Squeeze-out and bond strength of patterned Cu[sbnd]Sn SLID seal-frames

Abstract

Control of Sn squeeze-out due to the presence of liquid phase and bond pressure is important in CuSn SLID bonding. This work studies the impacts of seal-frame design for limiting this squeeze-out. Three alternative seal-frame geometries are evaluated and compared to a traditional continuous seal-frame with respect to squeeze-out and shear strength. The alternative designs include open spaces to accommodate squeeze-out and are: 1) One mating partner with 3 × 50 μm wide rails and 25 μm gaps. 2) Previous geometry with 50 μmx200 μm square hatches added across the rails with a pitch of 75 μm. 3) One 150 μm wide mating partner leaving 25 μm of open area at either side. For all geometries, the other mating partner is a continuous 200 μm wide seal-frame. A 46 % reduction in squeeze out could be seen in the bond with asymmetric bonding partners, but no significant reduction was measured for the geometry with rails and the geometry with hatches. The hatched, railed and asymmetric seal-frames displayed shear strengths of 57 ± 13 MPa, 80 ± 18 MPa, and 48 ± 30 MPa respectively, which was significantly higher than that of the traditional continuous bonds which only measured 17 ± 7 MPa. Fracture surface analysis showed no correlation between fracture modes and differences in shear strengths.