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
>