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topic 5519

"Dot Skip" Problem in Decorative Chrome Plating of ABS Plastic




(2000)

Q. Hey friends, Am working with an automotive company in India (down south at Chennai). Been trying to develop decorative Chrome plating on some ABS (natural - plating grade) with a Supplier. Been having a couple of problems on the process with getting the perfect finish.

The problem is that we get some small (up to 2 mm dia.) dots of skip plating (we call it "dot skip") on the A surface (appearance face). It happens on almost all parts in the jig and hi rejection on this. They have got a bath of capacity of 10 parts (300 grams each approx. weight) with a 35 step process including all the swills and washes. But not able to fix the problem.

We guess it must be something to do with the etching process at the beginning stage of process, but not much works on getting this fixed. Anybody with ideas or prior experience or suggestions?

Urgent requirement to solve this issue - so please get to me fast. Thanks, Babu. R

Babu R
- Chennai, Tamil Nadu, India.


(2000)

A. If the small skips appear only on the outer surface it is probably caused by "chrome mist". The chrome mist in the air comes from the conditioner or from the decorative chromium solution. The mist is in the air and when it comes in contact with the parts that come out of the palladium bath, it causes a small dot. The brownish colour of the palladium disappears as a result of the chrome in the air and this dot cannot be plated with electroless nickel.

sara michaeli
sara michaeli signature 
Sara Michaeli
chemical process supplier
Tel-Aviv, Israel



(2000)

A. Dear Mr Babu,

A dot - skip plating has to be seen or explained more fully in order to pin point the source. You have to be able to determine it this is a pitting problem or skip plating.

From what I have heard, your spec calls for a high thickness of Copper and also a high thickness of Nickel plating , both processes which are pit prone.

In addition to Chrome mist, also look out for HCl mist, and ensure perfect degreasing before the Chrome etch right at the very beginning, because if an Air bubble sticks on to the plastic on account of Oil on the component surface or in the etch bath. regards,

Khozem Vahaanwala
Khozem Vahaanwala
Saify Ind supporting advertiser
Bangalore, Karnataka, India

saify logo


Plating on Plastics
Don Baudrand & Gurd Mueller

(2000)

Q. Hello,

Got your feedback - thanks for the information. I need to check it out with my Platers and awaiting their response. But couple of queries...

  1. Will the Decorative Chrome batch generate the Chrome mist? And which conditioner you refer to? Can this be avoided or reduced to maximum extent?
  2. How to control the Chrome mist - would separators work (screening the Pd bath from the rest or screening the Chrome bath from the rest)?
  3. Or could you suggest some absorbent or adsorbent agent for the chrome mist?
  4. Have you encountered this problem and what means you took to solve this?

Thanks for your prompt response and looking forward to more information ASAP.

Babu. R (returning)
- Chennai, Tamil Nadu, India.


(2000)

? Are you saying that when the problem occurs on a jig, almost all the parts on the jig are bad, and other jigs come out without the problem?

pooky
tom pullizi signature
Tom Pullizzi
Falls Township, Pennsylvania


(2000)

A. Conditioner is the chromic acid plus sulfuric acid solution. How to avoid chrome mist, well you can use in the decorative and in the conditioner a wetter that creates a foam layer. Ask your suppliers for it. It has to be a special wetter that is not decomposed by the strong oxidizing power of the chromic acid. To begin with you can even use polypropylene balls but they are not effective enough. ...also close the windows as the wind will increase the effect of the chrome mist.

Sara Michaeli
Sara Michaeli signature 
Sara Michaeli
chemical process supplier
Tel-Aviv, Israel



Standards and Guidelines for Electroplated Plastics

(2000)

Q. Dear Mr. Pullizzi,

From the observation, I cannot attribute to jigging because some components do come out well. It happens on all the jigs being processed and not concentrated on one jig.

I have been suggested to check out for 'Chrome mist' or some other mist particles which affect the part before the E-Ni. Could it be that bubbles settling on part during these stages leads to spots not getting activated? Thanks, Babu. R

Mr. Vahanwala,

Thanks for your response. Will be looking into it. We have been clear that it is 'skip' plating because the virgin plastic skin is visible on this area (dots of max 2 mm).

Felt that air bubbles may not be an issue as the chrome etch tank is constantly agitated and air bubbles get removed. Thanks, Babu.

Babu. R (returning)
- Chennai, Tamil Nadu, India.


