shelf life and wirebondability, if you have high density device on board,
both are critical.  my 1.45 cents.  don't know anything about uyemura. 
never heard about it.
              jk
> Hi
>
> Could that relate to the Uyemura TWX-40? Supposedly a hybrid bath for
> plating thicker gold without damaging the nickel?
> It doesen't make sense for manufacturers to apply thicker gold electroless
> when they can use a simpler immersion process, why would anybody do that?
>
> BR
> Grunde
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
> Sent: 12. august 2015 13:02
> To: [log in to unmask]
> Subject: Re: [TN] immersion silver
>
> Very interesting addition to this discussion.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
> Sent: Tuesday, August 11, 2015 5:16 PM
> To: [log in to unmask]
> Subject: Re: [TN] immersion silver
>
> Hi Joyce-
>
> I thought perhaps someone smarter than me would give a carefully thought
> out response to your intelligent question, but it seems it was ignored, or
> went into my auto-junk machine, or maybe I've gone blind.
>
> Anyway, at some point in the 2000's the definition of "Immersion plating"
> got changed. I believe this happened because the immersion plating of your
> definition was extremely easy to use and care for. So people asked for
> "immersion" and the salesmen started claiming that finishes were
> "immersion"
> when they were actually "electroless" (which are a pain in the rear to
> apply, manage, and dispose of). I think Uyemura was the first to do this,
> advertising a thick "immersion gold". I remember going to their booth at
> IPC that year and trying to figure out what was going on, and when I did
> my impression was the salesman hid behind the "language barrier".
>
> So "immersion" now means any plating which uses no electrodes, and is put
> on "kind of" thin through careful process control.
>
> Wayne
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
> Sent: Tuesday, August 11, 2015 12:08 PM
> To: [log in to unmask]
> Subject: Re: [TN] immersion silver
>
> gurus, I need some education: Immersion process what I know of is surface
> ionic exchange process, once it covered surface, the chemistry stops, so
> it is a self limiting process.  What is thin and thick?  you means it can
> really gets thicker like electroless type?  not self limiting?  Many
> thanks.
> Best regards,
>                            jk
>> From memory the "thin" and "thick" silver finish classes recognised
>> that there were two competing but roughly equally popular IAg
>> chemistries in the industry , each with their own process max-min
>> deposit thicknesses and one typically thicker than the other.
>>
>> Clearly it didn't make sense for an IPC spec to have a "barn door"
>> range from minimum "thin" to maximum "thick", hence two ranges
>> defined. I don't recall one being "better" than the other because of
>> the thickness
>>
>
>
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