I agree that it would be good to have words and terms and use of language to
have consistent, specific and precise meanings. Trouble is - people, us
basically.
People write specs for what they can buy, make and inspect for. Quite often
mixing everyday English into scientific terms and vice versa as they can be
working in areas on the edge of their knowledge zone.
Incoming specs will be written with supplier input and inevitably a little
marketing /self justification will creep in. Especially for new processes
/technologies. Later a consensus will emerge and eventually best practice
gets enshrined in IPC/ISO etc.
Much later we look back as now and try to puzzle out what it all meant,
looking for technical /engineering type logical explanations. Of course it
does help to know the history as knowing where we started helps explain how
it finished. But at this point I just recall what a colleague used to say to
me [often]: "Don't confuse things with logic".
So here we are looking back at the result of introducing two competing
technologies through the haze of time and residual marketing dazzle. What we
have in either case is an organic coating with added chemistry to co-deposit
silver. Irrespective of terms the chemistries are different and give
different thicknesses, but the important thing to users is do they work and
are there any functional differences to be aware of?
--
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ahne Oosterhof
Sent: Wednesday, August 12, 2015 7:27 PM
To: [log in to unmask]
Subject: Re: [TN] immersion silver
This discussion is a wonderful example of how communication problems come
about. If you do not have clear and concise meanings for words,
communication is going to become faulty.
Like using the word bovine when you are really discussing the price of a
cow. Or talking with someone about a cat. Do you mean a nice little house
cat or a tiger or could it be you are talking about a Caterpillar tractor?
To me, a non-chemist, when you are mentioning "immersion", I understand
dunking something in a liquid. What happens below the surface is really up
for grabs. Even "immersion plating" does not define well enough what is
going to happen.
So all of us need to know where these words for the various processes are
defined concisely and go from there. Someone might even add what the results
(and problems) are for these different processes.
Have fun,
Ahne.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Wednesday, August 12, 2015 5:41 AM
To: [log in to unmask]
Subject: Re: [TN] immersion silver
From experience, I can only state my observation of the Uyemura "Immersion
Silver" product. This will plate on ANY metallic surface and keep on plating
until you pull your piece out of the bath (when you let it go too long, it
looks coarse and brittle and can even flake off). I don't think the US FTC
is interested in mucking with industrial grade products, so "let the buyer
beware!"
When done properly, this product gives a great finish, despite the deceptive
naming.
Bottom line is you need to force the sales rep into a corner and demand to
know the differences (from a user perspective) between "immersion" and
"electroless". If they start switching languages or saying something
incomprehensible, or pretend not to understand the question, then you know
they just re-labeled the product to improve sales.
Wayne
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tony Lentz
Sent: Wednesday, August 12, 2015 8:18 AM
To: [log in to unmask]
Subject: Re: [TN] immersion silver
Hello Joyce,
I have been watching this discussion from the "wings" and have not seen any
specific comments on how immersion silver chemistry works. Here is some
general information about the immersion silver plating process and
chemistry.
Immersion processes are self-limiting in terms of thickness. There is a
certain maximum thickness of silver that can be plated within a reasonable
amount of time. Immersion plating processes are replacement reactions.
Copper from the pads is dissolved into the plating solution as silver metal
is plated. As the copper is covered with silver, the area of copper
available for further silver plating decreases. This reduces the plating
rate over time. At some point the plating reaction nearly stops because
the silver plating solution can no longer reach the underlying copper.
As a side note, electroless plating solutions contain both oxidizing and
reducing agents in the plating chemistry. Electroless plating solutions do
not dissolve the underlying metal of the pads. This means that electroless
plating solutions can continue to plate and build metal thickness at a
constant rate over time.
Best regards,
Tony Lentz
FCT Assembly
Field Application
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Yuan-chia Joyce Koo
Sent: Tuesday, August 11, 2015 5:40 PM
To: [log in to unmask]
Subject: Re: [TN] immersion silver
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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