Application of Metallographic Microscopes in PCB Manufacturing
It plays a role in incoming inspection of raw materials. Copper-clad laminates required for the production of multi-layer PCBs directly determine the production quality of multi-layer PCBs. The following critical information can be obtained from sections observed under a metallographic microscope:
① Copper foil thickness: Verify whether the copper foil thickness meets the manufacturing requirements of multi-layer printed boards.
② Thickness of dielectric layers and the stacking arrangement of prepregs.
③ The warp and weft arrangement of glass fibers and resin content in the dielectric material.
④ Defect information of laminates observed by metallographic microscope. The main laminate defects are listed below:
(1) Pinholes: Small holes that completely penetrate one layer of metal. This type of defect is generally unacceptable for multi-layer printed boards with high wiring density.
(2) Pockmarks and dents: Pockmarks refer to tiny holes that do not fully penetrate the metal foil. Dents are gentle depressions formed on the copper foil surface after lamination, which are caused by local protrusions on the pressing steel plate during lamination. Measurements of hole size and dent depth on metallographic sections determine whether such defects are acceptable.
(3) Scratches: Fine shallow grooves scratched on the copper foil surface by sharp objects. Measurements of scratch width and depth on metallographic sections determine whether such defects are acceptable.
(4) Wrinkles: Folds or creases on the copper foil of the laminate. This defect is not permitted as observed on metallographic sections.
(5) Lamination voids, white spots and delamination blisters: Lamination voids are unfilled regions inside the laminate where resin and adhesive should be present. White spots are internal substrate defects where glass fibers separate from the resin at fabric weave intersections, appearing as scattered white spots or "cross patterns" beneath the substrate surface. Blisters are local separation caused by partial expansion between substrate layers or between the substrate and conductive copper foil. Acceptance of such defects is judged case by case.
