Silver plating in electronics manufacture
View Patent ↗Compositions and methods for silver plating onto metal surfaces such as PWBs in electronics manufacture to produce a silver plating which is greater than 80 atomic % silver, tarnish resistant, and has good solderability.
1. A process for Ag plating a metal surface comprising:
contacting the metal surface with a composition comprising a source of Ag ions, a modulating agent comprising an alkylene polyamine polyacetic acid compound, and water; and
forming by immersion displacement a Ag-based coating on the metal surface, wherein the ionic content of the composition is such that it has a room temperature conductivity below about 10 mS/cm, the composition has a pH between 1 and about 3, and the Ag-based coating comprises at least about 80 atomic % Ag (bulk average).
2. The process of claim 1 wherein the modulating agent comprises an alkylene polyamine polyacetic acid compound from a alkaline earth/alkali metal-free source of alkylene polyamine polyacetic acid compound.
3. The process of claim 1 wherein the modulating agent comprises N-(2-hydroxyethyl)ethylenediamine triacetic acid.
4. The process of claim 1 wherein the modulating agent comprises N-(2-hydroxyethyl)ethylenediamine triacetic acid from an alkaline earth/alkali metal-free source of N-(2-hydroxyethyl)ethylenediamine triacetic acid.
5. The process of claim 1 wherein the modulating agent comprises N-(2-hydroxyethyl)ethylenediamine triacetic acid and the composition has a pH between 1 and about 2.
6. The process of claim 1 wherein the composition further comprises an ethylene oxide/propylene oxide block co-polymer additive.
7. The process of claim 6 wherein the ethylene oxide/propylene oxide block co-polymer has a unit ratio of PO:EO of about 3:4.
8. The process of claim 6 wherein the ethylene oxide/propylene oxide block co-polymer has a unit ratio of PO:EO of 3:4 +/−10%.
9. The process of claim 6 wherein the ethylene oxide/propylene oxide block co-polymer has a unit ratio of PO:EO of about 5:3.
10. The process of claim 6 wherein the ethylene oxide/propylene oxide block co-polymer has a unit ratio of PO:EO of 5:3 +/−10%.
11. The process of claim 6 wherein the composition has a room temperature conductivity below about 5 mS/cm.
12. The process of claim 11 wherein the ethylene oxide/propylene oxide block co-polymer has a unit ratio of PO:EO of about 3:4.
13. The process of claim 11 wherein the ethylene oxide/propylene oxide block co-polymer has a unit ratio of PO:EO of 3:4 +/−10%.
14. The process of claim 11 wherein the ethylene oxide/propylene oxide block co-polymer has a unit ratio of PO:EO of about 5:3.
15. The process of claim 11 wherein the ethylene oxide/propylene oxide block co-polymer has a unit ratio of PO:EO of 5:3 +/−10%.
16. The process of claim 1 wherein the ionic content of the composition is such that it has a room temperature conductivity below about 5 mS/cm.
17. The process of claim 16 wherein the modulating agent comprises an alkaline earth/alkali metal-free source of the alkylene polyamine polyacetic acid compound.
18. The process of claim 16 wherein the modulating agent comprises N-(2-hydroxyethyl)ethylenediamine triacetic acid.
19. The process of claim 16 wherein the modulating agent comprises N-(2-hydroxyethyl)ethylenediamine triacetic acid from an alkaline earth/alkali metal-free source of N-(2-hydroxyethyl)ethylenediamine triacetic acid.
20. The process of claim 16 wherein the modulating agent comprises N-(2-hydroxyethyl)ethylenediamine triacetic acid and the composition has a pH between 1 and about 2.
21. The process of claim 1 wherein the Ag-based coating comprises at least about 90 atomic % Ag (bulk average).
22. The process of claim 1 wherein the metal surface comprises a printed wiring board substrate comprising electrical interconnect recesses and further comprising the step of mechanically assisting the Ag plating composition into the electrical interconnect recesses, thereby forming by immersion displacement a Ag-based coating on the Cu surface, wherein the mechanically assisting the Ag plating composition into the electrical interconnect recesses comprises contacting the Cu surface with a brush, sponge, or squeegee to brush the Ag plating composition into the electrical interconnect recesses.
23. The process of claim 1 wherein the alkylene polyamine polyacetic acid compound is present in an concentration between 1 g/L and about 35 g/L.
24. The process of claim 1 wherein the alkylene polyamine polyacetic acid compound is present in an concentration between 5 g/L and about 25 g/L.
25. The process of claim 1 wherein the alkylene polyamine polyacetic acid compound is present in an concentration between 8 g/L and about 15 g/L.
