From a pure chemistry standpoint, some of the newer immersion bath formulations have reducing agents that make them behave like electroless processing, and are not covered by the 455X IPC specs yet. IPC 4552A for ENIG (still in the works) calls them out specifically as ‘reduction-assisted’ immersion baths, rather than just plain immersion baths, to keep them separate. The purpose of calling them out separately is to highlight to the document user that these new formulations have not been vetted by the 4-14 committee yet, and are outside the scope of 4552/4556.
I’m not sure these reduction-assisted immersion chemistries are widely adopted or deployed in industry yet.
José (Joey) Ríos, Sr QA Engineer
Mission Assurance
Kavli Institute for Astrophysics & Space Research
Massachusetts Institute of Technology
[log in to unmask] <mailto:[log in to unmask]>
(617)324-6272
> On Nov 21, 2016, at 5:13 PM, George M. Wenger <[log in to unmask]> wrote:
>
> As usual Mr. Hillman gave a really knowledgeable answer and I agree with him totally. I've never pretended to be a chemist or fully understand plating processes but in simple terms what I've been taught to believe that a "True Immersion" plating process is a replacement process where when a metal component such as copper is put into and electrolyte with nobler metal ions, the less noble component or metal will undergo dissolution and this in turn results in the release of electrons, allowing the highly noble metal to settle down. In other words a "True immersion plating process" gabs a copper atom and replaces it with a more noble atom like tin (Sn) or silver (Ag). However, the immersion tin and immersion silver plating processes that are used in final finish plating on PCBs are "basternized" not "True" immersion processes in that they basically grab and replace copper atoms but they also have some "electroless" attributes allowing the plating process to continue increasing the thickness of the nobler metal.
>
> My original suggestion for a cross section was just to make sure that Jose's PCB shop was giving him PCBs with the proper copper and final plating finish that he specified. If he is getting the proper plating then he needs to control his soldering processes to insure they do not dissolve all of the copper plating.
>
>
> ----- Original Message -----
>
> From: "David Hillman" <[log in to unmask]>
> To: [log in to unmask]
> Sent: Monday, November 21, 2016 4:35:07 PM
> Subject: Re: [TN] Immersion Tin - problems
>
> Hi gang - great conversation but I think we need to get ourselves on the
> same page in terms of definitions. A true immersion plating process is, as
> Jose and George detailed, self limiting but the majority of the immersion
> plating processes today would be better described as electroless processes
> where a reducing agent is a component of the plating formulation which
> allows the deposition process to continue. Look at the IPC-4556
> specification, Appendix 1 (written by Martin Bayes) for a full explanation
> of the differences between an "immersion" and an "electroless or
> autocatalytic" plating system.
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
> On Mon, Nov 21, 2016 at 12:00 PM, Jose A Rios <[log in to unmask]> wrote:
>
>> Keep in mind that plating by 'Immersion’ is self limiting, once the copper
>> is coated by tin, the deposition rate tapers to where it no longer deposits
>> tin, I think that point is somewhere around the 30 uin mark.
>>
>>> On Nov 21, 2016, at 11:24 AM, George M. Wenger <[log in to unmask]>
>> wrote:
>>>
>>> Juliano,
>>>
>>> You suggestion would be to cross section one of the pads before anything
>> is soldered to the pad to see how much copper there is below the immersion
>> tin.
>>>
>>> The first step in the immersion tin plating process is to microetch the
>> copper (which removes some copper) and then during the immersion tin
>> plating more copper is removed and replaced with tin. The thicker the
>> immersion tin is applied the more copper is removed. So I think you need to
>> determine how much copper there is left so that when you go through the
>> soldering process you should be able to determine if there will be any
>> copper left after soldering.
>>>
>>> I haven't seen any specific dissolution rate info for Pb-Free solders
>> but I know the dissolution rate for copper into SnPb solder at 435F given
>> in an old Wally Bader paper is 4 u"/sec. so if your solder is molten for a
>> minute and a half you'll dissolve 360 microinches of copper.
>>>
>>> George
>>>
>>> ----- Original Message -----
>>>
>>> From: "Richard D. Stadem" <[log in to unmask]>
>>> To: [log in to unmask]
>>> Sent: Monday, November 21, 2016 8:47:54 AM
>>> Subject: Re: [TN] Immersion Tin - problems
>>>
>>> Thanks for your input Juliano.
>>> If others have also seen this, it would be interesting to see just how
>> widespread this issue is. IPC should have guidelines on what to do to
>> prevent it (ENIG finish, 1/2 oz copper minimum, etc).
>>> As I posted earlier, I have seen it happen many times at many client
>> companies, and I am simply trying to get the word out. Many have no idea
>> what may have happened, and be unfairly blaming the PWB fabricator.
>>> It is a process/design issue.
>>> dean
>>>
>>> -----Original Message-----
>>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Francesco Di Maio
>>> Sent: Friday, November 18, 2016 8:12 AM
>>> To: [log in to unmask]
>>> Subject: Re: [TN] Immersion Tin - problems
>>>
>>> Hello Juliano,
>>> I think you are facing a problem of copper dissolution as Mike wrote.
>>> This problem become more evidentemente with lead free solder alloy, also
>> it may be presente with Sn/Pb alloy.
>>> In our experience the use of Sn100 alloy may help to mitigate the effect
>> of the annullar ring partial or complete dissolution if compared to
>>> SAC305 or SAC405 alloy.
