Couldn't agree more! My observations, exactly. In a nutshell; what you see is what you get.
-----Original Message-----
From: TechNet <[log in to unmask]> On Behalf Of David Hillman
Sent: Friday, October 11, 2019 7:38 AM
To: [log in to unmask]
Subject: Re: [TN] [External] Re: [TN] Tarnishing/Corrosion Associated with ESD Matt
Hi Rich - Collins has been using immersion silver for over 15 years and we do see tarnish from time to time. The tarnish is more a factor of variation in the plating process than your assembly process. In fact, I think the process of immersion silver tarnishing is a good thing as it give you an indication of how the finish is changing with relation to its assembly environment exposure and the overall quality of finish itself. Immersion silver will progress thru a visual tarnish color progression - yellow to gold to light brown to dark brown to black - as it get exposed to storage/processes and slowly degrades in terms of solderability. As for your ESD mats, as you and Rich detailed, there is sulfur in everything so if the tarnish was root caused to the ESD mats, you should be getting tarnish all the time and not sporadically. We asked the question long ago " what impact does the tarnish have" and in most cases, its a cosmetic issue that the human eye doesn't like. Unless the tarnish you are seeing has a functional impact, I would push back as tarnish is a characteristic associated with immersion silver finishes. There is no standard sulfur test that folks run on immersion silver finishes - most folks use the conditioning methodologies listed in the JSTD-003 to evaluate the finish.
Dave Hillman
Collins Aerospace
[log in to unmask]
On Thu, Oct 10, 2019 at 3:38 PM Richard Kraszewski < [log in to unmask]> wrote:
> Geeze really good stuff Rich and many thanks.
>
> I may likely come back to you with further questions as I dig deeper
> into this dilemma of mine.
>
> Rich Kraszewski
> Senior Staff Process Engineer
>
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> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D
> Sent: Thursday, October 10, 2019 12:32 PM
> To: [log in to unmask]
> Subject: Re: [TN] Tarnishing/Corrosion Associated with ESD Matt
>
> [EXTERNAL] This email was sent from outside of Plexus. Use caution
> when opening attachments or links from unknown senders.
> .
> I have had to qualify IAg handling/storage/processing procedures
> several times for various companies, and as part of that I performed
> testing for exposure to sulphides for the customer's particular IAg PWBs.
> I used a number of qualification methods, including the
> IPC-TM-650-2.4.4.4 steam aging process to a 5-year level, exposure to
> Sulphur-based clay/moisture method, and validated these with SIR
> testing after exposure, as well as performing all kinds of
> solderability testing after exposure as well. It is also important to
> qualify the finish against resistance to breakdown of your cleaning
> process. It is critical to never let wash/rinse water to evaporate
> from IAg CCAs, but perform a thorough blowoff and short bake after washing.
>
> What I discovered is that there are certain immersion silver plating
> PRODUCTS that provide superior resistance to tarnishing, superior
> resistance to creep corrosion, and superior wetting performance even
> if slightly tarnished. I also found there were some IAg plating
> products that were much inferior to others.
> I discovered that certain packaging processes definitely had a huge
> impact on the performance of the plating, sometimes not readily
> detected at receiving inspection, but definitely seen after reflow.
> Again, certain plating products proved superior in resistance to
> tarnishing and corrosion even if exposed to these handling and assembly processes.
>
> I know Dave Hillman can chime in and perhaps provide the TM-650 test
> method number for the clay exposure test, as I could not find that
> particular test method number in my files.
>
> The takeaway after all of that qualification is that once the
> handling/processing procedures were optimized, what is left is to
> identify which IAg plating products worked well, and which ones
> didn't. Then we shared this information with preferred PWB fabricators
> that we used, never mind any minor additional plating costs.
> Ever since, by sticking with only those "qualified" immersion silver
> plating products, and forbidding the use of others in our PWB
> purchasing specifications, we have seen very little issues with using IAg PWBs.
> I strongly believe the short-term exposure to vulcanized rubber ESD
> mats can cause some issues, but they are pretty much mitigated with
> the use of the better IAg plating products that use a co-application
> of tarnish-resistant binders.
> I am going to go ahead and name three that I am very happy with. One
> is Uyumera, another is McDermid's Sterling, and a third is OMG. Any of
> these are very good. I have no vested interest, just experience with
> all three that I do not mind sharing.
> I am particularly favorable to the Sterling product. It is very, very
> good. I especially like their extremely detailed Technical Data Sheet.
> It provides both a recipe for successful use, as well as a very
> specific process to audit the fabricator to.
> https://urldefense.proofpoint.com/v2/url?u=https-3A__ddei3-2D0-2Dctp.t
> rendmicro.com-3A443_wis_clicktime_v1_query-3Furl-3Dhttps-253a-252f-252
> fwww.multicircuits.com-252fassets-252fcontent-252ffiles-252fimmersion-
> 255fsilver.pdf-26umid-3D705E821A-2D9491-2DC705-2D8178-2DF5BB3192C729-2
> 6auth-3Da79cf964896a44925c32628edeb2301b3739bcef-2Db1871a82e596801861e
> 5b27331309139ba19ca10&d=DwIGaQ&c=ilBQI1lupc9Y65XwNblLtw&r=qMshjwqeixvQ
> js1qYTl8aRebuaqi25nLzYlpmDF6tjI&m=i3cbzkDSTHdTK9aQsAuckJs9olnvp1aGtRwT
> yUujpHk&s=-OsBpLWGlnW7g26zGBh4stLHTLM_uKVFWvzzXfYYstw&e=
>
> Just like solder paste, some brands and types lend themselves
> favorably to certain product use and assembly processes, some maybe
> not as good, but acceptable, while others you should just stay the
> hell away from if at all possible.
>
> Odin
>
> -----Original Message-----
> From: TechNet <[log in to unmask]> On Behalf Of Richard Kraszewski
> Sent: Thursday, October 10, 2019 10:25 AM
> To: [log in to unmask]
> Subject: [TN] Tarnishing/Corrosion Associated with ESD Matt
>
> Techies - I am being challenged to confirm or dispute a suggested
> correlation of vulcanized rubber ESD matts with some tarnishing and
> ("potential") creep corrosion we are seeing. Have tested the ESD matts
> with a classical sulfur "wet" spot test (Feigl) and have confirmed
> sulfide its presence in most matts which is not un expected.
>
> Issues we are having is sporadic and not at all consistent to all ImAg
> PCBs so I am sure (and aware) there are numerous other factors
> associated with this tarnishing/corrosion we are seeing.
>
> Does anyone have any experiences they can share, good studies or
> aware of any papers that may be of use in my quest?
>
> Is anyone of additional risk associated with any specific PCB ImAg
> plating process?
>
> Thanks in advance.
>
> Rich Kraszewski
> Senior Staff Process Engineer
>
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>
> This e-mail and any attachments are confidential from Plexus Corp. and
> may contain information which is privileged, confidential, and/or
> protected by non-disclosure agreements. They are intended solely for
> the use of the named addressee(s). . Any unauthorized use or
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> must not use, disclose, retain or reproduce all or any part of the
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