Controlling the hardness of electrodeposited copper coatings by variation of current profile
View Patent ↗Pulse reverse electrolysis of acid copper solutions is used for applying copper deposits of a controlled hardness for applications such as producing printing cylinders. The benefits include improved production capacity. Hardness of the deposit is controlled by varying at least one factor selected from the group consisting of (i) cathodic pulse time, (ii) anodic pulse time, (iii) cathodic pulse current density, and (iv) anodic pulse current density. Preferably the ratio of cathodic pulse time to anodic pulse time is varied.
1. A method of electroplating an article in an acidic copper electroplating bath comprising the steps of:
(a) suspending said article in the acidic copper electroplating bath;
(b) plating said article for a period of time with a pulse-reverse current profile to produce a desired thickness of copper on the surface of said article;
wherein the hardness of the plated copper is controlled to a level between about 89 and 208 HV 50 by controlling the ratio of cathodic pulse time to anodic pulse time or cathodic pulse current density to anodic pulse current density, wherein the acidic copper electroplating bath comprises a hardening agent comprising a sulfur (II) compound, and a Polyalkylene glycol and wherein the plated copper is softer than copper plated from the same electroplating bath under direct current plating.
2. The method according to claim 1 , wherein the electroplating bath comprises copper ions at a concentration of about 12-75 g/l and sulfate counter ions.
3. The method according to claim 2 , wherein the electroplating bath comprises sulphuric acid (98% by wt.) at a concentration of about 25-200 ml/l.
4. The method according to claim 2 , wherein the electroplating bath comprises chloride ions at a concentration of about 10-500 mg/l.
5. The method according to claim 1 , wherein the plating bath further comprises a material selected from the group consisting of wetting agents, brighteners, and levelers.
6. The method according to claim 1 , wherein the pulse plating current profile consists of alternating cathodic and anodic pulses.
7. The method according to claim 6 , wherein the cathodic pulse time is 2 -100 ms.
8. The method according to claim 6 , wherein the anodic pulse time is 0.1 -10 mns.
9. The method according to claim 6 , wherein the pulse profile further comprises a cathodic period of extended time.
10. The method according to claim 9 , wherein the extended cathodic pulse is up to 1 hour.
11. The method according to claim 6 , wherein the pulse profile comprises a period of zero current between the cathodic and anodic pulses.
12. The method according to claim 1 , wherein the average applied current density is 1.0-35.0 A/dm 2 .
13. The method according to claim 12 , wherein the current density during the anodic pulse is between 0 and 5 times the current density during the cathodic pulse.
14. The method according to claim 1 , wherein the forward pulse time is about 10 mns, the reverse pulse time is between about 1.0 and 1.5 ms, and the reverse/forward current ratio is about 2:1 to control the hardness to between about 89 and 104 HV 50 .
15. The method according to claim 1 , wherein the article to be plated is a gravure printing cylinder.