The Microelectronic Assembly Of High-performance Silver Conductive Adhesive

Based on methyl-hexahydro-phthalic anhydride (MeHHPA) as curing agent and 2-ethyl-4-methylimidazole (2E4MZ) as catalyst, the key factors and their effects on the conductive performance, adhesion strength and reliability under high temperature and high humidity environment of electrically conductive adhesive (ECA) were stuied by using different kinds of epoxy resin, silver filler (flake or powder), additive and toughening agent.The curing procedure was determined by DSC. Micro mophorlogy of silver fillers and their distribution in the cured conductive adhesive were investigated by SEM. The curing shrinkage of the matrix without silver filler was also measured. The conductive performance, adhesion strength and aging performance under high temperature and high humidity environment were characterized by resistivity test, tensil shearing strength test and 85℃/85%RH aging test, respectively. The following results can be summarized.(1) The conductivity of ICA increased with the addition of silver flake and the tensil shearing strength decreased at the same time. The percolation threshold was at the point of 60wt% filler loading level, i.e. 14.7vol%, and the corresponding conductivity was 66.7 S·cm^-1.(2) With the same silver flake and equal loading level, the resistivity of conductive adhesive could be smaller when the matrix of adhesive had a larger curing shrinkage. The tensil shearing strength of ICA was determined by the molecular structure of epoxy resin, exhibiting decreasing with the increase of curing shringkage. With the same filler loading level, the silver flake with the larger diameter thickness ratio had better conductive performance. But the tensil shearing strength was smaller as the establishment of conduvtive network deteriorated the frame structure of matrix. When filled with the blend conductive filler of silver flake and silver powder, the conductivity could be improved because the addition of silver powder facilitaed the contact of silver flakes. The proper mixing time varied with different conductive adhesive. It was found that not all the conductive adhesive could reach their best conductive performance only by changing the mixing time.(3) The L9 (3⁴) orthogonal experiment indicated that the addition of proper level of additives evidently improved conductive performance, adhesion strength and the contact resistance aging performance of conductive adhesives when under 85℃/85%RH aging environment. The contact resistance of conductive adhesive without additive was not stable after a certain aging time. But the effect of additive on the tensil shearing strength aging test was not so remarkable, which might result from that the metal for adhsion test was aluminium and was easier to be corroded than copper used in the contact resistance aging test.(4) With the addtion of carboxyl-terminated butadiene acrylonitrile (CTBN) , the tensil shearing strength of matrix increased, the tensilshearing strength of conductive adhesive decreased and the conductive performance was impaired. The pre-reaction route could effecively toughen the matrix, but deteriorated the conductive performance at the same time. The route without pre-reaction only softened the matrix and had no obvious impairment of the conductive performance.(5) The effect of prepolymer polyurethane (PPU) on the performance of conductive adhesive is similar to the CTBN. With the addition of 15wt% PPU, the tensil shearing strength increased but the conductivity decreased.