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Subject:
From:
Don McFarland <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Don McFarland <[log in to unmask]>
Date:
Thu, 25 Aug 2011 08:56:16 -0600
Content-Type:
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Thats how it presented for us.

Don

----- Original Message -----
From: "Patrick Goodyear" <[log in to unmask]>
To: [log in to unmask]
Sent: Thursday, August 25, 2011 8:51:15 AM
Subject: Re: [TN] Removing SnCl2

Quick question for the ignorant.   

What is the visual representation of the SnCl residue, possibly a white stain?

Pat 

Dang Mike I did it again.    


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Thursday, August 25, 2011 2:37 AM
To: [log in to unmask]

Subject: Re: [TN] Removing SnCl2

Wow. You don't get this on Twitter!

:)
Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Thursday, August 25, 2011 1:19 AM
To: [log in to unmask]
Subject: Re: [TN] Removing SnCl2

Don,
I was interested in your question about tin chlorides and FTIR, so I did some digging.  As has been pointed out, SnCl4 itself is a liquid.  It is tetrahedral like methane and has four principle vibrations, all active in terms of Raman spectroscopy, but only two active in infrared spectroscopy.
The vibrations occur at 368, 106, 403 and 131 cm-1, with only the latter two being the ones active in IR.

SnCl4 reacts with water to form cis-[SnCl4(H2O)2]linked with other less tightly held water molecules.

SnCl6-2 is octahedral and again has four vibrations - three Raman active (314, 235 & 157) and only one IR active (313 cm-1).

So, it is a fair bet that all Sn-Cl vibrations occur at less than 500 cm-1.
If your spectrometer optics or the discs or cells you are using are made of NaCl, then the low frequency cutoff is about 650 cm-1 and you will never see any vibrations of bonds between atoms as massive as tin and chlorine.  Even with KBr optics the cutoff is around 400 cm-1, so you are going to still be out of luck.  

With regards to Raman Spectroscopy, the issue is whether there are multiple organic impurities mixed in with the inorganics that will result in enough fluorescence that your spectrum of any SnX species is swamped by the fluorescence signal.

Bev
RIM

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Don McFarland
Sent: Thursday, August 04, 2011 8:22 AM
To: [log in to unmask]
Subject: Re: [TN] Removing SnCl2

Sn(iv) would make more sense because this stuff seems impervious to anything we've thrown at it. 

We have traced it back and found that this residue is visually present on the bare ENIG pcb. We have the sem, edx ad ftir tests being done on the bare board to compare residual signature to post-assembly residues. The interesting this was our FTIR only showed FR-4, but nothing else. Should ftir detect these Sn residues if present and adequate sample captured? I am wondering if this is a laminate curing issue and not a contamination issue, since our data points arent seeing the chemistry.

The SEM/edx found minute flakes of Sn that appear to attach to Cu contaminate found on bare pcb. These embedded flakes are only visible at 1000x and are small at that...just a bit out of the allowed mag for fod inspection. 



Sent from my iPhone

On Aug 3, 2011, at 4:24 PM, R Sedlak <[log in to unmask]> wrote:

> Don:  I think I qualify as a "real Chemist", or at least I have a lot 
> of
people fooled...
> Actually, SnCl2 is easy to remove, but it is highly unlikely your 
> deposit
is SnCl2, but is much more likely to be SnCl4 (Stannic Chloride) which is rather more difficult to remove...
> I would recommend either a Caustic cleaner, preferably with some 
> chelate,
if your substrate can tolerate that.
> If not, probably the only other cleaner which will remove Stannic 
> Chloride
is a dip in an Ammonium Bifluoride solution, say, 5-10%.   Stannic salts are
highly insoluble, and hydrolyze easily to Stannic oxide, which needs either strong alkali, or HF to remove.
> Wish I had better news.
> Rudy Sedlak
> RD Chemical Company
> 
> --- On Wed, 8/3/11, Don McFarland <[log in to unmask]> wrote:
> 
> From: Don McFarland <[log in to unmask]>
> Subject: [TN] Removing SnCl2
> To: [log in to unmask]
> Date: Wednesday, August 3, 2011, 10:49 AM
> 
> Any ideas on methods to remove a tin chloride residue that was found 
> on a
FR-4 substrate after wave solder. We have done some good homework to find the source, but we are looking for good and proven methods to remove the residues from affected assemblies.
> 
> Any input is welcome. 
> 
> Regards,
> 
> Don McFarland
> 
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