Pits on Chrome-plated ABS parts

A. Manish,

It is likely you are using cheap Phosphorous Copper anodes. Check an anode from the bath. If there are holes and sockets, this indicates casting defects; and please note, that's the copper powder from the holes in the anode which is walking all over producing roughness.

Change the anodes and use standard Phosphorous Cu anodes from a reputed supplier. Pitting is caused by a lack of Carrier. Or Nitric acid in solution. Or poor air agitation.

Electroless Ni faults also show up like pitting.

An Acid Copper Dull 3 minute strike is highly recommended after EN before Bright acid Copper.

You need a chiller in summer or the brightener breakdown products can affect leveling and LCD. Run copper at 25 to 30 °C. Delhi is usually 40 °C in the shade at 11 am. So the chiller is the savior.

Give your father my regards. Hope this helps.

A. Sorry this response is late! But it still may help manufacturers in the future!

1st of all, when trouble shooting, do not assume that the defect is automatically the result of your process.
As a QA Engineer, a few years ago I had an inner front grill (automotive) that was molded of ABS plastic then was chromed. We found many dirt-like defects in the chrome as well as pitted defects. When I started my investigation, I would cut out a 1 inch to two inch square around the defect with sharp hand cutters. I would then take the cutters and peel back the Chrome, To my surprise, The defect was 85% of the time in the plastic telegraphing through the chrome. When ABS PLASTIC is molded it is hot or warm coming out of the molding machine; when laid on a table top or other abrasive surface to be trimmed, it can be scuffed up -- and after plating or chroming, the defect will look to be in the chrome! Same with pitting in the plastic. These defects in the plastic may or may not be seen with the naked eye!

Good luck to you all!

Sincerely,

A. It does sound like a molding issue, but I don't have much experience in that. As for the plating, I can only suggest that you consider lengthening the nickel plating time rather than the copper time because nickel offers some self-leveling in a way that copper doesn't.

"Standards and Guidelines for Electroplated Plastics"
by American Society for Electroplated Plastics

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A. The usual way of plating ABS is to etch the surface to remove the butadiene and leave micropits. These pits act as a key to hold the subsequent metallising layers. From your description it sounds like two possible problems. The first one is that you are not using electroplating grade ABS, so there is too much "B" in the blend. Secondly, if the ABS is the correct grade, the moulding conditions could be wrong, as Ted says. This can result in the outer "skin" of the moulding having a different composition to the bulk polymer. Usually this is not a problem, but clearly in this case it could be! I am not a moulding expert, so I would suggest you ask someone who is how to reduce the amount of butadiene in the outer layer. I suspect it will be simply to do with mould temperatures and cooling rates, but as I say ...

A. Looks like the pits may be due to gas bubbles. Could be due to inadequate agitation and/or inadequate wetting.

A. YES, MOULDING PROBLEM. FOR GOOD QUALITY PLATING, SPECIAL PLATING GRADE ABS MOULDING COMPOUNDS ARE PREFERRED. PROCESS SEQUENCE WHICH I HAVE OBSERVED.

BUFFING
ALKALINE CLEANING
W.R
ACID DIP sulfurIC ACID.
W.R
ETCHING , CHROMIC ACID + sulfurIC ACID, AIR AGITATION, TEMPERATURE 55 TO 70 °C.
W.R
W.R
W.R
HCl DIP
W.R
PRE ACTIVATION
ACTIVATION palladium + TIN
W.R
POST ACTIVATION
W.R
ELECTROLESS NICKEL
W.R
JIGGING
ACTIVATION ACID
W.R
COPPER PLATING, ETC.,

NOTE: ETCHING STAGE IS VERY IMPORTANT, 80% OF PROBLEMS GET SOLVED IF THIS STAGE IS DONE PROPERLY. DURING MOULDING GAS BUBBLES GETS TRAPPED IN ETCHING THEY BECAME PIN HOLES. SO BUFFING SOLVES THIS PROBLEM.

A. Hi Feras. In some cases the platers rack the parts only once and convey them through all the steps without re-jigging. But in other cases (which you and I are less familiar with) platers rack the parts for electroless nickel plating, and then re-rack them in a different fashion for the electrolytic processes. Presumably, Ajay is describing the latter case.

Regards,

Hi Ricardo. Readers are encouraged to help you, and I hope they do. Still, with all the Q & A's on this page, and dozens of similar pages here which deal with defects in chrome plating of plastics as an introduction to the breadth of the subject, I don't think you'll get that book written short of retaining a consultant to do it :-)

Just in the first 20 seconds of thinking about it, we have blisters and peeling, stardusting, whitewash, pitting, incomplete plating coverage, nickel show, rack marks, staining ... and hopefully folks will remind me of a few others :-)

Luck and Regards,

A. Hi Asghar,

Common causes of acid copper pitting are high current density, air entrapment in filtration, improper cleaning or residue remaining on surface, organic contamination. You may reduce current density, release air entrapment inside circulation/filtration system, check or re-makeup pretreatment chemical (e.g. cleaner) and monitor organic contamination from time to time (e.g. TOC analysis).

Regards,
David

A. Hi Yogesh. We appended your question to one of several threads about pitting in acid copper plating. David has just answered, but your situation is not clear to me, so please clarify it --

You say you get pitting in the high current density area even when you plate at low current. In other words the pitting occurs only at corners (where current density is highest), but the problem is actually unrelated to the current density?

Have you plated any Hull Cell panels? Do you know your chloride content? Do we understand your parts to be plastic? Thanks.

Regards,