Intermetallic growth behaviour of gold ball bonds encapsulated with green moulding compounds

The move towards lead-free microelectronics packaging assembly and environmentally-friendly packaging materials has prompted the need to replace Pb-Sn solders with Sn-Ag based systems that require higher peak reflow temperatures, as well as the elimination of bromine flame retardants from transfer moulding compounds. Alternative chemistries have been developed to replace Br-based flame retardants. However, the use of higher reflow temperatures has further burdened moulding compound suppliers by demanding that compounds withstand the additional stresses that occur in a lead-free reflow process. From the bonding wire manufacturer´s perspective, the use of the new compound chemistries is a concern because of the chemical complexity and highly reactive nature of compounds in the uncured state and their potential for corroding gold aluminide intermetallics. This article presents the results of a study conducted on the intermetallic growth of K&S gold ball bonding wires after high temperature storage (HTS) on bare and encapsulated devices. Two compounds were used, a commercially available green compound (compound A) and a compound manufactured in-house by Cookson (compound B). After HTS, compound A developed severe ball lifts, and exhibited erratic intermetallic growth after de-capping. Differences in the performance of each compound were attributed to corrosion due to the reactivity of additives in the compounds with gold aluminides