Fracture behavior of isotropically conductive adhesives

The fracture behavior of several commercial, silver-filled epoxies was stud ied using a combination of fracture mechanics, surface science, and microsc opy, Three-point bend tests revealed that the bulk fracture toughness of th e silver-filled epoxies fell with a narrow range 1.1-1.3 MPa-m(0.5). Both e lectron and optical microscopy studies indicated that crack path deflection due to the silver-particles was the primary micromechanical deformation me chanism. Surprisingly, the interfacial fracture energies between the epoxie s and a copper surface ranged from 50 to 900 J/m(2), Contact angle measurem ents on the cured epoxies indicated that some epoxy surfaces are more activ e than others. However, the correlation between thermodynamic work of adhes ion and fracture energy is rather weak and suggests only a modest trend. In summary, although the use of contact angles/surface energies to predict ad hesion is promising, much more effort is required to make it a reliable scr eening tool. Fortunately, the use of interfacial fracture mechanics can det ect differences in adhesive strength, and should allow packaging engineers to select die attach adhesives with improved adhesion.