This is a common issue that integrated circuit assembly companies have experienced. Post mold final cure and bake out are accomplished in a batch process in an oven. Temperatures for this process can exceed 200 °C and in an air atmosphere, will lead to oxidation of the copper lead frames.
The best alternative that has been adopted is to use an inert atmosphere within the post mold curing oven. Most standard ovens for this process are not designed to use an inert atmosphere. There are several vendors that manufacture inert atmosphere ovens for this process. The ideal O₂ ppm level for this process is < 1000 ppm. At these O₂ ppm levels, one can achieve good final cure and eliminate the copper lead frames for oxidizing. The initial cost to replace the ovens may be slightly prohibitive, however your overall cost of ownership will be reduced, and the quality of the assembly will be enhanced, not to mention the elimination of potential environmental issues with copper oxide removal via acid etch and deionized water cleaning.
Air Products has a new offering, Intelligent Nitrogen Control System (INCS), that can monitor the O₂ ppm levels in the curing oven and maintain a consistent O₂ ppm level while controlling the nitrogen gas consumed. Ask Air Products to evaluate your processes and how we can assist you in converting to an inert atmosphere post mold curing process.