Bulk properties of the metal are hard to come by because everything Micross does is custom. You can check with @jeffdi about what the layer specifications are that we put on the form for submission to Micross. The redistribution metal layer is copper and I think is the default 3um thickness. This is sitting above a 5um polyimide layer. That's probably good for a rough approximation of the effect of the bump bonds. If you need any additional information, just let me know.