Nondestructive Infrared Inspection of Hybrid Microcircuit Substrate-to-Package Thermal Adhesive Bonds

A method for nondestructive inspection of the thermal transfer effectiveness of adhesive bonds between the substrate and package (case) in the production of hybrid microcircuits is described. Because this bond is a series element in the thermal path for removal of the power dissipated by the microcircuit, its effectiveness is crucial to maintaining relatively low component-operating temperatures. As is well known, this can be directly equated to increasing reliability. Because the bonding material is between two opaque surfaces, it cannot be visually inspected. This situation motivated the work described here, which yielded the following results. 1) A nondestructive inspection technique employing infrared (IR) thermography was developed; the inspection can be performed in a production environment before the expensive step of completing wire bonding to the case has occurred. 2) The ability of the technique to distinguish between good and bad thermal bonds was demonstrated using two specially prepared test hybrids. 3) An analysis of the test method for use in planning inspection tests and interpretation of the test results was developed. The results show that this thermal imaging inspection technique affords a method to improve the quality of hybrid thermal bonding.