Investigation of seal frame geometry on Sn squeeze-out in Cu-Sn SLID bonds

Cu-Sn SLID is an increasingly popular bonding technique with applications in such as hermetic sealing of microbolometers. A moderate bonding pressure is necessary to compensate for the surface roughness of the electroplated layers and to break the Sn oxide layer, thereby reducing the risk of voiding. However, such bonding pressures increase the risk for Sn squeeze-out during the bonding process, which has the potential to destroy MEMS or ROIC devices. To prevent this potential issue, an alternative bondline geometry consisting of 3x50µm wide bond rails and 25µm wide gaps was manufactured and compared to a continuous 200µm bondline by using nondestructive IR imaging, cross-sectional microscopy, and die-shear testing. High shear strength values of 31±9MPa and 43±18MPa were obtained for continuous and railed seal frames respectively. The Sn squeeze-out distance beyond the intended bondline was, on average, reduced by 60% when the railed geometry is employed. A reduction in peak squeeze-out distance from 188µm to 54µm was also observed.