Study of 0.6mil silver alloy wire in challenging bonding processes

Abstract

With competitive price and superior electrical/thermal conductivity and mechanical properties, more and more IC package industries have adopted copper (Cu) and palladium coated copper (PdCu) wires as the alternative to gold (Au) wire in the past decade. However, the high hardness and the excessive ultrasonic energy and bonding motions required during bonding of Cu wire limit its usage in areas such as memory packages and sensitive devices that are prone to damages on the pads and under-layer dielectrics. Silver (Ag) and Ag-alloy wires emerge as other alternatives since they have similar properties like wire hardness, elongation and breaking load at room temperature as Au wire while having a more competitive price. Process capability of ultra-fine (0.6mil) Ag-alloy wire, including free air balls (FAB) and bonding capability on aluminum (Al) die pads were first investigated. Factors affecting the FAB performance were studied and optimum settings were recommended. Comparison of bonding responses between Au, PdCu and Agalloy wires on challenging scenarios, such as overhang dies and die-to-die bonding, were also included in the study. Benchmarked Au process, Ag-alloy wire possesses great portability and wide first bond process window. Ag-alloy wire also demonstrates good bonding capability and loop shape control on challenging applications, such as overhang die and long die-to-die applications. However, further optimization of Ag-alloy process is still necessary to overcome its constrains, such as higher hardness and higher energy required during bonding of Ag-alloy wire.