The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Spots in Ag Plating

2005

Hello,

We are getting white spots in our Ag-plated caps. These caps are barrel plated. The base material is Carpenter steel (Fe-Ni). The base is treated with Ni and Cu strikes prior to plating. Here is some background:

The spots have a definite geometric shape: mostly elliptical and sometimes rectangular.

XPS determined the thickness in the spotted regions is less than that found in the "non-defective" region.

SEM analysis revealed that the defective areas were not "filled in" and subsequently rough. Skip sites (poor nucleated regions) were found on some defective samples.

Base analysis revealed the presence of silicon oxide contamination in a non-geometric pattern. In addition, trials where we marked the contamination on the base prior to plating revealed that the defect occurred in a different spot on the base. (not good).

The base goes though a Alkaline Cleaning and 50% Vol HCl Activation dip.

My question is this. Can plating bath chemistry cause these "geometrically" shaped spots in the barrel plating process? My thinking is that if it is a chemistry problem the spots would have a non-geometric shape. I would think this type of defect needs a template. What kind of template could cause these geometric shapes? Also, are these types of defects common in barrel plating processes? Thanks for any help.

Luke Autry
Materials / Electrochemical Engineer - CT

---

Mr.Luke
please make sure the job being caps are not struck together in the barrel, a sort of masking.As the masking some times may not be continues as the barrel tumbles may result in different shape of miss plating or less thickness plating.If the plating media is not silver,u could have used cleaned SS balls in the barrels along with your job. The advantage of using SS balls is that SS (Stainless Steel) will not accept adhered coating with out specific pre-treatment.This will help your cap to not to stick.
in your letter you mentioned that you do nickel and copper under coat.Is it not the other way, i.e., Copper and Nickel!

T.K. Mohan
plating process supplier - Mumbai, India
2005

---

Is the 50% HCl pulling the silicon out of the steel?

Or is the 50% HCl inadequate to activate nickel-steel?

Try 20% HCl for 30 seconds followed by a Nickel Chloride Strike.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2005

I wonder if one could use ceramic balls to keep the caps from sticking?

Luke Autry
- Ellington, Connecticut, USA
2005

---

Perhaps you should be suspect of your Ni Activator. You should check for Cu contamination. Is your Activator a hot tank? Also,is your post-rinse after Ni strike clean? In my experience as a plater on a silver plating line, contamination can really put a kink in things and should be looked at first rather than last. Good Luck!

Regards,

Michael Null
- Methen, MA, United States
2005