Evaluation of Electrically Insulative Adhesives for Use in Hybrid Microcircuit Fabrication

Although it is generally accepted that the use of adhesives in the fabrication of hybrid microcircuits offers advantages over other bonding methods, there currently does not exist a set of guidelines for the selection of adhesives which will ensure sufficient compatibility with microcircuit components and metallization systems to meet the long use-life, high-reliability requirements of military and space applications. The initial results of a study directed to the task of selecting suitable evaluation tests which can form the basis for such guidelines for electrically insulative adhesives are presented. The properties of adhesives considered to be of major importance for the proposed application are enumerated and briefly commented on. Polymeric types of adhesives are briefly reviewed and the major epoxy resin-curing agent systems comprising the adhesives that are commercially available and represented as being specifically designed for microelectronic use are identified. Specific tests to determine the chemical and electrolytic corrosivity of adhesives to commonly used metallization systems, their long term outgassing after cure, and their bond strengths under a variety of conditions are defined and discussed in detail. Comparative results obtained to date from these tests are given for five representative adhesives. All are epoxies cured with a different major type of curing agent: a primary secondary amine, a tertiary amine, an anhydride, a modified heterocyclic amine, and a boron trifluoride complex.