Advancements in Silver Wire Bonding

Abstract

Silver is a leading competitor to gold and copper in fine pitch wire bonding used in the interconnection of microelectronic devices. Primary material for wire bonding has been gold, which gave way to copper in order for original equipment manufacturers to realize cost benefits. However, copper wire bonding has exhibited several reliability issues, especially in industrial and high temperature applications. Corrosion is the major problem, which was mitigated by coating the wire with palladium, which increased overall cost of production. Other concerns include harder free air ball (FAB) leading to under pad metallization cracking, smaller process window, excessive aluminum splash especially in fine pitch bonding, and lower throughput and yield arising from the hardness and stiffness of copper. Due to the above concerns, automotive, military and aerospace industries are still reluctant to fully adopt copper wire bonding. Light emitting diodes (LEDs) are also not manufactured with copper wires due to its low reflectance. Some of these industries are still using gold wire bonds in most of their packages, but are continually looking for an alternative. Silver wire bonds have good electrical and thermal conductivity, are less prone to corrosion than copper, have low melting points and comparable hardness to gold. Also, cost of silver has been shown to be similar to that of palladium coated copper wire, hence making it a good alternative. Silver wire bonding, a relatively new area of research, has attracted a lot of research focused on wire dopant material, bonding process, quality and reliability. This paper is aimed to serve as a comprehensive review of research done in this area, by summarizing the literature on silver wire bonding, establishing benefits and drawbacks over other wire bond materials and indicating reliability concerns along with failure modes and mechanisms.

Research Progress on Bonding Wire for Microelectronic Packaging

“…Cu bonding wire, as an alternative wire, has a potential to provide good electrical connections for high-power and highly-integrated electronics because of its higher electrical and thermal conductivity and lower cost than Au [ 13 , 14 , 15 ]. However, since the Cu bonding wire has the properties of high hardness and oxidation rate and complex bonding process that will lead to damage of pad during bond, scholars agree that Cu bonding wire is not the ultimate candidate for Au bonding wire [ 16 , 17 , 18 ]. Ag bonding wire attracts the attention of scholars because of its excellent electrical and thermal conductivity and lower price than Au.…”

Metallographic Mechanism of Embrittlement of 15 μm Ultrafine Quaternary Silver Alloy Bonding Wire in Chloride Ions Environment

“…Wire bonding is the most widely used technology in the electronic packaging industry [ 1 , 2 , 3 ]. Previously, gold wire was the most commonly used material in wire bonding, but with the high price of gold, many alternative materials have been proposed [ 4 , 5 , 6 ]. Currently, the alternative materials with the most potential are copper-based and silver-based wires [ 7 , 8 , 9 , 10 ].…”

Effects of Process Parameters on Bond Properties of Ag-2.35Au-0.7Pd-0.2Pt-0.1Cu Alloy Wire

“…Cu bonding wire is a preferred alternative material because of its lower cost, slower intermetallic growth on Al pads, and higher thermal conductivity and mechanical strength compared with Au bonding wire [ 10 , 11 , 12 ]. However, researchers agree that Cu bonding wire is not the definitive substitute for Au bonding wire due to its high hardness and oxidation rate and complex bonding process that will result in pad damage during bonding [ 13 , 14 , 15 ]. Ag bonding wire, as a promising material for the development trend of microelectronic packaging with high density, high integration, and high speed, has lower cost, better manufacturability, and higher reliability than Au and Cu bonding wires [ 16 , 17 , 18 ], and it has been utilized in integrated circuit (IC) and light-emitting diode (LED) packaging [ 19 , 20 , 21 ].…”