How to control Thickness Variation with Electroform Nickel

adv.  

We are plating nickel deposits that are 24 inches by 24 inches by 0.006 inches thick and need to control the thickness variation to ± 5% or less.

The bath is a typical Nickel sulphate, Nickel Chloride, Boric Acid bath with a pH of 4.0 and a temperature of 40 degrees C. The Current density is about 17 amps per square foot.

We use a bath change rate of 15 times per hour to provide high agitation.

The control problem is aggravated greatly ( + 10 and + 20% )in areas where where we have to plate nickel around pillars of photo resist that might have as many as 400 pillars 0.012 inches in diameter spread uniformly over a square area that is only 0.4 inches by 0.4 inches.

Is this a common problem?

Are there any techniques that will help reduce the variation ?

Thank you

Ronald

Your problem is very familiar to most electroformers. the first step is to make sure that the exposed anode area is slightly smaller than the electroform. The next step is to use a shield in between the anode or cathode or to use a robber around the electroform.

Hope this helps

adv.