Hydrophobic Silane Coating for Preventing Conductive Anodic Filament (CAF) Growth in Printed Circuit Boards
An enhanced substrate for making a printed circuit board (PCB) includes a hydrophobic silane coating of a silane composition intermixed with a silane coupling agent applied to a glass fiber substrate. The silane coupling agent is applied to the surface of the substrate for coupling the substrate to a varnish coating. Applying the silane coupling agent to the surface of the substrate creates surface silanols, which are implicated in conductive anodic filament (CAF) growth. A silane composition, which reacts with the surface silanols, is applied to the surface of the substrate having the silane coupling agent applied thereto to form the hydrophobic silane coating. The surface presented by the hydrophobic silane coating/substrate is hydrophobic and essentially silanol-free. This surface is then dried, and varnish is applied thereto. Then, the substrate, hydrophobic silane coating and varnish are subjected to curing conditions to define the PCB.
1 . An enhanced substrate for a printed circuit board (PCB), comprising:
a substrate that includes glass fiber; and
a hydrophobic silane coating of a silane composition intermixed with a silane coupling agent applied to the substrate, wherein the hydrophobic silane coating/substrate presents a surface that is hydrophobic and essentially silanol-free.
2 . The enhanced substrate as recited in claim 1 , wherein the substrate comprises a sheet of woven glass fibers.
3 . The enhanced substrate as recited in claim 1 , wherein the hydrophobic silane coating is formed by applying a silane composition to the surface of the substrate having the silane coupling agent applied thereto, wherein the silane composition includes a silane having a general structure R 1 —S—R (2,3,4) , wherein R 1 is a functional group that is reactive with one or more surface silanols created when the silane coupling agent is applied to the surface of the substrate, and wherein R 2 , R 3 and R 4 are each a functional group that is hydrophobic and non-reactive with the one or more surface silanols.
4 . The enhanced substrate as recited in claim 1 , wherein the hydrophobic silane coating is formed by applying a silane composition to the surface of the substrate having the silane coupling agent applied thereto, and wherein the silane composition includes a silane selected from a group consisting of chlorotrimethylsilane, hexamethyldisilazane, perfluorooctyl-1H,1H,2H,2H-dimethylchlorosilane, and (3,3,3-trifluoropropyl)dimethyl-chlorosilane; and combinations thereof.
5 . The enhanced substrate as recited in claim 1 , wherein the hydrophobic silane coating is a monolayer thick.
6 . The enhanced substrate as recited in claim 1 , further comprising a varnish coating on the surface presented by the hydrophobic silane coating/substrate, wherein the silane coupling agent couples the varnish coating to the substrate.
7 . A printed circuit board (PCB) comprising at least one enhanced substrate according to claim 6 .
8 . A method of making an enhanced substrate for a printed circuit board, comprising the steps of:
providing a substrate that includes glass fiber;
applying a silane coupling agent to the surface of the substrate, wherein the surface of the substrate having the silane coupling agent applied thereto includes one or more surface silanols; and
applying a silane composition to the surface of the substrate having the silane coupling agent applied thereto to form a hydrophobic silane coating comprising 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/substrate presents a surface that is hydrophobic and essentially silanol-free.
9 . The method as recited in claim 8 , wherein the substrate comprises a sheet of woven glass fibers.
10 . The method as recited in claim 8 , wherein the silane composition includes a silane having a general structure R 1 —S—R (2,3,4) , wherein R 1 is a functional group that is reactive with alcohols, water and/or the one or more surface silanols, and wherein R 2 , R 3 and R 4 are each a functional group that is hydrophobic and non-reactive with the alcohols, water and/or the one or more surface silanols with which R 1 is reactive.
11 . The method as recited in claim 8 , wherein the silane composition includes a silane selected from a group consisting of chlorotrimethylsilane, hexamethyldisilazane, perfluorooctyl-1H,1H,2H,2H-dimethylchlorosilane, and (3,3,3-trifluoropropyl)dimethyl-chlorosilane; and combinations thereof.
12 . The method as recited in claim 8 , wherein the hydrophobic silane coating is a monolayer thick.
13 . The method as recited in claim 8 , wherein the step of applying the silane composition includes the steps of:
drying the surface of the substrate having the silane coupling agent applied thereto;
after the step of drying the surface of the substrate having the silane coupling agent applied thereto, placing the substrate having the silane coupling agent applied thereto in a vapor phase of the silane composition to form the hydrophobic silane coating by vapor deposition;
after the step of placing the substrate in a vapor phase of the silane composition, drying the surface presented by the hydrophobic silane coating/substrate.
14 . The method as recited in claim 8 , wherein the step of applying the silane composition includes the steps of:
placing the substrate having the silane coupling agent applied thereto in a solution of the silane composition and a hydrocarbon solvent;
after the step of placing the substrate having the silane coupling agent applied thereto in a solution of the silane composition in a hydrocarbon solvent, drying the surface presented by the hydrophobic silane coating/substrate.
15 . 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 surface of the substrate having the silane coupling agent applied thereto includes one or more surface silanols;
applying a silane composition to the surface of the substrate having the silane coupling agent applied thereto to form a hydrophobic silane coating comprising 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/substrate 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/substrate;
after the drying step, applying a varnish over the surface presented by the hydrophobic silane coating/substrate, 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.
16 . The method as recited in claim 15 , wherein the substrate comprises a sheet of woven glass fibers.
17 . The method as recited in claim 15 , wherein the silane composition includes a silane having a general structure R 1 —S—R (2-4) , wherein R 1 is a functional group that is reactive with alcohols, water and/or the one or more surface silanols, and wherein R 2 , R 3 and R 4 are each a functional group that is hydrophobic and non-reactive with the alcohols, water and/or the one or more surface silanols with which R 1 is reactive.
18 . The method as recited in claim 15 , wherein the silane composition includes a silane selected from a group consisting of chlorotrimethylsilane, hexamethyldisilazane, perfluorooctyl-1H,1H,2H,2H-dimethylchlorosilane, and (3,3,3-trifluoropropyl)dimethylchlorosilane; and combinations thereof.
19 . The method as recited in claim 15 , wherein the hydrophobic silane coating is a monolayer thick.
20 . The method as recited in claim 15 , wherein the step of applying the silane composition includes the steps of:
drying the surface of the substrate having the silane coupling agent applied thereto;
after the step of drying the surface of the substrate having the silane coupling agent applied thereto, placing the substrate having the silane coupling agent applied thereto in a vapor phase of the silane composition to form the hydrophobic silane coating by vapor deposition.
21 . The method as recited in claim 15 , wherein the step of applying the silane composition includes the steps of:
placing the substrate having the silane coupling agent applied thereto in a solution of the silane composition and a hydrocarbon solvent.