Hi Joe! Your logic on the electrolytic gold is just backward - if the gold
gets too thick (e.g. greater than 30 uinches)  the resulting solder joint
will be embrittled to due the formation of a gold/tin intermetallic phase,
if you keep the gold thin (e.g. your 10-15 uinches) then you run the risk
of having solderability problems due to oxidation of the underlying nickel
plating due to poor gold plating coverage. The TechNet archives has a bunch
of info on this issue.  Hope this helps, Good luck.

Dave Hillman
Rockwell Collins
[log in to unmask]




                      Joe Layug
                      <[log in to unmask]        To:       [log in to unmask]
                      M>                       cc:
                      Sent by: Leadfree        Subject:  Re: [LF] LeadFree and Land Patterns
                      <[log in to unmask]
                      >


                      07/26/2004 09:32
                      PM
                      Please respond to
                      "(Leadfree
                      Electronics
                      Assembly Forum)";
                      Please respond to
                      Joe Layug







Hi John,

Thanks for quick reply.  Question now is, why do
companies choose 30 microinches thickness and not 15
microinches or 10 microinches.  Does anyone have a
paper on this one?

Regards,
Joe

--- John Burke <[log in to unmask]> wrote:
> Selective electroplated gold is used as a method to
> avoid black pad which
> can be an issue with ENIG. The effect in the BGA
> areas that arises sometimes
> with enig which is typically called black pad is
> actually associated with
> other failure mechanisms than classic black pad but
> either way, the
> electroplating avoids the issue.
>
> Kind regards,
>
> John Burke
>
> -----Original Message-----
> From: Leadfree [mailto:[log in to unmask]]On Behalf Of
> Joe Layug
> Sent: Monday, July 26, 2004 7:19 PM
> To: [log in to unmask]
> Subject: Re: [LF] LeadFree and Land Patterns
>
>
> Hi,
>
> I have a question on electroplated gold finish for
> PCB.
>
> 1.) Why is it that some companies require 30
> microinches electroplated gold all over?
> 2.) Why is it that some companies require 30
> microinches selective hard gold especially in BGA
> areas?
>
> My understanding is that if the gold plating is too
> thick, this would result in poor solderability.  I
> thought before that the 30 microinches hard gold is
> usually used for edge connectors.  Wouldn't it be
> cheaper for companies to use ENIG instead for the
> solderable areas?
>
>
>
> __________________________________
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