Development and Evaluation of a Preencapsulation Cleaning Process to Improve Reliability of HIC's with Aluminum Metallized Chips

With a view toward the use of aluminum metallized chips on hybrids, a preencapsulation cleaning process was developed and evaluated. The method involved the determination of the reactivity of Standard Bell System cleaning processes and reagents toward aluminum metallizations using continuity measurements. Substitutions for aggressive reagents were then sought. Evaluation of nonaggressive process sequences were carried out using ionograph measurements, quantitative carbon Auger analysis, and accelerated aging studies on purposely contaminated samples. It was determined that H2O2, alkali cleaners, and hot water are unacceptable for use. The use of a simple Freon degreasing step is inadequate. Introduction of a cold water rinse to effect removal of polar impurities is an improvement but not optimum. The Modified Plasma Cleaning Process (Freon, O2plasma, cold H2O) is the most effective clean of those evaluated. The O2plasma step is an effective component of the process. It does not increase the passivating oxide thickness. If a surface is clean, then the aluminum metallization will not corrode unless a new source of contamination is introduced.