Methods of treating copper surfaces for enhancing adhesion to organic substrates for use in printed circuit boards
Embodiments of the present invention relates generally to the manufacture of printed circuit boards (PCB's) or printed wiring boards (PWB's), and particularly to methods for treating smooth copper surfaces to increase the adhesion between a copper surface and an organic substrate. More particularly, embodiments of the present invention related to methods of achieving improved bonding strength of PCBs without roughening the topography of the copper surface. The bonding interface between the treated copper and the resin layer of the PCB exhibits excellent resistance to heat, moisture, and chemicals involved in post-lamination process steps.
1. A method of fabricating a printed circuit board having at least an organic substrate and a copper surface, comprising the steps of:
cleaning the copper surface with an alkaline and/or peroxide solution;
stabilizing the copper surface by forming a copper oxide layer on the copper surface by exposing the copper surface to an oxidant and coupling one or more molecules to the copper oxide layer, the one or more molecules comprising a thermally stable base bearing one or more binding groups configured to bind the copper oxide layer and one or more attachment groups configured to attach to the organic substrate;
terminating formation of the copper oxide by a self-limiting reaction between the copper oxide and the one or more molecules;
conditioning the stabilized copper surface by reducing the copper oxide layer with a reducing agent; and
bonding the stabilized copper surface with a resin.
2. The method of claim 1 , wherein the stabilizing step is carried out at a temperature of 50-80° C.
3. The method of claim 1 wherein the copper oxide layer after conditioning has a thickness of about 200 nanometers or less.
4. The method of claim 1 wherein the copper oxide layer after conditioning is comprised of a substantially amorphous structure.
5. The method of claim 1 wherein the copper oxide layer has grains, and after conditioning the grains have a size of 250 nanometers or less.
6. The method of claim 1 wherein the copper oxide layer has grains, and after conditioning the grains have a size of 200 nanometers or less.
7. The method of claim 1 wherein the copper oxide has grains, and after conditioning the grains are randomly oriented.
8. The method of claim 1 wherein the oxidant is selected from the group consisting of sodium chloride, sodium hydroxide, hydrogen peroxide, permanganate, perchlorate, persulfate, ozone, and mixtures thereof.
9. The method of claim 1 wherein the reducing agent is selected from the group consisting of formaldehyde, sodium thiosulfate, sodium borohydride, a borane reducing agent represented by the general formula BH 3 NHRR′, wherein R and R′ are each selected from the group consisting of H, CH 3 and CH 2 CH 3 , dimethylamine borane (DMAB), a cyclic borane, morpholine borane, pyridium borane, and piperidine borane.
10. The method of claim 1 wherein the method is carried out for a time in the range of about 2 to 20 minutes.
11. The method of claim 1 wherein the one or more molecules is selected from the group consisting of a porphyrin, a porphyrinic macrocycle, an expanded porphyrin, a contracted porphyrin, a linear porphyrin polymer, a porphyrinic sandwich coordination complex, and a porphyrin array.
12. The method of claim 1 , wherein the one or more molecules comprises a surface active moiety.
13. The method of claim 12 wherein said surface active moiety is selected from the group consisting of a macrocyclic proligand, a macrocyclic complex, a sandwich coordination complex and polymers thereof.
14. The method of claim 12 wherein said surface active moiety is a porphyrin.
15. The method of claim 1 wherein the one or more attachment groups is comprised of an aryl functional group and/or an alkyl attachment group.
16. The method of claim 15 wherein the aryl functional group comprises a functional group selected from the group consisting of acetate, alkylamino, allyl, amine, amino, bromo, bromomethyl, carbonyl, carboxylate, carboxylic acid, dihydroxyphosphoryl, epoxide, ester, ether, ethynyl, formyl, hydroxy, hydroxymethyl, iodo, mercapto, mercaptomethyl, Se-acetylseleno, Se-acetylselenomethyl, S-acetylthio, S-acetylthiomethyl, selenyl, 4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl, 2-(trimethylsilyl)ethynyl, vinyl, and combinations thereof.
17. The method of claim 15 wherein the alkyl attachment group comprises a functional group selected from the group consisting of acetate, alkylamino, allyl, amine, amino, bromo, bromomethyl, carbonyl, carboxylate, carboxylic acid, dihydroxyphosphoryl, epoxide, ester, ether, ethynyl, formyl, hydroxy, hydroxymethyl, iodo, mercapto, mercaptomethyl, Se-acetylseleno, Se-acetylselenomethyl, S-acetylthio, S-acetylthiomethyl, selenyl, 4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl, 2-(trimethylsilyl)ethynyl, vinyl, and combinations thereof.
18. The method of claim 1 wherein the one or more attachment groups comprises an alcohol or a phosphonate.
19. The method of claim 1 wherein the one or more attachment groups is selected from the group consisting of amines, alcohols, ethers, other nucleophiles, phenyl ethynes, phenyl allylic groups, phosphonates and combinations thereof.
20. The method of claim 1 wherein the one or more molecules is selected from the group consisting of a porphyrin, a porphyrinic macrocycle, an expanded porphyrin, a contracted porphyrin, a linear porphyrin polymer, a porphyrinic sandwich coordination complex, a porphyrin array, a silane, a tetraorgano-silane, aminoethyl-aminopropyl-trimethoxysilane, (3-Aminopropyl)trimethoxysilane, (1-[3-(Trimethoxysilyl)propyl]urea),(3-Aminopropyl) triethoxysilane, ((3-Glycidyloxypropyl)trimethoxysilane), (3-Chloropropyl) trimethoxysilane, (3-Glycidyloxypropyl)trimethoxysilane, Dimethyldichlorosilane, 3-(Trimethoxysilyl)propyl methacrylate, Ethyltriacetoxysilane, Triethoxy(isobutyl)silane, Triethoxy(octyl)silane, Tris(2-methoxyethoxy)(vinyl)silane, Chlorotrimethylsilane, Methyltrichlorosilane, Silicon tetrachloride, Tetraethoxysilane, Phenyltrimethoxysilane, Chlorotriethoxysilane, ethylene-trimethoxysilane, an amine, a sugar, and any combination thereof.
21. The method of claim 1 wherein the one or more molecules is selected from the group consisting of molybdates, tungstates, tantalates, niobates, vanadates, isopoly or heteropoly acids of molybdenum, tungsten, tantalum, niobium, vanadium, and any combination thereof.