Wafer level packaging of silicon pressure sensors

In this paper, a new pre-packaging technique for silicon pressure sensors on the wafer level is presented. It is based on the use of UV photopatternable silicone which is deposited over the whole wafer by means of a novel device suitable for low-viscosity material coating and mask alignment. The process consists of the exposure of the deposited layer to UV light leading to cross-linking of the polymer according to the pattern of a chrome mask, which leaves the membrane area as well as the bonding pads free from silicone. After development and dicing, the chips are packaged and conventional wire bonding is performed. The area surrounding the UV photopatternable silicone pattern can then be filled with soft silicone gel for protection of the electrically active components against aggressive media. Results are presented for silicon piezoresistive pressure sensors on which 1.5-mm high octagonal wall structures of silicone elastomer have been patterned. Despite the thickness of the deposited layer, good resolution and aspect ratio are obtained, and the temperature dependence of the packaged pressure sensors is not influenced by the polymer layers.