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

In our previous works, metal injection technique into small diameter (10 -100 μm) through holes was developed and applied for fabrication of Si based print circuit board. In the present work, we present the metal filling technology by vacuum casting into 3 dimensional through holes and trenches structure fabricated in stacked layered Si wafers prepared by fusion bonding of ICP etched Si wafers. Metal electrical feed through was successfully prepared by the method. Conventional print circuit boards have been fabricated with Epoxy resin based materials. In recent years Si is regarded as a candidate for next generation materials for print circuit board substrates, as the substrate whose thermal elongation same as the mounted chips is an ideal solution to residual stress problems in the elevated temperature application. In this report, we developed the double sided mountable stacked circuit board using Si deep etching technology and fusion bonding. This technology is expected to lead to the realization of the assembling of sensors, actuators and ICs, i.e. 3 dimensional MEMS packaging. In this report, we adopted micromachining technology to this application area and the special emphasis is placed on the low cost and reliable process development. The detailed items to be developed are shown as follows; (1) Development of Si wafer through holes penetration and trench formation by ICP etching. (2) Alignment and bonding of micromachined wafers. (3) Development of insulating layer with oxidation. (4) Development of formation of electrical feed through for stacked layers.