enhanced strength and ductility. Cu-Cu pair was chosen so that the samples break in the joint during shear test. The upper Cu was electroplated with 15 lm Ag. The lower Cu was plated with 15 lm Ag, followed by In and 0.1 lm Ag to inhibit indium oxidation. Two designs were implemented, using 8 lm and 5 lm In, respectively. The Cu substrates were bonded at 180 C in 100 mTorr vacuum without flux. Afterwards, samples were annealed at 200 C for 1000 h (first design) and at 250 C for 350 h (second design), respectively. Scanning electron microscope with energy dispersive X-ray analysis (SEM and EDX) results indicate that the joint of the first design is an alloy of mostly (Ag) with micron-size Ag 2 In and (f) regions, and that of second design has converted to a single (Ag) phase. Shear test results show that the samples are very strong. The breaking forces far exceed requirements in MIL-STD-883 H standards. Fracture incurs inside the joint and is a mix of brittle and ductile modes or only ductile mode. The joint solidus temperatures are 600 C and 900 C for the first and second designs, respectively.

The growth and stress vs. strain characterization of the silver solid solution phase with indium

“…During the previous research, the authors have identified two major intermetallic compound, namely Ag 2 In and AgIn 2 [10]. Recently, our research group has successfully converted almost all of those intermetallic compounds into silvereindium solid solution phase [11], which is designated as (Ag)exxIn in this paper. The experimental results show that the properties of the bonding joint with (Ag)exxIn phase are intriguingly great.…”

Solid solution softening and enhanced ductility in concentrated FCC silver solid solution alloys

“…With the fast development of integrated circuit (IC) industries, electronic manufacturing and packaging activities have already grown into a global market of hundreds of billions of dollars per year. Recently, silver-based solid solution alloys have been widely considered as an alternative of interconnection materials in electronics manufacturing and packaging applications, such as die-attachment [6,7] and wire-bonding [8,9]. The mechanical properties are crucial to the manufacturability of the materials and long-term reliability of the whole electronic system.…”