Claims
- 1. A method of electrolessly gold plating copper portions on a substrate, said method comprising the steps of:
(1) cleaning said substrate, said cleaning including immersing said substrate in a cleaning solution and applying ultrasonic agitation to said cleaning solution during said immersion; (2) activating said copper portions; (3) depositing a layer of palladium on said copper portions; (4) electrolessly plating said copper portions with nickel; (5) electrolessly plating said copper portions with a first layer of gold; and (6) autocatalytically plating said copper portions with a second layer of gold.
- 2. The method of claim 1 wherein said substrate is a printed circuit board (PCB).
- 3. The method of claim 2 wherein step (2) comprises the steps of:
(2.1) immersing said PCB in a first solution comprising sulfuric acid and applying ultrasonic agitation to said first solution during said immersion; (2.2) rinsing said PCB after step (2.1); and (2.3) after step (2.2), immersing said PCB in a second solution comprising sulfuric acid and applying ultrasonic agitation to said second solution during said immersion.
- 4. The method of claim 3 wherein said copper portions of said PCB have minimum spacing of at least 5 mils, and wherein said first sulfuric acid solution comprises 10% sulfuric acid and said second sulfuric acid solution comprises 5% sulfuric acid.
- 5. The method of claim 3 wherein said copper portions of said PCB have minimum spacing of less than 5 mils, and wherein said first sulfuric acid solution comprises 1% sulfuric acid and said second sulfuric acid solution comprises 5% sulfuric acid.
- 6. The method of claim 3 wherein step (3) is performed after step (2.2) without an intermediate rinsing step.
- 7. The method of claim 3 wherein step (2.2) comprises spraying said PCB with nitrogen and de-ionized water for a period of time, and commencing said step with said PCB oriented at a 90° angle to the floor and gradually rotating it to a 45° angle to the floor during said period of time.
- 8. The method of claim 2 wherein step (3) comprises immersing said PCB in a solution comprising palladium and applying ultrasonic agitation to said solution during said immersion.
- 9. The method of claim 8 wherein said palladium solution further comprises sulfuric acid and wherein step (3) comprises applying said ultrasonic agitation for 5 second period at 30 second intervals.
- 10. The method of claim 8 wherein step (3) further comprises orienting said PCB at a first 45° angle to said floor for approximately half of a duration of said step and then flipping said PCB to a second 45° angle to said floor for a remainder of said step.
- 11. The method of claim 9 wherein step (3) is performed at about 30° C. and for about 3 minutes.
- 12. The method of claim 1 further comprising the step of: (7) between steps (3) and (4), immersing said PCB in a solution of about 1% sulfuric acid.
- 13. The method of claim 2 wherein step (4) comprises the steps of: immersing said PCB in a solution of electroless nickel, said PCB oriented at an angle of 45° to the floor; and mechanically agitating said PCB while in said solution.
- 14. The method of claim 13 wherein step (4) is performed with said solution at 80° C. and wherein said mechanical agitation is continual.
- 15. The method of claim 13 wherein step (4) further comprises the steps of: determining if said copper portions of said PCB have been fully covered with nickel; immersing said PCB in a solution comprising hydrochloric acid; rinsing said PCB with de-ionized water; if said copper portions of said PCB have not been fully covered with nickel, repeating steps (3) and (4) prior to proceeding to step (5).
- 16. The method of claim 15 wherein step (4) further comprises the step of, prior to repeating steps (3) and (4), immersing said PCB in a third solution comprising sulfuric acid and applying ultrasonic agitation to said third solution during said immersion.
- 17. The method of claim 15 wherein said step of determining if said copper portions of said PCB have been fully covered comprises visually inspecting said copper portions of said PCB.
- 18. The method of claim 1 wherein step (5) comprises immersing said PCB in a solution comprising electroless gold at about 90° C. and having a pH of about 4.5 to about 4.7.
- 19. The method of claim 18 wherein step (5) is performed for a period sufficient to deposit a layer of gold of about 6 to about 8 micro-inches on said copper portions of said PCB.
- 20. The method of claim 2 wherein step (6) comprises immersing said PCB in a solution comprising autocatalytic gold at about 70° C. with said PCB oriented at 90° to the floor.
- 21. The method of claim 20 wherein no agitation of said solution or said PCB is applied during step (6).
- 22. The method of claim 21 wherein said PCB is immersed in said autocatalytic gold solution for a time sufficient to deposit about 40 micro-inches of additional gold on said copper portions of said PCB.
