Tin-based solder bonding for MEMS fabrication and packaging applications

This paper presents a tin-based solder bonding technology for microelectromechanical systems (MEMS) fabrication and packaging applications. Electroplated tin on a lithographically patterned seed layer of chrome–gold was used for bonding two Pyrex substrates. Average values of the tensile strength and the shear strength obtained were 14.6 MPa and 5.78 MPa, respectively. Shear strength data were analysed using Weibull statistics, which revealed presence of multiple failure mechanisms and an average value of β greater than 3. Failure occurred not only at the tin–tin bond interface but also at the tin–chrome interface. Highest values for the bond strength were obtained when the samples failed due to delamination at the tin–tin bond interface. Acoustic images of the bonded interface were used to qualitatively study the degradation in the bond interface when subjected to tensile stresses. Hermetic testing of the samples using a conventional He-leak detector showed leak integrity of better than 1 × 10 −11 mbar l s −1 .