Agitating Plating Process Tanks

Q. What is the best way to agitate plating process tanks? One of our chemical vendors suggested that the agitation in our tanks is not “up to snuff.” What are your thoughts on this?—K.M.

A. I agree 100 percent with your chemical vendor that good agitation is important in good quality plating.
The classic way to agitate plating solutions has been either air agitation or, to a lesser extent, cathode reciprocation. An older paper that is difficult to find, Exploitation of Eductors Agitation in Copper Electroplating, by D.R. Gabe, M. Ward and J.N. Crosby, presented at the June 1999 Sur/Fin, addressed the question of efficient agitation methods. Using a mathematical relationship that we needn’t concern ourselves with here, the following enhancement factors were determined.

Agitation Method	Enhancement Factor
Static solution	1
Natural convection	1-2
Cathode reciprocation	2-4
Air agitation	2-5
Vibratory	3-30
Turbulent flow	5-25
Ultrasonics	2-10

As you see from the data, the agitation method does make a difference. Surprisingly, the two standard methods, cathode reciprocation and air agitation, give similar enhancement factors. The data also indicate that the vibratory and turbulent flow methods of agitation offer real improvement over the two classic methods. The vibratory method is usually not used in the plating industry; rather, the turbulent flow method is used.

The use of eductors gives you a turbulent flow environment, and based on the information in the table, much better mixing compared with cathode reciprocation or air agitation. An eductor is a specially designed nozzle that causes liquid pumped through the nozzle to exit at high velocity. This in turns pulls additional solution from the surrounding region through the nozzle. 

I recommend eductor-based agitation systems. More information on the process and vendors who sell the eductor nozzles can be found at PFonline.com.