Toughened and Higher Fracture Crack-Resistant Polyimide
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-03
Crack propagation in polyimide (PI) films can be lessened by incorporating about 10-25% high molecular weight PI. A residual stress, due mainly to thermal expansion difference, of 5000-7000 psi is present on PI film on a substrate due to various process steps (such as, for example, via hole generation). There are always stress concentrations in the PI film which raise the stress to the point where the residual stress is the same as the yield strength of the material. Also, there will be some small cracks or crazes, either sharp or rounded, produced near the vias or at the point of the defects. The problem of rapid fracture crack propagation can be alleviated by incorporating a small (10-25%) fraction of a very high molecular weight PI of the same chemistry (or of different chemistry if miscible).