Deformation Characteristics of Micron-level Thin Adhesive Layer for Bumpless Build Cube (BBCube) Integration Technology

In Bumpless Build Cube (BBCube) integration technology using Wafer-on-Wafer (WOW) and Chip-on-Wafer (COW) processes, the deformation characteristics when a micron-level thin adhesive layer was employed during the bonding process were studied for the first time. Three different types of compression tests were applied to a 2 μm-thick adhesive layer. The displacement under cyclical compression of < 5 N saturated at less than 1 μm. A stress decrease with elapsed time at constant displacement was observed in a stress relaxation test. When applying compressive stress with an elapsed time of 100 s, the thickness at the edge of the sample decreased 5% compared with that at the center of the sample. The adhesive layer deformed with time and exhibited viscoelastic deformation. This behavior can be examined for optimizing the bonding conditions for reducing nonuniformity of a thin adhesive layer in the stacking process since the thickness of the adhesive determines the aspect ratio of through-silicon-via (TSV) interconnects.