Conductive Adhesives containing Ag-Sn Alloys as Conductive Filler

Abstract

Ag filled isotropic conductive adhesives (ICA) have been investigated as promising altenatives for lead containing solders in surface mount technology (SMT) applications; however, one serious concern is the ionic-mgration of the silver filled in the ICA, especially when used in high density interconnection assemblies. In his study, ionic-gration resistance and the contact resistnce of the ICA containing Ag-Sn alloy conducfive fillers were evaluated It was found that ionic-migrabon resistance depended on the Ag-Sn ratio and that Ag-Sn alloys containing 25 to 75 mol% of Sn had excellent ionic-migration resistance though their contact resistance was rather high, compared with silver. For the compatibility of the ionicn-migration resistance with lower contact resistance, and to undastand the effect of a Sn-Bi alloy powder mixture, several additives and polymer matrixes were also stxdied. New ICAs including these additives and a conventional ICA (as reference) werex evauated for SMT. Chip components with Sn plated termintions for stability in both contact resistance and adhesion strength were monitored during reliability tests. From the test results, it can be concluded that the new ICA is a potenfial material for SMT applications. Moreover, if mount loading was not sufficient and/or mount alignmient was not suitable, initial contact resistance was unstable. Therefore, we selected materials with reduction effect and we dereased the Sn ratio as low as we could The filler content rate was also increased. As a result the loading dependence was decreased.We were sucessful in keeping contact resistance more stable while maintning good ionic-migration resistance.

Isotropic conductive adhesives in electronics

“…Sancaktar et al (2004) have recently correlated electromigration with Ag surface pitting, and there also appears to be a field threshold (Mo, 2005). Systematic study is required to establish the boundaries to the effect (Manepallis et al, 1999), which is minimized by the use of high-purity Ag (with <10ppm Cu (Detert and Herzog, 1999), or Sn-Ag alloys (Suzuki et al, 2004;Toida et al, 2005) as sn appears to inhibit migration. Ag migration is evident in un-cured material , but it is not a problem in commercial products where it has been suggested that additives to the polymer seal the silver surface, defeating migration tendencies.…”