(2000)

A. The etching solution is agitated and the air bubbles get removed as you mention but each bubble takes a little chromium into the air... think about it. Other things that may cause skips are: Too high Chrome plus 3 in the conditioner (over 30 g/l); too low pH in the EN; Not enough time in the accelerator (or too weak accelerator); Too short dipping time in rinses (mainly after Pd and after accelerator).

But none of these can explain why your skips are only in the outside and not in the inside of the parts. The only strong explanation to the one sided skips is the chrome mist.

Sara Michaeli
Sara Michaeli signature 
Sara Michaeli
chemical process supplier
Tel-Aviv, Israel



(2000)

A. Babu
My first thoughts are that you are getting chrome mist blowing off your etch tank or bright chrome tank onto the surface of the work after the neutralizer tank.Could there be any cross drafts from open doors etc that could blow the mists in that direction. (you may be able to check this by setting up a sheet of white paper, leaving it there for the day and checking for orange chromic spots). Secondly, do you have mechanical agitation in the activator,accelerator and electroless tanks? If there are any concerns about bubbles forming on the surface of the product causing skip, mechanical agitation will shake the loose. Is there any chance that oil form the likes of a compressed air supply could be sprayed onto the work, this could cause skip. Finally in the moulding process are the molders using any silicone based mould release agents, not necessarily on the machine that is manufacturing your components but maybe somewhere in the process they are getting overspray form another machine. (silicone mould releases are a not to be used for products to be electroplated. I hope this is of some help. Whatever is causing the problem is either already on the product or is happening between the start of the line and the electroless tank. Regards Tim

Tim Strickland
- New Zealand


(2001)

A. Dear Mr. Babu:

All the suggestions that you have received are very nice.

I support the chrome-mist theory the most. Actually we are running an ABS plating plant in Delhi itself, so we keep on facing this thing very often. Well this problem may arise due to improper strength of activator also.

Well Mr. Babu have you ever tried to redo the electroless process on the defected pieces? I mean dip the pieces in the accelerator(HCl)again and leave the jig for 5 minutes and then dip that jig into the activator and redo the process of electroplating. I hope that the skip plating holes would get ok this time.. do tell me about this thing as earliest.

Thanx and regards,

Sandeep Jain
- Delhi,India



To minimize searching and offer multiple viewpoints, we've combined multiple threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.



Problem in ABS Plating: "Dot-skip" plating

+

Q. Dear sir,

We have started an ABS plating plant (Nickel, gold & chrome plating) one year back. Since we are new we are facing lots of problems with etching, Pd, and electroless nickel. We are plating onto writing instruments.

Problems such as :

1) Lots of dot skips.

2) If forcefully electroless nickel with excess chemicals lots of problems from copper.

3) Kindly let us know timing factor in etching tank since we cannot fix the same and face various types of finish from electroless nickel tank. ( Our ded maintained 48 °C). Chromic 350 - 450, Sulphuric Acid 250 -300, Trivalent 22 at present. At the time of process the temperature is maintained at 70 °C and timing to the job is approx 20 minutes. Any suggestion if required.

4) Our electroless nickel bath decomposes every day or two. (Any kind of stabilizer available to avoid the same?).

Materials used in electroless nickel are :

* Mixture of Nickel Sulphate (3 kgs) & Sodium Succinate (250 gms) plus 11 ltr of water which we call as A.

* Mixture of Sodium Hypophosphite (3.5 kgs) & Sodium Citrate (1.5 kgs) plus 11 ltr of water which we call as B.

* Lacquer Ammonia Acid.

* As far as required temperature in the bath, it is around 40 °C. We are not using Sulphuric Acid. We heat with the help of a heater water to water i.e. tank filled with water is heated & our EN tank is placed into water that is heated.

* Since our electroless nickel bath decomposes every day or two we prepare a quantity of bath (approx. 10 ltr water, 2 ltrs of A, 1 ltr of B & 1 ltr of liq. Ammonia as and when required we keep on adding proportionally til decomposes. Kindly give suggestion for the bath if needed.

5) To remove plating from rejected goods is a headache. We use nitric acid;suggest if any other process can be for the same.

Awaiting for an early reply. We appreciate your efforts towards trouble shooting looking forward to you web.

Thanks.

