Non-cyanide electrode cleaning process

Abstract

An electrolytic process employing a water solution of metal lactates or lactic acid and metal hydroxides, rapidly and safely removes metal plating bleed, residual oxides or the like (stains), plastic flash, resin bleed and deflashing media, from electrodes of electronic devices. Anodic etching or a combination of cathodic and anodic etching is preferred. Noble metals are selectively removed without cyanide compounds. For example, excess silver from spot plating on copper leadframes is etched away 2-3 times faster than the underlying copper. After cleaning the device leads are bright, polished, stain-free and without scale, residual plating bleed, deflashing media, plastic flash or resin bleed. The process is effective, less hazardous, easy to use and economical.

We claim: 
     
       1. A method for cleaning leads of electronic devices comprising: providing leads of a first metal having thereon a plated region of a second metal, wherein the first metal comprises copper and the second metal comprises silver or other noble metal; and   immersing the leads in a solution comprising lactic acid and a metal hydroxide and applying an electrical potential between the leads and a reference electrode contacting the solution to remove silver or other noble metal at a rate faster than the removal rate of copper.   
     
     
       2. The method of claim 1 wherein the immersing step comprises immersing in a solution comprising lactic acid and a hydroxide of a metal from columns 1A or 2A of the periodic table. 
     
     
       3. The method of claim 2 wherein the immersing step comprises immersing in a solution comprising lactic acid and potassium or sodium hydroxide or a combination thereof. 
     
     
       4. The method of claim 1 wherein the applying step comprises making the leads anodic with respect to the reference electrode for a predetermined first time. 
     
     
       5. The method of claim 1 wherein the immersing step comprises immersing in a solution having proportions comprising about 10-30% by volume of about 60% concentration potassium or sodium lactate or a combination thereof in water. 
     
     
       6. The method of claim 1 wherein the immersing step comprises immersing in a solution having proportions comprising about 10 to 30 liters of lactic acid and about 5 to 30 Kgms of KOH or NaOH or a combination thereof in water per 100 liters of solution. 
     
     
       7. The method of claim 1 wherein the immersing step comprises immersing in a solution having proportions comprising about 10 to 30 liters of lactic acid and about 5 to 30 Kgms of KOH, NaOH or a mixture thereof in water, or an equivalent solution of potassium or sodium lactate in water, together with sufficient other inorganic acid to give a pH in the range of 1.4-2, per 100 liters of solution. 
     
     
       8. The method of claim 1 wherein the immersing step comprises immersing in the solution for a cleaning time in the range of about 2-200 seconds. 
     
     
       9. The method of claim 8 wherein the immersing step comprises immersing in the solution for a cleaning time in the range of about 10-40 seconds. 
     
     
       10. The method of claim 1 wherein the immersing step comprises immersing in a solution having a pH in the range of 1.4-7. 
     
     
       11. A method for cleaning leads of electronic devices comprising, providing leads of a first metal having .Iadd.thereon .Iaddend.a plated region of a second metal, immersing the leads in a solution comprising lactic acid and a metal hydroxide, and applying an electrical potential between the leads and a reference electrode contacting the solution, wherein the applying step comprises first making the leads cathodic with respect to the reference electrode for a predetermined first time and then making the leads anodic with respect to the reference electrode for a predetermined second time. 
     
     
       12. A method for cleaning leads of electronic devices comprising, providing leads of a first metal having thereon a plated region of a second metal, immersing the leads in a solution comprising lactic acid and a metal hydroxide, and applying an electrical potential between the leads and a reference electrode contacting the solution, wherein the immersing step comprises first immersing in a first solution having proportions comprising about 3-6 Kgms KOH, NaOH or mixture thereof in water per 100 liters of the first solution and applying cathodic potential to the leads, and then immersing the leads in a second solution having proportions comprising about 10 to 30 liters of lactic acid and about 5 to 30 Kgms of KOH or NaOH or a combination thereof in water per 100 liters of the second solution or an equivalent solution of potassium or sodium lactate in water and applying anodic potential to the leads. 
     
     
       13. A method for cleaning leads of electronic devices comprising, providing leads of a first metal having thereon a plated region of a second metal, immersing the leads in a solution comprising lactic acid and a metal hydroxide, and applying an electrical potential between the leads and a reference electrode contacting the solution, wherein the applying step comprises applying a cathodic and anodic voltage to the leads wherein the relative cathodic and anodic time durations are in proportion of about 1:1 to 1:2, respectively. 
     
