Evaluation of Removal Rate of Cured Silicone Adhesive from Various Electronic Packaging Substrates by Solvent and Silicone Digesters for Rework Applications

Reworking electronic packages is an integral process related to diagnostics and salvaging valuable materials. It is a meticulous and time-consuming procedure that requires some knowledge of the package material composition to determine compatible cleaning solutions and processes. Silicone adhesives are being used more frequently due to their ability to minimize shear stress during temperature cycling. A common method for removing silicone adhesive is by swelling in solvent and removing by mechanical methods taking care not to damage fragile materials and leave minimal residue. Silicone digesters (emulsifiers) are another means of removing cured silicone. They are comprised of weak acids or bases and remove silicone by breaking the siloxane bonds that make up the polymer matrix. They are able to penetrate into areas that are difficult, or impossible to reach, greatly reducing the risk of causing damage due to mechanical removal. The purpose of this study is to evaluate the rate of silicone removal by solvents and silicone digesters on silicones bonded to copper and aluminum. The removal rate was determined by developing a rating system based on time intervals where silicone was observed to delaminate or dissolve. Silicone adhesives and Thermal Interface Materials (TIMs) were used in the evaluation of two commonly used solvents and two commercially available silicone digesters. Copper and aluminum panels were evaluated by using a ~ 0.5 mm thick layer of silicone to bond 2 panels together. The samples were placed in cleaning solution for 24 hours at 40 degree Celsius and evaluated at specific intervals for any changes in appearance of silicone. Based on the performance of combinations of silicone, substrate and cleaner, the engineer can chose which method is best for reworking based on their own assembly configuration and materials.