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May 2016

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From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Tue, 31 May 2016 11:42:56 +0000
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I totally agree with Tan's assessment. 
If there have been no issues over time, I would not change a thing. The one thing I would do is find serial number one of the series (or at least the oldest CCA you can get your hands on) and check for galvanic corrosion, but I doubt very much if you would find any.
The board house must have some other motive for wanting a surface finish change on the PWB. I suspect they do not know how to process ENIG properly (reflow profile issue).
The amount of gold on an ENIG finish is only around 4 microinches (not microns); I am not sure that can greatly contribute to any galvanic reaction. The nickel underneath certainly won't.
If a change does have to be made to the surface finish, immersion tin would be my last choice. It is horrible.
Odin

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tan Geok Ang
Sent: Sunday, May 29, 2016 9:45 PM
To: [log in to unmask]
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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