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Temporary Protective Packaging for Optical MEMS
Keywords: Temporary 0-level package, optical MEMS, polymer
The fragility of MEMS devices is one of the main concerns in case of standard packaging. Steps such as wafer dicing, die handling, assembly and wire bonding can seriously damage the device functionality if the MEMS is not properly protected during the assembly processes. In this paper we report for the first time on bonding and removal of protective temporary caps used to ease the packaging of MEMS for optical applications. The package, based on a heat decomposable and photo-patternable polymer sealing ring, is gross leak tight, fulfills the MIL spec for shear testing and respects the thermal budget of Al-coated SiGe micro-mirrors. The SiGe mirrors are unharmed after debonding the cap. After release of the micro-mirrors at wafer level, a temporary cap with patterned Unity 2203P is bonded to the device wafer, enabling dicing and following assembly of the die to a PCB. The assembly on the PCB can be done by wire bonding and the cap can finally be removed by applying heat. As Unity 2203P is a non-conventional photo-patternable material, the spin curve, exposure and baking conditions had to be defined and optimized. The protective caps are assembled using a die to wafer approach on a flip-chip bonder. The thermo-compression profile has been optimized with respect to shear strength, thermal budget and gross leak tightness. The caps are removed by thermal decomposition of the Unity film, leaving little residues in the patterned area. Debonding is done on the flip-chip tool, allowing a slow separation of the cap and MEMS wafer during heating. Several dies with released micro-mirrors were covered with temporary caps by using the optimized process. After dicing and debonding the mirrors were found to be unharmed. Optical and electrical measurements demonstrate the applicability of the process.
Lieve Bogaerts,
IMEC
Leuven, Flanders 3001,
Belgium


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