Multifunctional coatings for wafer-level chip scale packaging

For advanced wafer-level chip scale packages (WLCSP), board level solder joint reliability is a major concern, and typical stress-relieving methods such as capillary underfills and molding compounds are costly. One method of low cost reliability improvement for WLCSPs is the use of a wafer level SolderBrace^trade coating, which delivers improved reliability with minimal material and capital cost. In this presentation, several new SolderBrace materials are characterized and screened for their use in two different application methods. Processing of the SolderBrace coating can be achieved by two methods. The first is similar to that of polyimides: spin coat, bake, photo-image, solvent develop, and ball drop. The second application process involves printing the material on the already-balled wafers followed by solder cleaning and cure. Unlike polyimides, these coatings are low temperature cured, have low CTE values (13-18ppm), and have minimal wafer bow. These properties make a SolderBrace coating attractive as an alternate passivation coating, while also functioning as a partial underfill SolderBrace coatings are thermally, mechanically, and chemically robust, offering a unique method to package low cost high performance WLCSPs.