Customer says our tin plating has RoHS-incompatible lead. Where from?
A discussion started in 2007 but continuing through 2017(2007)
Q. We are a electroplating plant in Guadalajara, we currently Tin electroplate for the electronics industries. We need to supply Rohs compliant parts and one client has informed us that our parts have traces of Lead (ppm).
We have certificates by our suppliers that their products are lead free (and the rest of the RoHS prohibited substances) This are chromates, top coats, brighteners and Anodes.
What do you suggest we do? or Check ?
Our Anode supplier provides a certificate with lab analysis and according to this paper there is NO lead in the Tin Anodes, can this be accurate or our supplier is mistaken?
In this case, what type of Tin Anode do we need to purchase?
Thank you very much for your help
manager - Guadalajara, Mexico
A. There may be a number of reasons (some of them real and just, some not) for a customer to use the RoHS theme against you. Check for yourself Sergio. Hire a good level certified lab to check your plating. There must be good labs in your home town or in Mexico City. If your product passes but still they insist, get a second test from a reputable lab in their own country. If it doesn't, search the origin and do your job.
G. Marrufo-Monterrey, Mexico
Monterrey, NL, Mexico
First check that the incoming water to your process tanks is lead free (very old water pipes may be made of lead, newer old pipes have lead soldered joints if copper)If all your plumbing is plastic do not discount this source since water lines outside your building may be at fault.
You should also find out what method you customer used to "discover" the problem. Is it an approved method? Is the test being ran by someone properly trained?
Do you send out periodic samples to an outside lab or conduct any tests of your own? If not perhaps you should to see if you get the same result as your client before you begin a major investigation of your process
- great neck New York
Q. Guillermo and Gene
Thank you very much for your input. We haven't sent any samples to an outside lab, we have had difficulties finding a lab in Mexico that knows what we are talking about, we found some in the USA and the cost is around $500.00 USD for 1 part to be sampled.
But according to our suppliers there is no lead anywhere in our products. We are suspecting the Tin Anodes, even thou we have quality certificates, because the supplier said their Anodes are A type and we have heard there are AA and AAA for specifying the pure tin anodes, is this correct?
What kind of anodes shall we request. We haven't found in Mexico higher quality anodes.
Can Lead in the anodes be the culprit?
- Guadalajara, Mexico
A. The tin 'A' anodes may be the problem.
ASTM B339-00, 'Standard Specification for Pig Tin' lists three grades of tin. Compositions below, omitting elements other than tin & lead:
Grade 'A': 99.85% tin (min), 0.05% Pb (max).
Grade 'A' for the Manufacture of Tinplate: 99.85% Sn (min), 0.010 Pb (max).
Ultra Pure Grade: 99.95% Sn, 0.001% Pb (max).
Possibly, these ASTM grades correspond to the A, AA and AAA grades from your supplier; ask for certificates of analysis for each.
E51-67 (1978), 'Method for Spectrographic Analysis of Tin Alloys by the Powder Technique (Withdrawn 1984)' can be used for analysis [Probably, spark source atomic emission spectrometry since uses solid samples and is mentioned by NIST].
The US National Institute of Standards (NIST) sells 'Standard Reference Material (SRM) 1727 Anode Tin' with certified Pb content. SRM 1727 is a 30x30x30 mm cube of tin containing 33.26 ± 0.33 ppm Pb. Costs $601 but valid until 1/1/2028 expiration date. Small samples can be chipped off for spark source atomic emission spectrometry or dissolved in acid for other spectroscopy methods.
The first supplier below that I checked, Grant Mfg & Alloying, has 'Mamore' and 'Minsur' Grade "A" tin anode compositions with Pb contents well below 0.01%.
- Goleta, California
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Thanks for your answer, I'll contact the Tin supplier.
If we use electrolytic Tin anodes with 0.01% Lead, our parts will pass the RoHS test or do we need lower concentration in the anodes to comply with RoHS regarding Lead?
