Stability of AuSn eutectic solder cap on Au socket during reflow

Abstract

The stability of Au20Sn eutectic cap formed during reflow of Sn/Au bump was studied under multiple reflow cycles. For a 5 mu m thick Sn layer, the eutectic caps formed for the bumps of 60 and 40 mu m in diameters were quite stable up to 10 reflows and the zeta compound layer at the interface was a good barrier layer to prevent the exhaustion of the eutectic solders. However for 20 mu m bumps, the relative larger eutectic volume resulted in side wall wetting. Therefore only small part of eutectic alloy was left on the top of the Au socket after one reflow. After three reflows Au socket was almost covered by a single zeta compound layer. The results identified that the maximum cap height formed during reflow should be smaller than half of the bump diameter to maintain it on the Au socket

Temperature-Dependent Structural Evolution in Au44Ga56 Liquid Eutectic Alloy

“…Au and Au-based alloys are widely used as high-temperature solders for bonding in microelectronic and optoelectronic package despite its high price. − Ga, possessing a low melting point (about 303 K), could be a good additive to reduce the melting points of Au-based solders . In the Au-Ga system, the diffusion coefficient of 198 Au in liquid Ga shows a considerably higher activation energy below 500 K than above it in the studied temperature range of 308–733 K .…”

Three dimensional interconnects with through silicon vias and electroplating solder microbumps

“…This is an option for low cost maskless process for UBM fabrication, electroless Ni-P in combination with immersion Au deposition. Besides, ENIG formation does not require any high vacuum or photolithography equipments to form the metal stack on top of the bond pads, therefore it is a simple and low cost solution for high density and high pin-count buildup IC packages [8]. Figure 3 shows a cross-sectional view of TSV and UBM pad.…”

Interfacial Microstructure and Mechanical Properties of Titanium/Sapphire Joints Brazed with AuSn20 Filler Metal

“…Adding low-melting-point elements (In, Sn, Ga, Bi) [27,28] to the solder alloy to reduce the connection temperature can be used to relieve residual stress. AuSn20 (wt.%) eutectic filler is widely used in the electronic packaging and medical device industry due to its good biocompatibility, low melting temperature (278 • C), high thermal conductivity, excellent corrosion resistance, and many other advantages [29][30][31][32][33][34][35]. Therefore, AuSn20 solder was used to braze to ensure the mechanical property and biocompatibility of the brazed joints.…”