Method of generating precious metal-reducing patterns

Abstract

A pattern capable of reducing thereon a precious metal is generated on a suitable substrate by first coating selected portions of the substrate with a solution, called a photopromoter, which contains a metal salt. The metal salt possesses two characteristics: (a) the oxidation state of the salt (i.e., of the metal ion) is alterable (either increasable or decreasable) by exposure of the salt to radiation of the proper wavelength; and (b) in either the original or the altered oxidation state (but not in both states) the salt is capable of reducing a precious metal, e.g., a metal of the platinum group such as palladium, platinum or rhodium, from a salt thereof. The photopromoter-coated substrate is next selectively exposed to the proper wavelength radiation to produce a pattern of the photopromoter salt capable of reducing the precious metal. The remainder of the salt is incapable of reducing the precious metal. The pattern may then be exposed to a solution containing a salt of the precious metal to reduce thereon the precious metal. Ultimately, the precious metal pattern may be used to reduce electrolessly a metal, such as copper, to produce a metallic pattern, such as an electric circuit pattern.

What is claimed is: 
     
       1. A method of rendering an article selectively capable of reducing thereon a precious metal from a precious metal salt which method comprises the steps of: coating said article with a solution containing a salt of a metal selected from the group consisting of tin, titanium and lead, the oxidation state of the metal ion thereof being alterable by exposure to short wavelength ultraviolet light; and then   producing a pattern capable of reducing said precious metal from said precious metal salt by selectively exposing portions of said coated article to short wavelength ultraviolet light.   
     
     
       2. The method of claim 1 wherein said metal ion is capable of reducing said precious metal. 
     
     
       3. The method of claim 2 wherein said metal salt in said solution is a halide. 
     
     
       4. The method according to claim 3 wherein said halide in said solution is selected from the group consisting of tin chloride, titanium chloride and lead chloride. 
     
     
       5. The method according to claim 4 wherein said ultraviolet light has a wavelength of less than 3000 A. 
     
     
       6. The method according to claim 5 wherein said ultraviolet light has a wavelength within the approximate range of about 1800 A. to about 2700 A. 
     
     
       7. The method of claim 6 wherein exposing selectively said coated article portions to said short wavelength ultraviolet light renders said metal ion at said coated article portions incapable of reducing said precious metal. 
     
     
       8. The method of claim 7 wherein about 75% of said short wavelength ultraviolet light is at approximately the 2537 A. line and said exposure is continued until said coated article portions receive energy amounting to about 30 milliwatt-seconds/cm. 2  to about 1000 milliwatt-seconds/cm. 2 . 
     
     
       9. The method of claim 8 wherein said precious metal salts are selected from the group consisting of iridium, osmium, palladium, platinum, rhodium, ruthenium, gold and silver.  .[.10. A method of producing a metallic pattern on a substrate comprising the steps of: coating the substrate with a first solution containing a metal salt selected from the group consisting of ferric oxalate, ferric citrate, ferric tartrate mercuric oxalate mercuric citrate and mercuric tartrate, the oxidation state of the metal ion thereof being alterable by exposure to short wavelength ultraviolet light;   producing a pattern capable of reducing a precious metal from a precious metal salt by selectively exposing portions of said coated substrate to short wavelength ultraviolet light;   immersing the substrate in a precious metal salt solution to reduce on said pattern said precious metal; and then   placing said precious metal pattern in an electroless plating bath which is catalyzed by said reduced precious metal to produce the metallic pattern..]. .[.11. The method according to claim 10 wherein said ultraviolet light has a wavelength of less than 3000 A..]. .[.12. The method according to claim 11 wherein said ultraviolet light has a wavelength within the approximate range of about 1800 A. to about 2700 A..]. .[.13. The method of claim 12 wherein exposing selectively said coated substrate to said short wavelength ultraviolet light renders said metal ion capable of reducing said precious metal..]. .[.14. The method of claim 13 wherein about 75% of said short wavelength ultraviolet light is at approximately the 2537 A. line and said exposure is continued until said coated substrate receives energy amounting to approximately 25 milliwatt-seconds/cm. 2 ..]. .[.15. The method of claim 14 wherein said precious metal salts are salts of metals selected from the group consisting of iridium, osmium, palladium, platinum, rhodium, ruthenium, gold and silver..]. .[.16. The method of claim 15 wherein said coating and immersing steps are effected simultaneously by admixing said precious   
     
