Nonmigration conductive adhesive

Abstract

Ag filled isotropic conductive adhesives (ICAs) have been investigated as promising alternatives for lead-containing solders in surface mount technology (SMT) application. However, one serious concern is the electro-migration of the silver filled in the ICAs, especially when used in high density interconnection assembly. In the present study, electro-migration resistance and contact resistance of ICAs containing Ag-Sn alloys as conductive fillers were investigated. It was found that electro-migration resistance depended on the Ag-Sn ratio and that Ag-Sn alloys containing 25 - 75 mol% of Sn had excellent electro-migration resistance though their contact resistance was rather high, compared with silver. To improve their contact resistance, a mixture of Ag-Sn alloy and Sn-Bi alloy was also investigated. The mixture effectively combined electro-migration resistance with lower contact resistance. These new ICAs and conventional ICAs (as reference) were evaluated for SMT, using chip components with several kinds of terminations for their stability in both contact resistance and adhesion strength during reliability tests. From the test results, it can be concluded that the new ICA is potential material for SMT application.