Si based multi-layered print circuit board for MEMS packaging fabricated by Si deep etching, bonding and metal powder injection

In this report, Silicon wafer based multi-layered print circuit board is presented. The developed stacked circuit board will lead to realization of 3 dimensional MEMS packaging. The through holes and trenches were formed by ICP Si deep etching and the stacked layered structure was prepared with Si fusion bonding of ICP etched wafers. Metal was filled into ICP fabricated through holes and trenches to make electrical feed through. Four Silicon wafers with ICP through holes are aligned and successfully joined by fusion bonding. The target application of this work is multi-layered Silicon based print circuit board. The electrical feed through was fabricated by injecting the Ag (80 wt%) + Cu(20 wt %) mixed with binder, low melting temperature metal, and Ag electrical conductive paste into the small diameter through holes and trenches in oxidized Silicon wafer stacked structure. A multi-component binder system comprising of EVA (Ethylene Vinyl Acetate 35 wt%) + PW (Paraffin Wax 65 wt%) was used. Super critical debinding method is applied prior to final sintering process. The ratio of metal powder and binder was optimized. Low melting point metal and electrical conductive paste filling methods were also tried by injection and vacuum extraction. SEM observation shows that the through holes are filled with metal for a single wafer. However we have still difficulty in filling the metal into four wafers stacked layer. The electrical conductivity test was sufficient between top and bottom. Several feed through formation methods have been proposed.