     
        metal salts and said metal salts in said first solution..]. 17. A method of producing a precious metal pattern on a substrate, the pattern being usable to catalyze and reduce thereon metal from an electroless bath, which method comprises: effecting the retention on selected areas of said substrate of a first solution containing a salt of a metal selected from the group consisting of tin, titanium and lead, the oxidation number of the metal ion of said first solution being alterable by exposure thereof to radiation deep within the ultraviolet spectrum;   selectively exposing said selected areas to said radiation to generate a pattern of said metal ion capable of reducing said precious metal; and then   immersing said pattern in a second solution containing a salt of said   
     
     
        precious metal to produce said precious metal pattern. 18. The method of 
     
     
        claim 17 wherein said salt is a metal halide. 19. The method of claim 18 wherein said metal halide is selected from the group consisting of tin 
     
     
        chloride, lead chloride and titanium chloride. 20. The method of claim 19 wherein said retention of said first solution is primarily by adsorption. 
     
     
         1. The method of claim 20 wherein said radiation is within the range of about 1800 A. to about 2700 A., with approximately 75% of said radiation 
     
     
        being at about the 2537 A. line. 22. The method of claim 21 wherein said selective exposure continues until said substrate areas receive energy therefrom in the approximate range of about 30 milliwatt-seconds/cm. 2  to about 1000 milliwatt-seconds/cm. 2 , the amount of said energy being approximately inversely proportional to the degree to which said first 
     
     
        solution is adsorbed on said substrate. 23. A method of producing a metallic pattern on a nonconductive substrate comprising the steps of: adsorbing onto selected surfaces of said substrate a metal halide solution, the metal being selected from the group consisting of tin, lead and titanium, the metal ion thereof being capable of reducing a precious metal from a precious metal salt;   exposing selected portions of said selected surfaces to ultraviolet light until said metal ion thereat is rendered incapable of reducing said precious metal from said precious metal salt, said selected portions conforming to a negative of said pattern and said ultraviolet light having a wavelength in the range of about 1800 A. to about 2700 A.;   immersing said substrate in said precious metal salt solution whereby said ion reduces said precious metal therefrom onto said surfaces in said pattern; and then   immersing said substrate in an electroless plating bath which is catalyzed   
     
     
        by said reduced precious metal to produce said metallic pattern. 24. The method of claim 23 which further includes an initial step of: forming 
     
     
        holes through said substrate outside of said selected portions. 25. The method of claim 24 wherein said precious metal salt is a salt of a metal selected from the group consisting of iridium, osmium, palladium, 
     
     
        platinum, rhodium, ruthenium, gold and silver. 26. A method of increasing the bond strength between a substrate and a metal pattern produced thereon by the method of claim 23 which comprises the steps of: selecting a substrate having a predetermined service temperature and which is permeable to an atmosphere conducive to the formation of an oxide of said metal;   depositing said metal pattern on said substrate, said metal being oxidizable in said atmosphere at a second temperature less than said service temperature;   placing said substrate with said pattern thereon in said atmosphere; and then   heating said pattern to said second temperature to form said oxide at the   
     
     
        substrate-pattern interface until said bond strength is increased. 27. A method of increasing the bond strength between a metallic pattern electrolessly deposited on a polyimide substrate and the substrate by the method of claim 23, the substrate having a predetermined service temperature, which method comprises: placing said substrate with said metal pattern thereon in an atmosphere conductive to the formation of an oxide of said metal, and then   heating said metal pattern to a temperature less than said service temperature and sufficient to oxidize said metal until sufficient oxide formation takes place at the substrate-pattern interface to increase said   
     