     
       14. A method for treating parts of a first metal having thereon an exposed region of a second metal to remove the exposed second metal, comprising, immersing the metal parts in a solution comprising lactic acid and a metal hydroxide and a polar solvent, and applying an electrical potential between the metal parts and a reference electrode contacting the solution, wherein the first metal comprises copper and the second metal comprises silver .[.of.]. .Iadd.or .Iaddend.another noble metal. 
     
     
       15. The method of claim 14 wherein the applying step comprises applying anodic potential to the metal parts. 
     
     
       16. A method for treating metal parts of a first metal having thereon an exposed region of a second metal, to remove at least part of the exposed second metal, comprising, immersing the metal .[.pear.]. .Iadd.parts .Iaddend.in a solution comprising lactic acid and a metal hydroxide and a polar solvent, and applying an electrical potential between the metal parts and a reference electrode contacting the solution, wherein the first metal comprises copper and the second metal comprises a noble metal, and wherein the applying step comprises first applying cathodic potential .Iadd.and then applying anodic potential .Iaddend.to the metal parts. 
     
     
       17. A method for treating metal parts of a first metal having thereon an exposed region of a second metal, to remove at least part of the exposed second metal, comprising, immersing the metal parts in a solution comprising lactic acid and a metal hydroxide and a polar solvent, and applying an electrical potential between the metal parts and a reference electrode contacting the solution, wherein the first metal comprises copper and the second metal comprises a noble metal, and further, prior to the immersing and applying steps, placing the parts in another solution comprising a metal hydroxide and a polar solvent wherein the parts are subjected to a cathodic potential, and then performing the immersing and applying steps wherein anodic potential is applied to the parts. 
     
     
       18. A method for cleaning copper leads that have exposed silver thereon comprising: immersing the leads in a cleaning solution comprising a polar solvent in which has been dissolved lactic acid and a metal hydroxide, or a metal lactate; and   applying an anodic potential to the leads .[.to.]. to remove silver more rapidly than copper.   
     
     
       19. A method for cleaning copper leads that have exposed silver thereon comprising, immersing the leads in a .[.clean.]. .Iadd.cleaning .Iaddend.solution comprising a polar solvent in which has been dissolved lactic acid and a metal hydroxide, or a metal lactate, and applying an anodic potential to the leads, and further comprising prior to the immersing and applying steps, placing the leads in another solution comprising a metal hydroxide .[.a.]. .Iadd.and .Iaddend.a polar solvent wherein the leads are subjected to a cathodic potential. .Iadd.20. A method of removing non-metal material from metal surfaces comprising the steps of: providing a metal surface having thereon non-metal material to be removed; and   immersing said metal surface in a solution comprising lactic acid and a metal hydroxide and applying an electrical potential between said metal surface and a reference electrode contacting said solution to remove said non-metal material at a rate faster than the removal rate of the metal. .Iaddend. .Iadd.21. The method of claim 20 wherein the immersing step comprises immersing in a solution comprising lactic acid and a hydroxide of a metal from column 1A or 2A of the periodic table. .Iaddend. .Iadd.22. The method of claim 21 wherein the immersing step comprises immersing in a solution of lactic acid and potassium or sodium hydroxide or a combination thereof. .Iaddend. .Iadd.23. The method of claim 20 wherein the metal surface is made anodic with respect to the reference electrode for a   
     
     
        predetermined first time. .Iaddend. .Iadd.24.  The method of claim 20 wherein the immersing step comprises immersing in a solution having proportions comprising about 10 to 30% by volume of about 60% concentration potassium or sodium lactate or a combination thereof in water. .Iaddend. .Iadd.25. The method of claim 20 wherein the immersing step comprises immersing in a solution having proportions comprising about 10 to 30 liters of lactic acid and about 5 to 30 Kgms of KOH, NaOH or a combination thereof in water per 100 liters of solution. .Iaddend. .Iadd.26. The method of claim 20 wherein the immersing step comprises immersing in a solution having proportions comprising about 10 to 30 liters of lactic acid and about 5 to 30 Kgms of KOH, NaOH or a combination thereof in water, or an equivalent solution of potassium or sodium lactate in water, together with sufficient other inorganic acid to give a pH in the range 1.4 to 2, per 100 liters of solution. .Iaddend. .Iadd.27. The method of claim 20 wherein the immersing step comprises immersing in the solution for a time in the range of about 2 to 200 seconds. .Iaddend. .Iadd.28. The method of claim 27 wherein the immersing step comprises immersing in the solution for a time in the range of about 10 to 40 seconds. .Iaddend. .Iadd.29. The method of claim 20 wherein the immersing step comprises immersing in a solution having a pH in the range of 1.4 to 7. .Iaddend. .Iadd.30. The method of claim 20 wherein the providing step comprises providing a copper surface having one or more of oxide, plastic, 
     
