Electrically insulative adhesives for hybrid microelectronic fabrication

The use of insulative adhesives for attachment of alumina substrates to metallic headers is gaining considerable interest in the areas of hybrid microcircuit fabrication. However, many unresolved problems concerning long-term reliability of hybrid circuits using organic materials continues to plague the industry. Thus, the purposes of the investigation described herein are: (1) to select and describe tests pertaining to long-term reliability and (2) to evaluate several insulative adhesives specifically formulated for the microelectronic industry, for the purpose of selecting a substrate attach adhesive for use in a high-rate hybrid production facility. Specific properties investigated include: lap shear and tensile strength, effects of temperature aging and cycling, effects of solvent exposure, degradation temperature, adhesive-adherent compatibility, and outgassing amounts and effects. The insulative adhesives selected for evaluation include: Scotchcast 281, a one-component premixed frozen paste; Ablefilm 550, a "B" staged epoxy-impregnated fiberglass film and Epo-Tek H74 and H77 both two-component systems requiring mixing prior to use. Selection of these adhesives for evaluation was partially based on the results of a literature survey, which revealed these adhesives to be representative of those currently in use for hybrid assemblies.