Tarnish Inhibiting Composition for Metal Leadframes
An aqueous tarnish inhibiting solution comprising a mercapto carboxylic acid and a corrosion inhibitor to produce an anti-tarnish layer on metal surfaces, such as silver plated copper leadframes and a method of using the same is provided. The composition provides an improved anti-tarnish layer that does not affect wirebondability or the adhesion of a mold compound to a leadframe.
1 . An aqueous tarnish inhibiting composition comprising a mercapto carboxylic acid and a corrosion inhibitor.
2 . The aqueous tarnish inhibiting composition according to claim 1 , wherein the mercapto carboxylic acid is a long-chain mercapto alkyl carboxylic acid.
3 . The aqueous tarnish inhibiting composition according to claim 1 , wherein the mercapto carboxylic acid is selected from the group consisting of mercaptoundecanoic acid, mercaptohexadecanoic acid, mercaptododecanoic acid, mercapto hexanoic acid, mercaptopentadecanic acid and (mercaptomethyl)cyclopropaneacetic acid.
4 . The aqueous tarnish inhibiting composition according to claim 3 , wherein the corrosion inhibitor is selected from the group consisting of azoles, imidazoles, triazoles, indoles, thiazoles and tetrazoles.
5 . The aqueous tarnish inhibiting composition according to claim 3 , wherein the corrosion inhibitor comprises a benzotriazole.
6 . The aqueous tarnish inhibiting composition according to claim 1 , further comprising a buffer.
7 . The aqueous tarnish inhibiting composition according to claim 6 , wherein the buffer is an alkali carbonate metal salt.
8 . The tarnish inhibiting composition according to claim 7 , wherein the alkali carbonate metal salt comprises sodium carbonate or potassium carbonate.
9 . The tarnish inhibiting composition according to claim 1 , wherein the mercapto carboxylic acid is present in the composition at a concentration of between about 0.01 g/L and about 10 g/L.
10 . The tarnish inhibiting composition according to claim 9 , wherein the mercapto carboxylic acid is present in the composition at a concentration of between about 0.5 g/L and about 2 g/L.
11 . The tarnish inhibiting composition according to claim 1 , wherein the corrosion inhibitor is present in the composition at a concentration of between about 0.1 g/L and about 5 g/L.
12 . The tarnish inhibiting composition according to claim 11 , wherein the corrosion inhibitor is present in the composition at a concentration of between about 0.5 g/L and about 2 g/L.
13 . The tarnish inhibiting composition according to claim 6 , wherein the buffer is present in the composition at a concentration of between about 2.0 g/L and about 20 g/L.
14 . A process for reducing tarnish on a metal surface, said metal surface comprising at least one of silver and copper, the process comprising the step of:
contacting the metal surface with a composition comprising a mercapto carboxylic acid and a corrosion inhibitor to produce an anti-tarnish layer thereon.
15 . The process according to claim 14 , wherein the metal surface comprises silver and the anti-tarnish layer prevents silver tarnish.
16 . The process according to claim 14 , wherein the mercapto carboxylic acid is a long chain mercapto alkyl carboxylic acid.
17 . The process according to claim 16 , wherein the mercapto carboxylic acid is selected from the group consisting of mercaptoundecanoic acid, mercaptohexadecanoic acid, mercaptododecanoic acid, mercapto hexanoic acid, mercaptopentadecanic acid and mercaptomethyl)cyclopropaneacetic acid.
18 . The process according to claim 14 , wherein the corrosion inhibitor is selected from the group consisting of azoles, imidazoles, triazoles, indoles, thiazoles and tetrazoles.
19 . The process according to claim 14 , wherein the corrosion inhibitor comprises a benzotriazole.
20 . The process according to claim 14 , further comprising a buffer.
21 . The process according to claim 20 , wherein the buffer is an alkali carbonate metal salt.
22 . The process according to claim 21 , wherein the alkali carbonate metal salt comprises sodium carbonate or potassium carbonate.
23 . The process according to claim 14 , wherein the mercapto carboxylic acid is present in the composition at a concentration of between about 0.01 g/L and about 10 g/L.
24 . The process according to claim 23 , wherein the mercapto carboxylic acid is present in the composition at a concentration of between about 0.5 g/L and about 2 g/L.
25 . The process according to claim 14 , wherein the corrosion inhibitor is present in the composition at a concentration of between about 0.1 g/L and about 5 g/L.
26 . The process according to claim 25 , wherein the corrosion inhibitor is present in the composition at a concentration of between about 0.5 g/L and about 2 g/L.
27 . The process according to claim 20 , wherein the buffer is present in the composition at a concentration of between about 2.0 g/L and about 20 g/L.
28 . The process according to claim 14 , wherein the peel strength of the metal surface following the application of the anti-tarnish layer is substantially equal to the peel strength of the metal surface prior to the application of the anti-tarnish layer.
29 . The process according to claim 14 , wherein the peel strength of the metal surface following the application of the anti-tarnish layer is greater than the peel strength of the metal surface prior to the application of the anti-tarnish layer.
30 . The process according to claim 14 , wherein the application of the anti-tarnish layer to the metal surface prevents deterioration of wirebondability during an annealing process.
31 . A leadframe panel coated by the process of claim 14 .
32 . The leadframe panel according to claim 31 , wherein the peel strength of the metal surface following the application of the anti-tarnish layer is substantially equal to the peel strength of the metal surface without application of the anti-tarnish layer.