Characterization of 0.6mils Ag Alloy wire in BGA package

Abstract

With cost erosion in semi-conductor business, manufacturing cost is becoming a real driving force for new trend. For Back End (BE), package cost is then one of the key to control the cost. For high I/O Wire Bond (WB) packages e.g. Quad Flat Packages (QFP), Ball Grid Arrays (BGA) etc., interconnect wires is one of the dominant portion on package cost, conventionally with gold (Au) wire. Despite Au wire is superior in bond-ability to different materials, soft mechanical properties for process workability and loop forming flexibility, the material cost and its market price fluctuation which giving big impact to product sales margin, is forcing the industry to look for alternatives. To respond this scenario, Bare Copper (Cu) and Palladium (Pd) Coated Copper are two of the successive substitutes which feasibility already proven and already industrialize. However, concerns and drawbacks have been raised up in terms of bonding quality, bonding process time, package limitations and reliability performance. A newly alternative material, Ag Alloy wire has been developed recently with its advantages of material and mechanical properties that similar to gold wire. Ag Alloy wire is now becoming latest technology trend that fully study as a potential alternative solution for gold wire bonding. Generally, characteristics and technical challenges of Ag Alloy wire must be well understanding and examining. This paper, intended to summarize the characterization of Ag Alloy wire in BGA package. The characterization covers (i) Capillary selection that focus on tools design based on fine pitch application requirement; (ii) Enhancement of forming gas control on free air ball formation; (iii) Process aspects (EFO; Base parameters) that fully optimized based on bondability and workability; (iv) Intermetallic (IMC) growth vs time on unmolded units to study behavior of Ag Alloy wire; (v) Reliability aspects on molded units at high temperature storage (HTS), thermal humidity storage (THS) and thermal cycle (TC) to verify and justify Ag Alloy wire reliability performance.