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June 2016

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Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Wed, 8 Jun 2016 14:48:35 +0000
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I especially agree with Dave on the use of the Galvanic Table. It is really a chart only to show the range of dissimilarity, but that does not necessarily mean the greater the difference, the greater probability of a major electrical issue or corrosion issue. Other factors come into play, including environment, current, voltage, amount of metal, etc.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Hillman
Sent: Wednesday, June 08, 2016 9:27 AM
To: [log in to unmask]
Subject: Re: [TN] ENIG Board Finish with Tin Plated hardware

Hi team! I am a bit late on the conversation but I wanted to echo George's comments. Too many folks use the Galvanic Table as a set of absolute rules which it is not. The Galvanic table should not be ignored but the influence of the equipment housing/chassis is completely missing from the standard galvanic table compatibility discussion. Many folks have mechanical hardware in contact with ENIG or Immersion silver board surface finishes that would appear to be a severe problem but the interaction with the product use environment and/or the anode-to-cathode ratio is such that no problem will be realized. I would not change to Immersion tin for the reasons already mentioned by the TechNet community.

Dave Hillman
Rockwell Collins
[log in to unmask]

On Sun, May 29, 2016 at 10:31 PM, George Wenger <[log in to unmask]>
wrote:

> Michael,
>
> I agree with Tan Geok Ang. I fully understand why your mfg/assy 
> facility in EU is balking at the finish mismatch. However, I do not 
> agree at all with their suggestion that you change the board finish to immersion tin.
> Immersion tin surface finish has serious shelf life and solderability 
> issues and I know that sometime after you switch to immersion tin 
> you'll be wishing you hadn't switched
>
> Although Guideline #7 in "The TIN Commandments" published by AMP 
> indicates "Mating tin coated contacts to gold coated contacts is not 
> recommended.", before I would switch your board surface finish I would 
> ask your customer if they have ever seen any issues with your boards 
> related to finish mismatch. Since this finish mismatch is only used 
> for mechanical mounting I don't think the finish mismatch will cause 
> functional issues. Especially since you indicated you been using this 
> finish mismatch for some time and if that is the case I assume someone 
> would have seen a problem if there was one Also, there isn't much gold 
> on ENIG surface finish (only a couple of
> micro-inches) and there probably won't be any considerable amount of 
> corrosion
>
> If my mfg/assy facility told me I had to board surface finishes I 
> would push back really hard and tell them that if they are worried 
> about the gold/tin finish mismatch they should just take a soldering 
> iron and a piece of solder and "tin" the few ENIG pads on the board 
> where the hardware is mounted (i.e,, wet the ENIG pads solder which 
> will dissolve the small amount of gold and eliminate the finish mismatch).
>
>
>
> Regards,
>
> George Michael Wenger
>
> George M. Wenger
> Failure Signature & Characterization Lab LLC
> 609 Cokesbury Road, High Bridge, NJ 08829
> (908) 638-8771 (Home) (732)-309-8964 (Cell) [log in to unmask]
>
> ----- Original Message -----
>
> From: "Tan Geok Ang" <[log in to unmask]>
> To: [log in to unmask]
> Sent: Sunday, May 29, 2016 10:44:50 PM
> Subject: Re: [TN] ENIG Board Finish with Tin Plated hardware
>
> In long term , ENIG with Sn will cause fretting corrosion. BUT don't 
> change the ENIG board finish to Tin surface finish as it creates hell 
> lots of other issue during manufacturing.
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Yuan-chia Joyce 
> Koo
> Sent: Friday, 27 May 2016 11:43 PM
> To: [log in to unmask]
> Subject: Re: [TN] ENIG Board Finish with Tin Plated hardware
>
> > "We've built all these assemblies, many, many times without issue."
> you means Siemens didn't have the dissimilar metal coupling check?
> Build is not an issue, corrosion in the field and resistance change 
> might be... it is reliability issue. if your stuff only work on one 
> shot deal (like bomb), and you just engage the two parts upon short 
> usage life, not much of issue, if you are in the field for long time
> - like more than 3 month, you should consider dissimilar metal 
> coupling from the start of design phase - use some good material/ 
> process engineer to select mating parts properly (according to standards).
> better not be one of those electrical switches... not smart one either...
> jk
> On May 27, 2016, at 10:43 AM, Kuczynski, Michael wrote:
>
> > We've been using ENIG finish for our PCB's and installing tin plated 
> > hardware (self clinching, broaching nuts and standoffs)
> >
> > We use anywhere from 1 or 2 pieces, to maybe a dozen, of this 
> > hardware on various assemblies.
> > These items are used just to hold or mount some items in place (no 
> > serious stress on these items).
> >
> > Our mfg/assy facility in EU is balking at the finish mismatch and 
> > suggesting we change the board finish to immersion tin (which we've 
> > never used).
> >
> > We've built all these assemblies, many, many times without issue.
> >
> > Is there any other merits I should consider, before I tell them 
> > please build them as is?
> >
> >
> > Michael Kuczynski
> > Mgr. ECADS - Electrical 511 Benedict Ave.
> > 914-524-3118 (Ph) Tarrytown, NY 10591
> > 914-524-3322 (Fax) Mail Stop P25-1-C 
> > [log in to unmask]<mailto:[log in to unmask]>
> >
> >
> >
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