     
        bond strength. 28. A method of producing a metallic pattern on a substrate surface comprising the steps of: a. selecting a suitable substrate;   b. immersing a surface of said substrate in a metal halide solution, said metal being selected from the group consisting of lead, tin and titanium, said metal halide solution having a molar concentration in the approximate range of about .045 to about .3, said solution being retained on said substrate surface;   c. exposing selectively said surface to ultraviolet light in a negative of said pattern, said light having approximately 75% of its radiation at about the 2537 A. line, said radiation supplying energy to said surface within the approximate range of from about 30 milliwatt-seconds/cm. 2  to about 1000 milliwatt-seconds/cm. 2 .   d. immersing said exposed surface in a solution containing a salt of a precious metal selected from the group consisting of iridium, osmium, palladium, platinum, rhodium, ruthenium, gold and silver to reduce said metal in a positive of said pattern; and then   e. immersing said surface in an electroless plating bath to electrolessly   
     
     
        plate said precious metal positive to produce said metallic pattern. 29. The method of claim 28 in which step (a) further includes: selecting a substrate so that the retention of said solution on said substrate surface 
     
     
        in step (b) is effected primarily by adsorption. 30. The method of claim 29 wherein in step (c) the amount of said energy is inversely proportional to the degree to which said solution is adsorbed on said substrate 
     
     
        surface. 31. The method of claim 28 wherein step (b) further comprises: maintaining said metal halide solution at a pH within the approximate 
     
     
        range of from about .8 to about 3.5 during said immersion. 32. The method of claim 31 wherein step (a) further comprises: selecting a substrate at 
     
     
        least said surface of which is a polyimide. 33. The method of claim 32 wherein step (a) further comprises: cleaning said polyimide surface in 
     
     
        NaOH, and then rinsing said polyimide surface in clean water. 34. The method of claim 33 wherein step (b) further comprises, after said immersion: rinsing said substrate surface in clean water, and then drying 
     
     
        said substrate surface. 35. The method of claim 28 wherein step (a) further comprises: rendering said substrate surface nascent so that said solution in which said surface is immersed to adsorptively retained 
     
     
        thereon. 36. A method of producing an electrical circuit pattern on a non-conductive substrate which comprises the steps of: selecting a metal salt selected from the group consisting of tin halides, titanium halides, lead halides.[., ferric oxalate, ferric citrate, ferric tartrate, mercuric oxalate, mercuric citrate and mercuric tartrate.].;   coating said substrate with a solution containing said metal salt;   drying said coated substrate;   selectively exposing said dried substrate to radiation deep within the ultraviolet spectrum to generate a first pattern and a second pattern, said radiation being within the approximate range of 1800 A. to 2700 A. with approximately 75% of said radiation being at about the 2537 A. line, said radiation continuing until energy within the approximate range of 25 to 1000 milliwatt-seconds/cm. 2  has impinged on said dried substrate, said first pattern being capable of reducing a precious metal from a salt solution thereof, said second pattern being incapable of reducing a precious metal;   selecting a precious metal salt from the group of precious metals consisting of iridium, osmium, palladium, platinum, rhodium, ruthenium, gold and silver, said precious metal being catalytic to an electroless plating bath;   immersing said exposed substrate in a solution containing said precious metal salt, said first pattern reducing said precious metal thereon to generate a precious metal pattern; and then   immersing said precious metal pattern in an electroless plating bath to   
     
     
        produce said electric circuit pattern. 37. The method of claim 36 which comprises the additional step of: electroplating metal onto said 
     
     
        electrical circuit pattern. 38. The method of claim 37 which comprises the additional step of: removing said substrate from said electroplated circuit pattern.