Correlation of silver migration to the pull out strength of silver wire embedded in an adhesive matrix

The substantial growth in the electronics industry has created a need for environmental and user-friendly alternatives to tin/lead (Sn/Pb) solders for attaching encapsulated surface mount components on rigid and flexible printed circuit boards (PCBs). Electronically conductive adhesives (ECAs) have been explored in this manner to establish mechanical as well as electrical joints between PCBs and surface mount components. Applications of conductive adhesive are limited due to serious concerns associated with the long-term reliability data of current commercial ECAs. One critical concern in wire bonding applications is the significant decrease in the bond strength and consequent loss of the conducting properties of adhesive due to silver migration. In this study, an effort is made to understand and model long-term silver migration phenomenon with respect to different parameters (duration of the migration, dry and wet conditions), and pull-out strength of silver wire embedded in an epoxy adhesive matrix. Morphology of embedded silver wire after migration and pull-out was also studied using scanning electron micrographs. Migration area increased with the duration of migration, and reduction in the pull-out strength was significant in wet condition as compared to dry condition. The increase in migration area was consistent with the reduction in pull-out strength in both wet and dry conditions.