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.

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