     
        resin or deflashing media to be removed. .Iaddend. .Iadd.31.  The method of claim 30 wherein the providing step comprises providing copper leads of electronic devices. .Iaddend. .Iadd.32. A method for removing non-metal materials from copper comprising: immersing copper having non-metal material thereon in a solution comprising a polar solvent in which has been dissolved lactic acid and a metal hydroxide or a metal lactate; and   applying an anodic potential to said copper to remove said non-metal material more rapidly than said copper. .Iaddend. .Iadd.33. The method of claim 32 wherein the applying step includes removing one or more of oxide, plastic, resin and deflashing media. .Iaddend. .Iadd.34. A method for cleaning copper having non-metal material thereon comprising immersing said copper in a solution comprising a polar solvent in which has been dissolved lactic acid and a metal hydroxide or a metal lactate, and applying an anodic potential to said copper and further comprising prior to the immersing and applying steps, placing said copper in another solution comprising a metal hydroxide and polar solvent wherein said copper is subjected to a cathodic potential. .Iaddend. .Iadd.35. The method of claim 34 wherein the non-metal material includes one or more of oxide, plastic, resin or deflashing media. .Iaddend. .Iadd.36. A method for cleaning leads of electronic devices comprising providing metal leads having non-metal material thereon, immersing said leads in a solution comprising lactic acid and a metal hydroxide and applying an electrical potential between said leads and a reference electrode contacting said solution, wherein the immersing step comprises first immersing in a first solution having proportions comprising about 3 to 6 Kgms KOH, NaOH, or a mixture thereof in water per 100 liters of said first solution and applying cathodic potential to said leads, and then immersing said leads in a second solution having proportions comprising about 10 to 30 liters of lactic acid and about 5 to 30 Kgms of KOH, NaOH or a combination thereof in water per 100 liters of said second solution or an equivalent solution of potassium or sodium lactate in water and applying an anodic potential to said leads. .Iaddend. .Iadd.37. A method for removing non-metal material from metal surfaces comprising providing a metal surface having thereon non-metal material to be removed, immersing said metal surface in a solution comprising lactic acid and a metal hydroxide and applying an electrical potential between said metal surface and a reference electrode contacting said solution wherein the applying step comprises a applying cathodic and anodic voltage to said metal surface wherein the relative cathodic and anodic time durations are in proportion of about 1:1 to 1:2 respectively. .Iaddend. .Iadd.38. The method of claim 37 wherein the metal comprises copper and the non-metal material is one or more of oxide, plastic, resin and deflashing media. .Iaddend. .Iadd.39. The method of claim 38 wherein the metal comprises leads of electronic devices. .Iaddend. .Iadd.40. An electrolytic bath for differentially removing noble metals and non-metal material from copper consisting essentially of lactic acid and a metal hydroxide in aqueous solution.   
     
     
        .Iaddend. .Iadd.41.  The bath of claim 40 wherein the metal hydroxide is a hydroxide of a metal from columns 1A or 2A of the periodic table. .Iaddend. .Iadd.42. The bath of claim 41 wherein the metal hydroxide comprises potassium or sodium hydroxide or a combination thereof. .Iaddend. .Iadd.43. The bath of claim 40 wherein the solution has proportions comprising about 10 to 30% by volume of about 60% concentration potassium or sodium lactate or a combination thereof in water. .Iaddend. .Iadd.44. The bath of claim 40 wherein the solution has proportions comprising about 10 to 30 liters of lactic acid and about 5 to 30 Kgms of KOH or NaOH or a combination thereof in water per 100 liters of solution. .Iaddend. .Iadd.45. The bath of claim 40 having a pH of 1.4 to 7. .Iaddend. .Iadd.46. The bath of claim 40 wherein said bath differentially removes one or more of silver, oxide, plastic, resin or 
     
     
        deflashing media from copper. .Iaddend. .Iadd.47.  An electrolytic bath for differentially removing noble metals and non-metal materials from copper wherein the solution has proportions comprising about 10 to 30 liters of lactic acid and about 5 to 30 Kgms of KOH, NaOH or a combination thereof in water or an equivalent solution of potassium or sodium lactate in water, together with sufficient other inorganic acid to give a pH in the range of 1.4 to 2, per 100 liters of solution.