26. A process for depositing a Ag-based coating over a surface of a copper conducting layer in a printed wiring board substrate, the process comprising:
contacting the metal surface with a composition comprising:
a) a source of Ag ions;
b) an alkylene polyamine polyacetic acid compound;
c) water; and
d) 3,5-dinitrohydroxybenzoic acid;
wherein the ionic content of the composition is such that it has a room temperature conductivity below about 25 mS/cm the composition has a pH between 1 and about 3; and
forming by immersion displacement a Ag-based coating comprising at least about 80 atomic % Ag (bulk average) on the metal surface.
27. The process of claim 26 wherein the alkylene polyamine polyacetic acid compound is N-(2-hydroxyethyl)ethylenediamine triacetic acid.
28. The process of claim 26 wherein the alkylene polyamine polyacetic acid compound is an alkaline earth/alkali metal-free source of N-(2-hydroxyethyl)ethylenediamine triacetic acid.
29. The process of claim 26 wherein the composition further comprises an ethylene oxide/propylene oxide block co-polymer.
30. The process of claim 26 wherein the alkylene polyamine polyacetic acid compound is present in an concentration between 1 g/L and about 35 g/L.
31. The process of claim 26 wherein the alkylene polyamine polyacetic acid compound is present in an concentration between 5 g/L and about 25 g/L.
32. The process of claim 26 wherein the alkylene polyamine polyacetic acid compound is present in an concentration between 8 g/L and about 15 g/L.
33. A process for depositing a Ag-based coating over a surface of a copper conducting layer in a printed wiring board substrate, the process comprising:
contacting the metal surface in the printed wiring board substrate with a composition comprising:
a) a source of Ag ions;
b) an alkylene polyamine polyacetic acid compound;
c) an ethylene oxide/propylene oxide block co-polymer additive; and
d) water; and
wherein the ionic content of the composition is such that it has a room temperature conductivity below about 25 mS/cm and the composition has a pH between 1 and about 3; and
forming by immersion displacement a Ag-based coating comprising at least about 80 atomic % Ag (bulk average) on the metal surface.
34. The process of claim 33 wherein the ethylene oxide/propylene oxide block co-polymer has a unit ratio of PO:EO of about 3:4.
35. The process of claim 33 wherein the ethylene oxide/propylene oxide block co-polymer has a unit ratio of PO:EO of 3:4 +/−10%.
36. The process of claim 33 wherein the ethylene oxide/propylene oxide block co-polymer has a unit ratio of PO:EO of about 5:3.
37. The process of claim 33 wherein the ethylene oxide/propylene oxide block co-polymer has a unit ratio of PO:EO of 5:3 +/−10%.
38. The process of claim 33 wherein the composition comprises an alkaline earth/alkali metal-free source of the alkylene polyamine polyacetic acid compound; and
wherein the composition is free of added alkaline earth metal ions and alkali metal ions.
39. The process of claim 38 wherein the alkylene polyamine polyacetic acid compound is N-(2-hydroxyethyl)ethylenediamine triacetic acid.
40. The process of claim 39 wherein the Ag based coating is at least about 90 atomic % Ag (bulk average).
41. The process of claim 39 wherein the Ag based coating is at least about 95 atomic % Ag (bulk average).
42. The process of claim 38 wherein the Ag based coating is at least about 90 atomic % Ag (bulk average).
43. The process of claim 33 wherein the alkylene polyamine polyacetic acid compound is present in an concentration between 1 g/L and about 35 g/L.
44. The process of claim 33 wherein the alkylene polyamine polyacetic acid compound is present in an concentration between 5 g/L and about 25 g/L.
45. The process of claim 33 wherein the alkylene polyamine polyacetic acid compound is present in an concentration between 8 g/L and about 15 g/L.
46. A process for Ag plating a Cu surface of a printed wiring board substrate comprising:
contacting the Cu surface with a composition comprising:
a) a source of Ag ions;
b) N-(2-hydroxyethyl)ethylenediamine triacetic acid;
c) an ethylene oxide/propylene oxide block co-polymer additive;
d) a tarnish inhibitor; and
e) water;
wherein the composition has pH between 1 and about 3, and a room temperature conductivity of less than about 25 mS/cm; and
forming by immersion displacement a Ag-based coating on the metal surface which comprises at least about 90 atomic % Ag (bulk average).
47. The process of claim 46 wherein the N-(2-hydroxyethyl)ethylenediamine triacetic acid is present in an concentration between 1 g/L and about 35 g/L.
48. The process of claim 46 wherein the N-(2-hydroxyethyl)ethylenediamine triacetic acid is present in an concentration between 5 g/L and about 25 g/L.
49. The process of claim 46 wherein the N-(2-hydroxyethyl)ethylenediamine triacetic acid is present in an concentration between 8 g/L and about 15 g/L.