Fine Cone-shaped Bumps for Three-dimensional LSI Package—An Optimization of Thermocompression Bonding Process

Fine cone-shaped bumps (6 µm) were fabricated by a nanoparticle deposition method, where the nanoparticles were deposited onto hole patterns defined in a photoresist.In this work, the goal is to minimize the flip-chip bonding force of LSI chips targeted for three-dimensional (3D) packages while optimizing the bonding strength.In particular, the effects of temperature on the bump compressive stress and shear strength were investigated in detail.From the results, it was found that the crystal grain size of cone-shaped gold bumps increases significantly at ≥150 ℃, which in turn affects the mechanical properties of the bump.We also clarified the optimum connection conditions to simultaneously realize a low bonding force and an improved bonding strength by bonding at ≥200 °C.