Effective thermal modelling evaluation and non-destructive tests for thermal via-structures in organic multi layer PCBs

This paper derives and evaluates an effective thermal material simulation model in simula-tion and experiment as well as proposes a non-destructive failure analysis for multi-layer sub-strates with thermal or electrical vias to derive exact failure data to supplement existing life-time models. The effective thermal material simulation model is investigated for a test matrix of repre-sentative structures. It results in a via structure class-dependent correction factor. As non-destructive failure test the pulse IR thermography using electrical and laser excita-tion was chosen as an analytic method to ob-serve and quantify crack growths in vias. The method shows that cracks are detectable un-ambiguously and its advantage over the ohmic test. The electrical excitation correlates well with the FE-simulation for different crack length in the cylindrical via structure. The laser excitation shows also a good agreement with the FE-simulation and has in contrast to the electrical excitation a good potential for large-scale screening as the board can be stepwise thermally excited and screened in one go with-out having any additional measuring lines. The results were validated with a 3D computer tomography analysis.