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Solder Brace Coatings for Wafer-Level Chip Scale Packaging
Keywords: wafer level adhesive, solder bracing, wafer level underfill
For 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 solder brace coating, which delivers improved reliability with minimal material and capital cost. In this presentation, the process of using a highly filled, photo-definable coating will be discussed. Spin-coat application of the material onto wafers forms a photo-definable polymer layer that reinforces the solder joints. Processing of the solder brace coating is similar to that of polyimides: spin coat, bake, photo-image, solvent develop, and cure. Unlike polyimides, these coatings are low temperature cured, have low CTE values (18-20ppm), and have minimal wafer warpage. These properties make a solder brace coating attractive as an alternate passivation coating, while also functioning as a partial underfill. Partial underfills are known to offer improvements in thermal cycling and drop reliability. Solder brace coatings are thermally, mechanically, and chemically robust, offering a unique method to package low cost high performance WLCSPs.
Candice Brannen, Senior Scientist
LORD Corporation
Cary, NC

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