Influence of wirebond shape on its lifetime with application to frame connections

The subject of this study was to investigate the effect of different geometrical loop shapes on the reliability of 400 μm thick Al bond wires in IGBT modules by means of experimental and analytical methods. The experimental fatigue tests have been realized by linear cyclic displacements of 5-45 μm of the contact plates at 200 Hz and 20 kHz. Life time curves were obtained for bond wire connections with different loop heights, distances and angles with the main failure mechanism being wire bond heel cracking. Furthermore an analytical model was developed to calculate the effect of variation of geometrical shape parameters on the stress at different locations of the bond wire. This model can be used to make a preliminary geometry selection of the bond wire and to predict the force or stress at critical sites of the wire bond during stress tests. This model was validated with finite element analysis.