Hi Gerry

The issue is the potential for gold embrittlement in SMT solder paste
joints. The immersion gold over nickel self limits thickness at 5 to 8
microinches which when mixed with the relativly small amount of solder
paste used for SMT does not approach the approx 1-2% danger level.
Electrolytic deposits are typically 10 times thicker and can vary as
current densities are pattern sensitive.

If the board is through-hole and wave soldered, the washing action of the
wave will remove most of the gold to the solderpot and electo gold can be
used with less concern for embrittlement issues.




At 11:27 AM 8/6/98 -0400, you wrote:
>Hi George!
>
>We'll also be doing an application also requiring surface mount where a
>requirement for nickel-gold as a contact surface will exist.
>
>I was wondering why, since you were already body plating with
>electrolytic nickel, you didn't continue with body plating electrolytic
>gold?
>
>What were the issues that moved you towards using immersion gold instead
>of electrolytic?
>
>Thanks
>
>Gerry
>
>
>
>
>
>
>
> -----Original Message-----
>From:  George A. Anderson [mailto:[log in to unmask]]
>Sent:  Wednesday, August 05, 1998 6:03 PM
>To:    [log in to unmask]
>Subject:       Re: [TN] Electroless Nickel
>
>At 03:18 PM 7/31/98 -0400, you wrote:
>>I would think it wise to address the problem from a chemistry
>standpoint
>>or use an alternate surface finish before going the electroplated
>Nickel
>>route.  You will immediately either alienate or disqualify most of your
>>PCB suppliers.  Using electroplate requires surface continuity (unless
>>you're fortunate enough to have a design that is internally bussed,
>very
>>unlikely!)  so you're generally forced to do a body plate prior to
>>surface cu foil etch,  This most likely would entail the inclusion of
>an
>>electrolytic gold flash as well because the nickel would be difficult
>if
>>not impossible to re-activate if you were trying to utilize an
>immersion
>>gold process later on.  Not only will line definition suffer,  you run
>>the risk of  nickel slivers after etch, and lastly I doubt most profit
>>margins  will warrant the additional expense of body plated gold!!
>>
>We do run this process, i.e. body plated bright electrolytic nickel
>which
>serves as etch resist , then soldermask and immersion gold (Oromerse MN)
>on
>the exposed pads and thru-holes only. Applications are surface mount
>where
>a requirement for nickel-gold as a contact surface also exists,
>solderability is excellent, several passes OK. Activating the nickel
>just
>before gold is the key; we found a product called NiACT from Surface Tek
>to
>be effective and reliable.
>
>
>George Anderson
>President
>Uvonics Co. Inc.
>2162 McKinley Ave.
>Columbus, Ohio 43204            (614) 274-0040
><[log in to unmask]>           http://www.uvonics.com
>
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>
George Anderson
President
Uvonics Co. Inc.
2162 McKinley Ave.
Columbus, Ohio 43204            (614) 274-0040
<[log in to unmask]>           http://www.uvonics.com

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