Leonel R. Arana

Ceramic Via Wafer-Level Packaging for MEMS

We will present a novel approach to wafer level packaging for micro-electro-mechanical systems. Like most common MEMS packaging methods today, our approach utilizes a wafer bonding process between a cap wafer and a MEMS device wafer. However, unlike the common methods that use a silicon or glass cap wafer, our approach uses a ceramic wafer with built-in metal-filled vias, that has the same size and shape as a standard 150 mm silicon wafer. This ceramic via wafer packaging method is much less complex than existing methods, since it provides hermetic encapsulation and electrical interconnection of the MEMS devices, as well as a solderable interface on the outside of the package for board-level interconnection. We have demonstrated successful ceramic via wafer-level packaging of MEMS switches using eutectic gold-tin solder as well as tin-silver-copper solder combined with gold thermo-compression bonding. In this paper, we will present the ceramic via MEMS package architecture and discuss the associated bonding and assembly processes.Copyright

Wafer Level Bonding of MEMS Devices Using Ceramic Lids

Wafer level bonding of MEMS devices is becoming an important packaging technique for small die. Wafer lid bonding simplifies and provides an economical assembly process. One requirement for RF MEMS devices is a hermetic lid, seal material, and sealing process for device reliability. A challenge of this packaging technique is the difference between the lid material CTE, coefficient of thermal expansion, and the silicon device wafer. We selected low temperature co-fired ceramics, LTCC, to evaluate as a potential MEMS lid material for wafer level bonding. This report covers the use of LTCC ceramic lids having CTE values of 5.5, 4.0, and 3.4ppm with thickness of 0.5 and 0.3mm. Different bonding recipes using an inert atmosphere were developed to manage warpage after bonding. Cooling ramp rates, dwell times at elevated temperatures, and lid scoring methods were investigated. A hold time at an elevated temperature was required for the ceramic lids with higher CTE values. With the low CTE ceramic lids, no hold time was required. We found successful RF MEMS wafer level bonding, WLB, can be achieved using low CTE ceramic lids.Copyright