Dennis, Wayne and David,
Many thanks for the update of definition.  Really dated myself and  
eye opening. All I know with some sort of immersion Ag, is the Ag  
doped OSP for easy optical vision system.  That is somewhat thicker  
compare to the old monolayer immersion Ag, and definitely, behave  
differently during reflow (depend upon how large your process window  
is, of course).  The OSP version decomposed early, and Ag immersion  
type oxidized somewhat prior to reflow if you do not have nitrogen  
oven.  The electroless type of "immersion" I would expect different  
somewhat too... Good to know. Many thanks again.  (definitely  
wouldn't do a equivalent type and swap it on the flight using same  
reflow profile... unless you have large margin - at least I wouldn't  
dare).
Best regards,
                       joyce
On Aug 11, 2015, at 5:26 PM, David Hillman wrote:

> Hi gang - Wayne, you are faster than I but I can add some additional
> detail. In Appendix A of the IPC-4552 specification, there are the
> definitions of "electroless" and "immersion" which mirror Wayne's  
> details
> but with more words. The definitions were added to the specification
> because Joyce's question is very common.
>
> Dave
>
> On Tue, Aug 11, 2015 at 4:15 PM, Wayne Thayer  
> <[log in to unmask]> wrote:
>
>> 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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