Mr. Sunil Jhaveri
PLATERS - Mumbai, Maharashtra, India


(2001)

A. Mr. Jahveri:

Could not understand all your questions completely, but it sounds as if you are trying to develop your own Plating On Plastic (POP) process. This has taken years and millions of dollars to chemical suppliers around the world. Why don't you approach a well recognized Co. I will only answer to question 4: thiourea is a known stabilizer of EN, it is also a poison and can kill reaction.

Guillermo Marrufo
Monterrey, NL, Mexico


(2001)

A. Plating on ABS is a complicated and delicate process and one should try to purchase the electroless solution from a supply house that can provide you with the right answers. Anyhow I will try to assist you:

1. Adhesion problems in POP processes are connected to the conditioner and skips are connected to the EN.
2. Your formula of the EN is not a balanced one, try to find a better formula in the Metal Finishing Guidebook. A balanced EN solution can work for months without decomposing.
3. The EN should operate at about 35 °C and the pH should be about 9-9.2.
4. If the EN is OK parts should be covered in about 20-30 seconds.
5. Rinses, they are very important. Prior to EN the parts should be in water for at least 60 sec.
6. Last but not least, the accelerator between the palladium and the EN should be at the right concentration and changed once a week.

Let me know how are you getting on.

Sara Michaeli
Sara Michaeli signature 
Sara Michaeli
chemical process supplier
Tel-Aviv, Israel



 

A. Dear Mr. Jhaveri,

As has been mentioned by many experts the ABS plating is a tricky process and you must approach reputed companies like Atotech, Enthone, etc. for the complete solutions to your problems. Until and unless complete process audit is done at your works it would be very difficult to suggest any single remedy.

Thanks,

G.S.SHARMA
- MUMBAI, India


January 2, 2010

Q. Respected Sir,
We are in POP for the last 6 months and plating jobs for MNCs. we also face the same problem of skip plating. as Mr Jain has suggested, we redo the process from activator and 40% time the job is good. Extra dosings in HCl neutralizer after etching, activator, EN plating has helped reduce this problem.
But I am also lost as to why this problem can occur. Chrome mist if it is a problem can be provided with forced ducting (venting) of etching / decorative chrome arrest this problem.
Be kind enough to help us out of this ASAP.thanks.

Prasanna Borkar
- PONDA- GOA, INDIA


January 7, 2010

Q. DEAR Mr. BABU,
I TRIED FORCED VENTILATION ON CHROME ETCHING SOLUTION, PLUS I TRIED TO ISOLATE THIS BY PUTTING A PARTITION. FURTHER MY COPPER TANK WAS CLOSE BY THE ACTIVATION TANK; THIS AREA WAS ALSO FORCED VENTILATED AND YOU KNOW WHAT, 90% OF MY SKIP PLATING PROBLEM GOT SOLVED.
BUT BECAUSE OF THIS FORCED VENTILATION MY CONSUMPTION OF ENP CHEMICALS, AMMONIA HAVE SHOT UP. WE ARE STILL WORKING OUT THE EXACT DOSING PATTERNS.
THANKS TO ALL FOR RESPONDING TO THIS PROBLEM.

prasanna borkar (returning)
- PONDA- GOA, INDIA



October 6, 2011 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hi,

I'm a process engineer for a new plating on plastics plant. We plate ABS parts of Copper-nickel-chrome process for Automotive industry. Currently, we are facing a problem with our plated parts. A defect called "White Dot" layer occurred after parts finished plated. We had done everything but still the defect can't resolve.

Please help.

Thanks.

Hun

Hun Shaf
plating shop engineer - Malaysia


October 7, 2011

A. Hi Hun,

If the "White Dot" didn't show up after nickel plating but appear after chrome plating, then possible causes are:

1. High chrome bath pH;
2. Low wetting agent;
3. Low chrome complexing agent;
4. Low chrome concentration;
5. Lead contamination;
6. Poor activation after nickel plating or parts dries prior to chrome plating.

Regards,
David

David Shiu
David Shiu
- Singapore



Coating the surface of the point opening on ABS plating

December 29, 2015

Q. Hi;
I have an important problem in ABS plating process. We are dealing with this problem for a long time: a large opening in the coating surface is observed, looks like a big bubble but we think no palladium is there.

For this reason we tried a lot of methods -- we made a new activation bath, chromium sulphuric bath, acceleration bath , electroless nickel bath ... but we were unable to reach a conclusion. We don't know where does it get this error. We do not have much ideas anymore. Thank you in advance for your help.

hasan ibek
chemist - izmir, turkey



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