We've considered...

• the value (if any) of thicker immersion coatings
• the consequences (if any) of immersion-enriched solder joints.

I'll add that the more immersion coating we accumulate on the PCB at fabrication, the more we must fully absorb from the PCB at assembly. Failing that invites risk of components joined to some remnant amount of immersion coating.

Many may have seen fully wetted component joints that nonetheless pop-off revealing residual gold on the PCB terminals. While tin may variably absorb into the copper I wonder what would become of undissolved silver (and its influence on joint reliability).

Bob Lazzara

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Hillman
Sent: Tuesday, August 11, 2015 8:28 AM
To: [log in to unmask]
Subject: Re: [TN] immersion silver

Hi team - well, as usual the truth actually lies in the middle of the technical discussion. Supporting Vlad's point, solder is fairly robust to silver in terms of degrading integrity influences so in most of our soldering situations it's not an issue. Supporting Werner's point, he did have a specific case where silver embrittlement of the solder joint was the root cause of a series of solder joint failures. Werner and I had long discussions on that case as it was very interesting despite being somewhat of an odd case. So the final answer is silver can be an issue but it takes some specific metallurgical conditions. The immersion silver surface finished used today on printed circuit boards will not contribute to the degradation of solder joint integrity.

Dave

On Tue, Aug 11, 2015 at 7:02 AM, Vladimir Igoshev < [log in to unmask]> wrote:

> Hi Guy,
>
> With all due respect to Warner memory, silver IS NOT like gold and 
> DOES NOT cause embrittlement.
>
> Therefore, from the reliability point of view it wouldn't matter what 
> thickness of IAg was on a board, as long as we ONLY talking about the 
> amount of Ag which would and up in the joints after re-flow.
>
> Regards,
>
>  Vladimir
>
> Sent from my BlackBerry 10 smartphone on the Rogers network.
>   Original Message
> From: Guy Ramsey
> Sent: Tuesday, August 11, 2015 07:37
> To: [log in to unmask]
> Reply To: [log in to unmask]
> Subject: Re: [TN] immersion silver
>
> If Werner were alive he would be reminding us that silver, like gold, 
> is a contaminate in tin solder.
> Early finishes, prior to 2005 or so, weren't good for multiple reflows.
> Some
> presumed it was too thin.
> I believe the problem was the durability of the organic additives that 
> retard oxidation of the silver.
> Not perfect, but it is my preferred surface finish, but not too thick.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Kelly
> Sent: Monday, August 10, 2015 3:47 PM
> To: [log in to unmask]
> Subject: [TN] immersion silver
>
> Hi All,
> Why would someone choose thick immersion silver over thin? Are these 
> different chemistries? Regards Steve Kelly
>
>
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