Thanks Dave I hadn't seen that data before 

----- Original Message -----

From: "David Hillman" <[log in to unmask]> 
To: "TechNet E-Mail Forum" <[log in to unmask]>, "George Wenger" <[log in to unmask]> 
Sent: Monday, November 21, 2016 11:51:06 AM 
Subject: Re: [TN] Immersion Tin - problems 

Hi George - Rockwell Collins/Celestica did some copper dissolution work with the SAC305 alloy as part of the NASA DoD project. For a temperature of 260C, the dissolution rate of a QFP pad was 0.043 mils/second. With that rate, I can dissolve a 2.5 mil thick copper pad in about 60 seconds. We published the data at the 2013 SMTA ICSR in Toronto. 

Dave Hillman 
Rockwell Collins 
[log in to unmask] 

On Mon, Nov 21, 2016 at 10:24 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