Hydrophobic silane coating for preventing conductive anodic filament (CAF) growth in printed circuit boards

A method of making a printed circuit board (PCB), comprising the steps of:

• providing a substrate that includes glass fiber;
• applying a silane coupling agent to the surface of the substrate, wherein the silane coupling agent includes an organofunctional group to bind to a varnish coating and a hydrolyzable group that binds to the surface of the substrate for coupling the substrate to the varnish coating, and wherein the surface of the substrate having the silane coupling agent applied thereto includes one or more surface silanols;
• applying a silane composition comprising a silane selected from a group consisting of chlorotrimethylsilane, hexamethyldisilazane, perfluorooctyl-1H,1H,2H,2H dimethylchlorosilane, (3,3,3-trifluoropropyl)dimethyl-chlorosilane, and combinations thereof, to the surface of the substrate having the silane coupling agent applied thereto to form a hydrophobic silane coating a monolayer thick that is an intermixed layer of the silane composition and the silane coupling agent, wherein the silane composition reacts with the one or more surface silanols, and wherein the hydrophobic silane coating presents a surface that is hydrophobic and essentially silanol-free;
• after the step of applying a silane composition, drying the surface presented by the hydrophobic silane coating;
• after the drying step, applying the varnish coating over the surface presented by the hydrophobic silane coating, wherein the silane coupling agent couples the varnish coating to the substrate;
• and
• subjecting the substrate, the hydrophobic silane coating and the varnish to curing conditions so as to define a PCB.