"Dot Skip" Problem in Plating of ABS Plastic

? Hi Vikram. We assume you're dealing with plating on plastic because that is where the term "skip plating" is predominantly used, so we attached your inquiry to a long thread with lots of instruction regarding what you can do next. But give us some details please. Thanks.

Luck & Regards,

A. Hi Vikram. We moved your question about contamination of Pd activator tank to thread 56574 rather than have this thread wander. While we await answers on that new one, please tell us what you did to resolve those skip plating issues. Thanks.

Luck & Regards,

A. Hello sir,
For skip plating problem solution I took some steps as below-
1) Reduce the temp. of etching ( 3-4 °C)(for instant result only)
2) changed water rinse and dragout after etching.
3) Strengthened neutraliser and pre dip( Make new if possible)
4) Slightly increase tin and Pd( ppm) in activator.
5) Keep focusing on etching chrome -- must not travel up to activator tank.

So these were the steps I took to resolve my skip plating problem.
These steps I took according to my understanding.

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.

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,

? 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?

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.

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.

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

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,

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 [on eBay or Amazon] is a known stabilizer of EN, it is also a poison and can kill reaction.

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.

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,

A. Skip plating of ABS can be due to many factors, including poor moulding, poor etching, poor rinsing, poor activation or poor electroless bath control. If the moulding is not done correctly, the surface can be depleted of butadiene and this will result in an inability to etch the surface and subsequent loss of plating nucleation sites. Similarly, if the surface is not adequately etched by the chromic acid, it will not plate. Even if the surface is etched properly but it is not rinsed properly, the chromic acid will kill any further processing, so good neutralisation and rinsing is essential. Once etched, the surface needs activating and if the palladium/tin is not working properly, no electroless metal deposition will take place. If the electroless bath is not in spec, you haven't got a remote chance of getting it to plate. From the brief description you have given I would suggest you are possibly suffering from inadequate rinsing, but the other possibilities above are still valid.

A. Hmmm...all kinds of reasons are possible.
But because you gave a good description of the problem area I think the most likely explanation can be found in the distribution of butadiene in the SAN matrix (styrene acrylo nitril). It are the butadiene spheres which get etched out leaving cavities behind for activation and adhesion of the metal layer.
Your metallisation process works well on other areas of the letters.
Maybe you should try a few tests with different molding conditions...less pressure, less hot plastic.
No, personally I would not make any changes in the metallization parameters...not my first choice to seek the answer in the plating...it works on other areas of the letters you plate.

Have fun.

Warmly,

A. You probably have a "scum" on the top of your etch solution. When you introduce the racks, it holds the scum in the "pockets" as it enters. (I bet this is the case.)
Either move your solution better, or program the equipment to go up and down as introduced to the etch.
Regards,

A. Dear Sir,

Skip plating is due to
1-degreasing is not perfect
2-reduction of chromium after Etching is not sufficient
3-activation time is not adequate or solution is out of balance
4-acceleration [time and solution]is not suitable use NaOH instead of HCl

Good luck,

A. Well, there are a lot of possibilities here.

When you say that there is no coverage, do you mean that there is no electroless nickel?

Chrome aerosol can cause this kind of skip plating. By skip I mean that there are spots with no plating at all.

I assume that you use a suitable wetting agent in the etcher to prevent aerosol problems. You can check whether you have aerosol problem by using big filter papers dipped in diphenyl carbazide solution. If you put a paper close to the EN solution and you get purple spots on it, it means that you have chrome in the air.

BUT, there are a lot of other possibilities :

How much trivalent chrome do you have in the etcher?

The rinse time prior to the EN should not be just a short dip. This rinse must rinse of SN+4.

And the most important -the quality of the water you use. The water for ALL stages, including rinses should be RO.

A viszontlatasra

Sara

A. Hi,

1. If you have a positive carbazide test, it means that the wetter you are using in the etch is not doing a good job. It is either an non adequate wetter or the amount is too low.

2. Trivalent chrome - I understand that this is a new solution. Trivalent in high quantities causes problems but if it is zero, it is a problem as well. You need a minimum of 3-5 g/l trivalent chrome in the etcher. Chromic acid concentration should be 420 g/l and sulfuric 170 cc/l = 313 g/l.

3. I don't know how big are your parts and what is the volume of your solutions. In order to evaluate whether the cause is a result of chrome mist, I would try to etch parts in the plating line,(only the etch, not the following rinses) and perform the post etch sequence in another room on lab scale, in small scale of course. This way you can eliminate the chrome mist and see whether your problem is solved.It is imperative to eliminate the chrome mist on lab or small scale in order to be sure that this is the root cause.

4. Water - you wrote that you have no RO water. I hope that all water used is DI including make up of ALL solutions and ALL rinses.

5. Facing up areas - Your remark regarding facing up areas is mostly correct. Is your problem mainly on facing up areas?

6. Mist suppressant is a wetter.

7. Forced ventilation is a must - first of all to ensure safe working area for the employees.

8. Are you sure you etch the parts properly? The ABS has a kind of glassier which make parts look bright. After the etching and rinsing, parts should look MAT or DULL.

9. Initiation - how long does it take (in seconds) since the parts are immersed in the EN till the reaction starts?

10. Last but not least - the molding. If the molding is not perfect, you will have spots. Are you familiar with the acetic acid [on eBay or Amazon] test to evaluate the quality of the ABS?

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

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Ed. note: I think a picture would be worth a thousand words, Andres.