Hi Steve
Pls help to post a photograph of the stain on your site.
Thanks in advance for your support.
Tuyen Tran
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Friday, July 18, 2014 2:21 AM
To: Wenger, George M. [Contractor]
Cc: TechNet E-Mail Forum; Tuyen Tran
Subject: Re: Staining immersion silver coating on ground plane after assembling
Hi George!
Photo is here:
http://stevezeva.homestead.com/Immersion_Silver_Tarnish.pdf
Steve
On Thu, Jul 17, 2014 at 12:35 PM, Wenger, George M. [Contractor] <[log in to unmask]<mailto:[log in to unmask]>> wrote:
Hi Tran,
If I've read your TN post correctly it sounds like you have some PCBAs that have "stains" and are concerned about sending these to a customer. It also sounds like you didn't see the stains immediately after reflow but saw the stains on ground plane areas ten days after reflow.
If you look on line at the paper we presented at the SurFin 2000 Conference and read the four bullets on our title page you will see that we indicate silver does tarnish when exposed to pollutants.
* Silver Migrates !
* Silver Tarnishes !
* Silver Sulfides !
* So why would anyone use Immersion Silver?
Despite what one might think about the paper title immersion silver has been our surface finish of choice since 1996 and we've never had a product failure since then that was due to the immersion silver surface finish. I can't tell from your text just how "stained" the ground planes are but it might be helpful if you could forward a photograph of the stains to Steve Gregory and ask him to post it on his site. I've attached a photograph of a stained RF product PCBA to this email which you and Steve will see because you are on the email copy to but IPC TN will strip off the photo so others won't see it unless Steve posts it on his site. The photograph certainly shows a tarnished immersion silver surface finish. This PCBA was deployed in Asia in a non-controlled environment and it was subsequently exposed to a five day Battelle Level III MFG and then put back into a telecommunication system and operated properly. Yes the tarnish is a cosmetic issue but it should not have any detrimental effect on performance. One of the reasons we use immersion silver is because unlike copper, silver oxide and silver tarnish is conductive, which is the reason we believe we haven't seen any degradation of RF performance.
We were originally concerned that if we had tarnish the solderability might be degraded and we'd have problems soldering if we ever had to do subsequent component replacements or upgrades. This has not been the case. Our experience indicates that we can solder to almost any tarnished immersion silver surfaces. If the tarnish gets extremely severe (i.e., it turns totally BLACK) we have seen solderability degradation.
I can't give you a direct answer about shipping the product to your customer because I haven't seen how "stained" your PCBAs are and I don't know your customer. There are ways of removing tarnish on immersion silver, however, our experience indicates unless one is able to effectively clean or remove any of the chemically used to remove the tarnish that even though the cleaning process removed the tarnish it left harmful chemical residues behind that impacted the long term reliability of the product so we don't try to remove tarnish on immersion silver PCBAs.
You'll have to decide if you want to send your PCBAs to your customer. However, my suggestion is moving forward you should evaluate what caused the stains and see if you can prevent them. We've found some stains on reflowed PCBAs that were placed on mats on a work bench or laid on pieces of cardboard or other material that contained sulfur. We've also found stains on PCBAs that were handled by operators who were not wearing when the PCBAs were being handled. We even had a case of tarnish on immersion silver PCBAs that were on a wire rack next to a bench were an operator was peeling and eating hard boiled eggs.
The immersion silver PCBs we receive from various PCB fabricators are always separated with Silver Saver paper, we avoid handling immersion silver boards with bare hands, we specify what kinds of materials should not be used to package PCBAs and we minimize exposure of immersion silver PCBAs to the environment until they are delivered to customers.
Regards,
George
George M. Wenger
Failure Signature & Characterization Lab LLC
609 Cokesbury Road, High Bridge, NJ 08829
(908) 638-8771<tel:%28908%29%20638-8771> Home (732) 309-8964<tel:%28732%29%20309-8964> Mobile
E-mail [log in to unmask]<mailto:[log in to unmask]>
[log in to unmask]<mailto:[log in to unmask]>
-----Original Message-----
From: TechNet [mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf Of Tuyen Tran
Sent: Thursday, July 17, 2014 12:36 PM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [TN] Staining immersion silver coating on ground plane after assembling
Wayne
Yes, the staining on ground plane not affect 3F, because it were not soldered so it were stained during production time and looked so bad about cosmetic. Can you advise how to treat of stain? We not confident to delivery to customer these boards.
Thanks
Tuyen Tran
________________________________________
From: TechNet [[log in to unmask]<mailto:[log in to unmask]>] On Behalf Of Wayne Thayer [[log in to unmask]<mailto:[log in to unmask]>]
Sent: Thursday, July 17, 2014 10:57 PM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [TN] Staining immersion silver coating on ground plane after assembling
What's to solve?
Apparently the boards soldered OK, so it sounds like you are only talking about cosmetics. No long term reliability problem.
Talking with the PCB supplier about getting an anti-tarnish applied over the ImAg will help with the cosmetics.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf Of Tuyen Tran
Sent: Thursday, July 17, 2014 11:42 AM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: [TN] Staining immersion silver coating on ground plane after assembling
Hi Everyone
We received some PCBs where the finish surface was good, but after we ran reflow about ten days, the ground plane with immersion silver coating that were not covered by solder paste look to be stained on surface.
We known the chemical silver [Immersion Silver finish] surface is very sensitive to surrounding condition, it is easy to stain from oxygen/water vapour or production time exposure in the air.
We are looking for document on staining metal of the finished board. Has anyone else experienced something similar phenomenon or anyone have an idea to solve this?
Thanks
Tuyen Tran.
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