Increasing plating speed with agitation, eductors, or non-aqueous baths
A discussion started in 2003 but continuing through 20192003
Q. A client is interested in increasing the speed of copper plating prior to buffing. Does anyone have experience with the use of educators for this purpose?BERT SHERWOOD
- LOS ANGELES, California, USA
A. To a point, increasing solution agitation will clear away the "barrier zone" or "diffusion layer", the area that is a few millionths of an inch thick where all of the metal ions have plated out and the pH has changed slightly. Stronger agitation allows new metal ions to get to the substrate faster than by the diffusion process. Result - You can use a higher current density without burning. Look at the turbulence they use on high current density plating on wire or continuous coil plating. Educators will help to a point, but only to a point. The faster you plate, the more sensitive the operation gets because every piece must receive a given amount of agitation. Racking has to get very good for this. Can you gain a few percent in plate rate? Quite possibly. Will educators be enough ? Maybe.James Watts
- Navarre, Florida
June 4, 2013
Q. I am plating in a lab setting with a 250 ml beaker of copper sulfate and sulfuric acid.
I am reading in several articles that agitation of the beaker to increase the flow of ions to the diffusion barrier is important. To what extent (speed of the stir bar) is agitation effective. I always set it to about half the maximum speed on the stir plate. However, is there an optimal speed for agitation?
- Wilmington, New York
June 5, 2013
A. Hi Luke. The short answer is that you can rarely have too much agitation, so I'd try turning it up.
The longer answer is that agitation does two basic things:
1. It assures general solution homogeneity, i.e., that the temperature and solution concentration is the same throughout. That's very important in deep tanks, or where the process generates a lot of heat like in hard anodizing, and for even plating thickness, and to prevent burning at high plating speeds, etc.
2. As James notes above, agitation can thin the boundary layer. If you were able to actually microscopically see the dynamics going on in a plating cell, you'd see that once you are a very short distance from the anode, and until you get very close to the cathode, not much is happening. Ions are migrating through the solution from anode to cathode, but the solution is quite uniform, and that's about it. However, once you get really close to the cathode, the magic starts happening as ions are reduced to metal. As one ion is converted, another must get across the zone for the process to continue, the pH must correct itself, etc. I don't pretend to deeply understand the situation, but the trip across this zone is slow and difficult; so extreme agitation, such as jet plating on reel-to-reel electronic strip components, which provides turbulence all the way to the cathode, can greatly thin that boundary layer, allowing much higher plating speeds.
I doubt that you'll actually see any difference in mid-speed and high speed stirring in a beaker though.
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha
Increasing Electroplating SpeedOctober 20, 2015 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread
Q. I am interested in learning more about electroplating. In my research, I can't seem to find the answer to a few questions involving the limitations of electroplating with respect to plating speed. Could someone please tell me why either or both of these methods would not be successful in increasing the speed of electroplating.
1. When plating a relatively small object, consider having two additional electrodes with much larger surface areas submerged in the plating solution. These electrodes could have a potential between them to constantly saturate the plating solution and allow for higher plating rates on the substrate. This could possibly be done by removing potential from the substrate to quickly recharge the solution with the large electrodes and then quickly discharge the solution's ions on the substrate. This could also potentially be done with carefully controlled potentials between the two electrodes and the substrate.
2. Are there non-aqueous solutions that would resist dissociation such as that that occurs with hydrogen atoms when using aqueous solutions? Would this allow for a faster plating rate that avoids "burning"? I'm thinking of a special oil formulation or perhaps some type of liquid metal solution using something like gallium? I realize there are external considerations such as environmental issues and sourcing issues but I'm primarily interested in physical limitations.
Any help in answering these questions is greatly appreciated.
Hobbyist - Indianapolis, Indiana USA
A. Hi Aaron. I think the biggest trick to increased plating speed is extreme agitation to thin the boundary layer. I've heard of plating speeds about 10X the conventional limit on strip plating when a high pressure jet of plating solution is pumped against it.
Sorry, I don't know what limits apply when molten salts, ionic solutions, or organic electrolytes are employed instead of aqueous solutions.
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha
April 17, 2018
Q. I am also very interested in the speed limitations for plating and would like to understand the theoretical route to achieving deposition rates of ~1 um/s. Aaron Tolly asked the same questions I had regarding non-aqueous electrolytes or methods to increase the concentration of ions near the boundary layer.
What is the best deposition rate you are aware of (in um/s) and can anyone speak to the theoretical and practical process limitations (or suggest an expert in the field I could contact)? My current understanding is that .1 um/s is very good and perhaps representative of the fluid impingement deposition method?
- Raleigh, North Carolina, USA
July 31, 2019
Q. I am copper plating thin film using two anodes, one on either side. I am using a magnetic stirrer directly beneath the thin film cathode. I found that stirring at relatively high RPM (600+) produces uneven coating thicknesses. The coating grows preferentially on the edge of one side and on the opposite edge for the other side. I realized that this is caused by centrifugal forces pushing the copper cations off to the opposite edge on both surfaces. A reduced stirring rate (200 RPM) eliminated this effect. In summary, increasing the agitation for faster plating can have adverse effects on throwing power.
If anyone has established settings for copper plating relatively thick (200 µ) dense coatings please reply. Many Thanks, PaulPaul Moroney
Metallurgy - Limerick, Ireland