Do we need to have less lead in the anode to be able to pass the tests?
Thanks again for your help.
- Guadalajara, Mexico
A. From a recipe for 90Sn-10Pb plating (bath: 75 g/L Sn, 10 g/L Pb; anode: 90Sn-10Pb), tin may slightly preferentially plate. Starting with pure tin plating salts and a tin (0.01%Pb) anode, I'd expect the lead content of dissolved metals in the bath to reach about ~0.012% Pb, after which the composition plating out will match the anode. Thus, at steady state, the plating will contain ~0.01% Pb, well below the RoHS 0.1%Pb limit.
My tin plating experience is rather limited; experts please feel free to comment.
- Goleta, California
A. Ask for the LEAD REQUIREMENTS and the PROOFS that you customer had performed.
Otherwise Lead analysis can be performed with AAS or better with Electron Microprobe analysis.
- Minneapolis, MN, USA
A. Another thing to check is the material you are plating on.
Brass (And conform copper, copper that is formed from the billet cold instead of warm), contain a slight amount of lead on the surface.
This is normally deposited as the brass or copper is pushed from the billet through the die during manufacturing.
The lead is contained in a lubricant that used to help this process.
We discovered this to be a problem during our cleaning of brass in preparation for tin and silver plating.
The dry acid we used was causing a lead sulfate to form on the surface of the part causing bad adhesion.
We ended up using the dry acid with another chemical to bump up the fluoride in the solution.
Anyway, you can see that it may also be the copper that is not conforming to RoHS.
(P.S. our suppliers carried out an SEM scan for free, you should also try this if you do not take up Mr. Thompson's offer).
- Hythe, Kent, UK
A. As a manufacturer of the bulk of tin anodes in the US I thought I'd add my two cents. For 95% of the tin produced in the world, the lead content will range from 30 - 350 parts per million. This is approx. 99.95% pure tin. If you want high purity tin anodes (99.99% tin) you can get the lead down to around 15 ppm. That's the best you'll do for anodes. 99.999 tin (laboratory grade) is made with lead down to single digit ppm, but is not realistic from a cost or availability standpoint for electroplating in any decent quantity.
There should always be a lead value on your certificate of analysis for tin anodes.
- Coatesville, Pennsylvania
June 23, 2014
Q. Is Bright Tin Coated Brass per MIL-T-10727 ROHS compliant?
I am not sure where to ask this question but thought this might be an appropriate thread.
- Bloomingdale, Illinois, USA
A. Hi Richard. Probably not. There seems to be no requirement in that spec, which was cancelled long before RoHS was written, for coatings to be lead-free. In fact it warns repeatedly of the usual need for lead. Further, are you sure the brass itself is compliant (lead is frequently added to brass for machinability)?
Ted Mooney, P.E.
Pine Beach, New Jersey
October 15, 2017
Q. We have MSA-based 100% pure Tin plating line running without issues for several years. Suddenly the lead content went up to 1000 ppm in the bath, affecting the lead deposit on plated parts exceeding the 0.1% lead content max. The bath has Tin MSA, MSA, Additive and just DI water. What are the sources of lead in tin plating bath. We used 99.9% tin balls as anodes with max lead impurity of 100 ppm. Since lead will co-deposit on parts can it increase beyond 100 ppm in the plating bath solution.
Whether TIN MSA added to solution can have abnormal lead content. We faced severe oxidation of tin (stannous to Stannic) and bath became cloudy. Will tin oxidation in solution release any abnormal lead in solution? We noted heavy sludge formation in the tank for about 15% of the 1000 litres while taking up the bath solution for sulphuric acid treatment.
plating shop employee - Chennai, India
A. Hi Bala. We appended your inquiry to an earlier thread on the subject with lots of food for thought. Also, while I am not familiar with the "sulphuric acid treatment" of MSA baths, please note that contamination of sulphuric acid with lead is widely reported.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
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