FEM analysis of ball- and wedge bond techniques for the interconnection formation of soft die bonds

The paper describes three-dimensional, dynamic finite element simulations of wire bonding processes on silicon dies, which are bonded on soft interposers by soft adhesives. The application of soft materials below a die has increased e.g. due to a reduced influence of the substrate stiffness on a sensor chip. However, a soft die bond may cause trouble during the subsequent wire bonding process, because the soft interconnection may partially absorb the ultrasonic energy required for the welding of bond wire and pad metallization. Dynamic 3-D FEM simulations were done in order to assess the effect of different die adhesive stiffness on the resulting mechanical conditions during ultrasonic wedge bond and thermo-sonic ball bond processes. The study compares the effect of the die adhesives on the wire bond formation and stresses occurring in the die. Contact forces are also evaluated in order to estimate the induced ultrasonic energy, which is essential for the contact formation.