Green Epoxy

Several epoxy resin systems are green in color. This started with fiberglass finishes that had chromium chemistry as their base with the trade name of Volan, which produced a green finish. Now, very few manufacturers use Volan, and use organosilanes instead. However, the complaints from end users about the change in appearance of their product have forced the suppliers to start dying their FR-4 products green to make them look same as before. That explains the reason for green being so common a color for epoxy printed circuit boards.

Smooth resin rich surfaces offer a better fill for internal etched copper patterns. This is often a result of lightweight fabrics with high resin content. Using heavier fabrics result in lower cost, while offering enhanced dimensional stability and permit building up greater thickness at lower cost per mil. However, the use of heavier fabrics usually affects drilling characteristics and surface smoothness. Although thicker and heavier fabrics result in low-cost rigid laminates, they can deflect small drill bits causing them to break.

Warp, Fill, and Direction of Weave

For a woven fabric, the term warp indicates the direction of the length of the roll, while fill indicates the direction of the yarns that fill in from side to side in the weaving process. In commonly used fabrics, the tensions and the number of yarns are not evenly balanced and that has a varying effect on stability and subsequently on registration. For a PCB fabricator, it is necessary to know the direction of warp and fill so they can orient them similarly each time and adjust the processing and compensate for predictable effects.

For instance, for a laminate measuring 36 x 48 inches, the warp is normally parallel to the longer dimension. Unless the customer makes a special request, or it is necessary to cut otherwise, the warp usually follows the longest dimension of a piece of cut panelized or prepreg laminate. When warp is not along the longest dimension, or for square panels, the fabricator marks the warp direction clearly by an arrow on the package or on the material.