TECHNET Archives

August 2015

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Tony Lentz <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Tony Lentz <[log in to unmask]>
Date:
Wed, 12 Aug 2015 12:18:08 +0000
Content-Type:
text/plain
Parts/Attachments:
text/plain (116 lines)
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
>>>
>>
>>
>> _____________________________________________________________________
>> _
>> This email has been scanned by the Symantec Email Security.cloud 
>> service.
>> For more information please contact helpdesk at x2960 or 
>> [log in to unmask] 
>> _____________________________________________________________________
>> _
>>
>
>
> ______________________________________________________________________
> This email has been scanned by the Symantec Email Security.cloud 
> service.
> For more information please contact helpdesk at x2960 or 
> [log in to unmask] 
> ______________________________________________________________________


______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

ATOM RSS1 RSS2