Chip-on-Board (CoB) technology for low temperature environments. Part I: Wire profile modeling in unencapsulated chips

An analytical model based on elastic strain energy minimization is developed for estimating the wire profile in unencapsulated ball-wedge wire bond configuration for chip-on-board (CoB) technology. The wire profile is applicable to ball-wedge bonds with a height offset, and is modeled using a piece-wise continuous polynomial function (cubic spline) with appropriate boundary conditions at the two bond sites. Plastic deformation is ignored in the current analysis as a first-order approximation, since the interest is in parametric sensitivity studies. The model is useful for estimating the wire profile for different offset heights and wire spans, and serves as a starting point for subsequent thermomechanical stress analysis after encapsulation. Parametric studies are presented to explore the wire profile for different CoB geometries.