Evaluation of polymer wafer bonding with silicone adhesive and patterned trenches

In the fabrication of system-in-package (SiP) devices, wafer bonding is a common yet very important process. The technologies widely used nowadays for wafer bonding include direct wafer bonding and intermediate layer bonding. Fusion bonding, one of the direct wafer bonding techniques, requires a processing temperature up to 800-1000°C to create strong covalent bonds between wafers. Some devices, however, cannot withstand such high temperature. Also, the stress generated due to different coefficients of thermal expansion is directly associated with the bonding temperature. Therefore, a low temperature wafer bonding technique is in demand. In this study, an innovative adhesive bonding method is proposed. Patterned trenches are fabricated on one side of the wafer and completely filled with silicone adhesive. The proposed wafer bonding method has several advantages over the traditional adhesive boning method. The trenches provide air escape paths. It also enchances the adhesion strength of the bonded wafers. Test vehicles are fabricated to demonstrate the proposed wafer bonding method with trenches. Shear tests are conducted to measure the mechanical performance of the proposed method. Results show that, when the sample is sheared perpendicularly to the trenches, the shear strength of the sample is 25% higher than that of the sample without trenches.