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
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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://ddei3-0-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2fwww.multicircuits.com%2fassets%2fcontent%2ffiles%2fimmersion%5fsilver.pdf&umid=705E821A-9491-C705-8178-F5BB3192C729&auth=a79cf964896a44925c32628edeb2301b3739bcef-b1871a82e596801861e5b27331309139ba19ca10
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
* * * * * * * * CONFIDENTIALITY NOTICE * * * * * * * *
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 disclosure may be unlawful. If you are not a named addressee, you must not use, disclose, retain or reproduce all or any part of the information contained in this e-mail or any attachments If you have received this transmission in error, please destroy it and notify us immediately by return e-mail or by calling + 1 888 208 9005.
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