Letter 37073

Black and White Spots on Tin Plating on Brass C2600 1/2H  

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Dear Platers/ Professionals,

I have a long-time pressing matter over the issue of "Black Spots & White Spots" after the raw material Brass-C2600 (Temper: 1/2H) is plated with Tin.

Additional notes:
Thickness of raw material: 0.25mm & Width: 57 mm


After our formal meeting with our plater, we were told by them that the spots could be due to:

(i) storage conditions has to be in cool condition to avoid spots from surfacing (prefer air-con).

(ii) porosity of raw materials that causes the spots to protrude out of the plated layer

Are the above reasonings sound to you all?

Need some of your guidance in these issues.

Appreciate if you could send me an email on this or reply in this forum

Thank you for considering this thread and thanx in advance for submitting your solutions.

Yours Sincerely,

Alan Chow (QA)
Hoshin Kenzi (Metal Slitting) - Singapore

Hi!

If those spots came visible after a certan period (two weeks and more) and not just after plating, they maight been "produced" by a Zn from a brass, that is diffunding through Tin... We call this "Tin plague" .
This can (and must) be avoided with a 1 or 2 micron thick layer of Copper (better is Nickel) ower the brass. Then you can plate this parts normal with Tin....

Best regards!

Dimitrij Us
- Kranj, Slovenija (EU)

Hi Dimitrij,

Thanks for your reply and answer.

Really apreciate your help.

Have not been following up this thread for quite some time, just happen to find it on the search engine on this topic which I rmbr posting quite sometime back.

Now the same supplier is giving me coils that are having problems like black dirts and black spots on the topside of most coils. After cleaning using DI water , its even worse.

In fact, all these plated coils come with Ni under-coat over the Brass, C2600-1/2H.

Based on the platers' Cert of Conformance (COC) reports: Nickel (Ni) coating is maximum of 39.37u" (=1 um), the results states 0.65um to 0.8um.
and
Tin (Sn) is min of 78.74u" (= 2 um), results states 2.5um and above.


I am not sure how these black spots can erupt on the coils.
Can Dimitrij and plating profesionals out here advise and enlighten me on this issue?

Thanks a million.... Alan

Alan Chow
Hoshin Kenzi (S) Pte Ltd - Singapore

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