Flip chip as an enabler for MEMS packaging

With the recent trends in microelectronics to move more and more towards incorporating MEMS (micro electro mechanical systems) structures, lowering the overall cost becomes vital. One major cost driver in today´s MEMS is the packaging. Many of the MEMS structures require some level of low pressure for full quality operation, and some may even need vacuum to function properly. Different MEMS packaging strategies exist on the market and they can be divided into two different approaches. The first one protects the wafer temporarily during wafer scribing or dicing and the second one provides a permanent seal to the wafer through full wafer bonding before scribing and dicing. The latter, permanent methods allows for selecting very low cost packaging without hermeticity as a requirement, whereas in the temporary seal methods the seal is removed after dicing and the sensitive structures become unprotected again. Using flip chip for MEMS has the benefit of providing MEMS structures with a covering lid, the chip itself. A number of flip chip MEMS interconnection methods presented in literature are described.