Patent ID: 7608485
Filing Date: 2009-10-27
Classification: H01L

Abstract:
1. A method for attaching Si circuit dies to heat sinks, wherein each of said dies is sawed from a wafer, comprising the steps of: reducing the thickness of said wafer by mechanical grinding; applying an isotropic wet chemical etching to a backside of said wafer to eliminate crystal defects; evaporating adhesion and diffusion barrier metals on the backside of said wafer; evaporating Au and Sn on the backside of the wafer, wherein the weight proportion of Au in relation to the total amount of Au and Sn evaporated on the backside of the wafer is equal to or larger than 85%; sawing the wafer into said circuit dies, and soldering each of said circuit dies to a respective heat sink; and wherein the Au is deposited adjacent the evaporated adhesion and diffusion barrier metals and has a thickness such that at least a portion of the Au remains solid and does not diffuse when the dies are soldered to the respective heat sinks.