- 23. The method of claim 2 further comprising the steps of rinsing said PCB after each of steps (2), (3), (4), (5), and (6).
- 24. The method of claim 23 wherein said rinsing steps comprise rinsing said PCB in a beaker with overflowing de-ionized water.
- 25. A method of electrolessly gold plating copper portions on a printed circuit board (PCB), said method comprising the steps of:
(1) cleaning said PCB, said cleaning including immersing said PCB in a cleaning solution and applying ultrasonic agitation to said cleaning solution; (2) spraying said PCB with nitrogen and de-ionized water for a period of time, and commencing said step with said PCB oriented at a 90° angle to the floor and gradually rotating it to a 45° angle to the floor during said period of time. (3) immersing said PCB in a first solution comprising sulfuric acid and applying ultrasonic agitation to said first solution during said immersion; (4) rinsing said PCB with overflowing de-ionized water; (5) immersing said PCB in a second solution comprising sulfuric acid and applying ultrasonic agitation to said second solution during said immersion; (6) immersing said PCB in a solution comprising palladium and applying ultrasonic agitation to said solution during said immersion; (7) rinsing said PCB with overflowing de-ionized water; (8) immersing said PCB in a 1% solution of sulfuric acid; (9) immersing said PCB in a solution of electroless nickel, said PCB oriented at an angle of 45° to the floor and mechanically agitating said PCB while in said solution; (10) rinsing said PCB with overflowing de-ionized water; (11) determining if said copper portions of said PCB have been fully covered with nickel; (12) immersing said PCB in a solution comprising hydrochloric acid; (13) rinsing said PCB with de-ionized water; (14) if said copper portions of said PCB have not been fully covered with nickel, repeating steps (5) through (13); (15) electrolessly plating said copper portions with a first layer of gold; (16) rinsing said PCB with overflowing de-ionized water; (17) autocatalytically plating said copper portions with a second layer of gold with no agitation; and (18) rinsing said PCB with overflowing de-ionized water.
- 26. The method of claim 25 wherein said copper portions of said PCB have minimum spacing of at least 5 mils, and wherein said first sulfuric acid solution comprises 10% sulfuric acid and said second sulfuric acid solution comprises 5% sulfuric acid.
- 27. The method of claim 25 wherein said copper portions of said PCB have minimum spacing of less than 5 mils, and wherein said first sulfuric acid solution comprises 1% sulfuric acid and said second sulfuric acid solution comprises 5% sulfuric acid.
- 28. The method of claim 25 wherein step (6) is performed after step (5) without an intermediate rinsing step.
- 29. The method of claim 28 wherein said palladium solution further comprises sulfuric acid and wherein step (6) comprises applying said ultrasonic agitation for 5 second periods at 30 second intervals.
- 30. The method of claim 28 wherein step (6) further comprises orienting said PCB at a first 45° angle to said floor for approximately half of a duration of said step and then flipping said PCB to a second 45° angle to said floor for a remainder of said step.
- 31. The method of claim 30 wherein step (6) is performed at about 30° C. and for about 3 minutes.
- 32. The method of claim 31 wherein step (9) is performed with said solution at 80° C. and wherein said mechanical agitation is continual.
- 33. The method of claim 32 wherein step (11) comprises visually inspecting said copper portions of said PCB.
- 34. The method of claim 33 wherein step (15) comprises immersing said PCB in a solution comprising electroless gold at about 90° C. and having a pH of about 4.5 to about 4.7.
- 35. The method of claim 34 wherein step (15) is performed for a period sufficient to deposit a layer of gold of about 6 to about 8 micro-inches on said copper portions of said PCB.
- 36. The method of claim 35 wherein step (17) comprises immersing said PCB in a solution comprising autocatalytic gold at about 70° C. with said PCB oriented at 90° to the floor.
- 37. The method of claim 36 wherein no agitation of said solution or said PCB is applied during step (15).
- 38. The method of claim 37 wherein, in step (17), said PCB is immersed in said autocatalytic gold solution for a time sufficient to deposit about 40 micro-inches of additional gold on said copper portions of said PCB.
- 39. The method of claim 25 further comprising the step of: (19) blow drying said PCB with dry Nitrogen.
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. provisional application No. 60/281,146, filed on Apr. 3, 2001, which is hereby incorporated by reference in its entirety.
Provisional Applications (1)
|
Number |
Date |
Country |
|
60281146 |
Apr 2001 |
US |