Reliability and fracture of metal-polymer structures with fine-line geometries [packaging]

The fracture behavior of metal-polymer line structures as a function of dimensions was investigated using a stretch-deformation technique. The effects of line orientation, line width, and film thickness are reported. When the line orientation is parallel to the stretching direction, only formation of cracks normal to the lines is observed. However, when the line is perpendicular to the stretching direction, delamination becomes the dominant mode of fracture. Wide lines (16 μm) exhibit larger shear stress at the edge of the metal-polymer interface, therefore delaminating earlier than narrow lines (4 μm). By decreasing the metal film thickness, the depth of stress penetration at the interface decreases, making the propagation of cracks more difficult in thin films than in thick films. Finite-element analysis has been carried out to account for the experimental observations, and good agreement was obtained. In the analysis, the plastic deformation characteristics of the metal and the polymer have been specifically taken into account. In comparison with a linear elastic analysis, the linear model predicts significantly higher stress levels and local concentrations than the nonlinear model