>>> We noted this problem during solder pot (solder fountain) rework used to
>> remove and resolder pth connector.
>>> The selective soldering with long contact time, higher solder
>> temperature, higher solder flow rate in my opinioni may cause the problem
>> you noted.
>>> Try to reduce these variables and problem should be mitigate.
>>> Preheating the assembly before or during the selective wave soldering,
>> may help.
>>>
>>> Regards
>>> Francesco Di Maio
>>> SEM Comunicazione & Gestlabs
>>>
>>>
>>> -------- Messaggio Inoltrato --------
>>> Oggetto: Re: [TN] RES: [TN] RES: [TN] Immersion Tin - problems
>>> Data: Thu, 17 Nov 2016 16:25:03 +0000
>>> Mittente: Mike Fenner <[log in to unmask]>
>>> Rispondi-a: TechNet E-Mail Forum <[log in to unmask]>, Mike Fenner
>>> <[log in to unmask]>
>>> A: [log in to unmask]
>>>
>>>
>>>
>>> There could be a number of reasons. I offer the following to add to your
>> list of things to investigate.
>>>
>>> The immersion tin will dissolve very rapidly into the Solder which will
>> then start to dissolve the Cu pad underneath to form a solder joint. If
>> your pads/tracks are small/thin then it is possible the Pb-free solder
>> could dissolve the pad entirely. Pb-free solders can be more aggressive in
>> this respect than Sn/Pb due to the higher tin content. The Sn is more
>> concentrated/less dilute compared to Sn/Pb. Processing temps are also
>> higher. The problem can be increase by a turbulent or fast wave.
>>> Reducing the exposure time may help.
>>> I suggest you might want to consider your Pb-free finish for unrelated
>> reasons. Immersion tin is a variable process and has a relatively short
>> storage life. It's hard to think of any advantages it has, save possibly
>> for cost.
>>>
>>> ---
>>>
>>>
>>> Regards
>>>
>>>
>>> Mike
>>> www.chrisfennerfund.org
>>> www.facebook.com/chrisfennerfund/
>>>
>>> -----Original Message-----
>>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Datacom - Juliano
>> Ribeiro
>>> Sent: Thursday, November 17, 2016 11:46 AM
>>> To: [log in to unmask]
>>> Subject: [TN] RES: [TN] RES: [TN] Immersion Tin - problems
>>>
>>> Many pads
>>>
>>> _____________________________
>>> Juliano Bettim Ribeiro
>>> DATACOM
>>> +55 (51) 8446-2135
>>> +55 (51) 3933-3000
>>> Ramal: 3484
>>>
>>>
>>> -----Mensagem original-----
>>> De: Stadem, Richard D. [mailto:[log in to unmask]] Enviada em:
>> sexta-feira, 11 de novembro de 2016 11:40
>>> Para: TechNet E-Mail Forum; Datacom - Juliano Ribeiro
>>> Assunto: RE: [TN] RES: [TN] Immersion Tin - problems
>>>
>>> One, or many?
>>>
>>> -----Original Message-----
>>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Datacom - Juliano
>> Ribeiro
>>> Sent: Friday, November 11, 2016 5:21 AM
>>> To: [log in to unmask]
>>> Subject: [TN] RES: [TN] Immersion Tin - problems
>>>
>>> Damaged = "Pad disappeared" the track has broken
>>>
>>> _____________________________
>>> Juliano Bettim Ribeiro
>>> DATACOM
>>> +55 (51) 8446-2135
>>> +55 (51) 3933-3000
>>> Ramal: 3484
>>>
>>>
>>>
>>> -----Mensagem original-----
>>> De: TechNet [mailto:[log in to unmask]] Em nome de George Wenger Enviada
>> em: quinta-feira, 10 de novembro de 2016 17:32
>>> Para: [log in to unmask]
>>> Assunto: Re: [TN] Immersion Tin - problems
>>>
>>> What do you mean by "damaged"? Do you mean solder doesn't wet the pad or
>> is there physical damage?
>>>
>>> Sent from my iPhone
>>>
>>>> On Nov 10, 2016, at 1:16 PM, Vladimir <[log in to unmask]>
>> wrote:
>>>>
>>>> Hi Juliano,
>>>>
>>>> The board finish most probably has nothing to do with the problem. It
>>>> must
>>> be your process.
>>>>
>>>> Regards,
>>>>
>>>> Vladimir
>>>> SENTEC
>>>>
>>>> Sent from my BlackBerry 10 smartphone on the Rogers network.
>>>> Original Message
>>>> From: Datacom - Juliano Ribeiro
>>>> Sent: Thursday, November 10, 2016 13:13
>>>> To: [log in to unmask]
>>>> Reply To: TechNet E-Mail Forum
>>>> Subject: [TN] Immersion Tin - problems
>>>>
>>>> Hello to all,
>>>>
>>>>
>>>>
>>>> We recently are changing to Lead Free process to specific products and
>>>> we need to change the finishes boards from (HAL Tin Lead) to Immersion
>>> Tin.
>>>>
>>>> But during the Selective Soldering process the component pad is damaged.
>>>>
>>>> Are there limitation about Immersion Tin about Max. Temperature, Max.
>>>> Reflow/Wave process, Max Soldering Contact Time, etc.???
>>>>
>>>> In this case the HAL Lead Free is better?
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> Thank you
>>>>
>>>> Juliano Ribeiro
>>
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