Preventing conductive white residue formation by modifying the manufacturing process

Soldering has long been the dominant means by which the electronic components are attached, mechanically and electrically to the circuits in which they will operate. The final step of the soldering process has traditionally been to clean the assemblies using an aggressive Chlorofluorocarbon (CFC) based cleaner to remove any "residue" which could retard electrical performance. Recently these cleaners have been banned by international convention requiring that the electronics industry look at the cleaning (and soldering) process in detail and identify ways to produce reliable electronics without using CFC cleaners. To explore every possible alternative to CFC cleaning, and make an evaluation is a complicated task, and could take years. This is beyond the scope of any one company who would have neither the time nor the funds to conduct such a detailed analysis. Such large-scale, detailed, exploratory work can be completed at an academic institution. However in the university environment one cannot typically verify their results in a "real" situation, as industrial guidance is necessary. Thus Boeing, Rensselaer, EMPF, and the Naval Air Warfare Center (NAWC) formed a collaborative project to address the cleaning problem. The challenge was to identify means by which conductive residue formation could be eliminated in the manufacturing environment-in the time period of one year. Simple experiments which simulated the wave soldering process were conducted at Rensselaer under the guidance of Boeing, EMPF, and NAWC. These results were assessed in a large-scale manufacturing environment at Boeing. By working together and pooling our strengths it was possible in a 15 month period to do the following. 1) Propose a two-step reaction mechanism describing residue formation in a humid environment. 2) Determine that controlling the fluxing reaction is likely to be the most effective way to reduce the likelihood of residue formation. 3) Examine the kinetics of residue formation in a humid environment. At the end of the paper ideas for future examination of this process are discussed, as is our evaluation of the collaboration. One benefit of such short-term collaborative efforts is that bachelors and masters level students and gain industrially significant experience at school. The results of this project are available on-line at http://saturn.vcu.edu/mapalmer/residue.