One of the inspections that we perform in our laboratory most frequently is the cross section analysis to evaluate the structural integrity. This is a destructive test in which we evaluate, among other parameters, the quality of vias , blind vias or burried vias.
For this analysis, we cut a coupon from a printed circuit board from your order and embed it in a transparent two-component resin. We then prepare the sample with wet sandpaper of different grains on a rotating grinding disc. The preparation ends in a polishing with a diamond-emulsion having a grain size of 1 micron. The crystalline structure of the different layers of copper, we can highlight with an additional preparation step that makes the structure of the metallization visible.
Under a light microscope with a digital camera system, we evaluate the cross section sample. The quantitative characteristics we document in your analysis report of a multilayer printed circuit board are typically:
- copper layer thickness of the metallization in the smallest hole (barrel thickness)
- copper layer thicknesses of the outer and inner layers
- dielectric layer thicknesses (prepreg and core layers)
- soldermask thickness on the conductor edge and on the base material
- total thickness of the finish surface (e.g. ENIG)
If you wish, we can also provide the track widths of structured inner layers in your report, which may be useful for example to check the requirements for controlled impedances.