SBIR Phase I: Selective Wafer Bonding for Wafer-Level Packaging of Microelectromechanical Systems (MEMS) and Related Microsystems

This Small Business Innovation Research (SBIR) Phase I project addresses selective laser-assisted bonding for wafer-level and chip-scale vacuum packaging of Microelectromechanical Systems (MEMS) and related Microsystems. This novel method is especially suitable for vacuum bonding wafers containing devices with low temperature budgets and for managing stress distribution. Furthermore, sealed, encapsulated and released wafers can be diced at the wafer scale without damaging the MEMs devices, thus offering tremendous economies of scale useful toward commercialization. Low temperature solder, such as Pb37/Sn63, will be used to bond silicon chips and wafers using a continuous wave carbon dioxide (CO2) laser. Optimum values of pertinent process parameters and the capability to produce high quality bonds at representative scales will be determined. The study will include both lead-tin solders and lead-free solders. The bonding process will be performed in a vacuum chamber at a pressure of less than ten milliTorr to achieve fluxless soldering and vacuum encapsulation of silicon dies. While the bonding temperature at the sealing ring will be close to the reflow temperature of the eutectic lead-tin solder (183 degrees), the global average temperature will be considerably lower due to the localization of the laser heating. This factor will be critical for many MEMS devices, such as those containing stress sensitive radio-frequency (RF) MEMS, optical devices and low temperature biomaterials. Today, 60 percent of the cost of MEMs products is due to special packaging requirements and lack of standardization. MEMs packaging is far more challenging than traditional packaging, and presents technical and cost barriers. This work will develop MEMs packaging to meet the needs of this important segment of the rapidly growing $20B packaging industry. The goal is to have several new wafer level packaging platforms demonstrated and ready to insert into high-volume manufacturing lines when the market starts to regain strength.