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From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Thu, 10 Dec 2015 16:43:22 +0000
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Thanks Dave, I am not an expert in SEM or whether it sees one type of carbon (such as from charring) differently than another type of carbon, such as a component of something like flux or burnt FR-4.
But I agree with both you and Joyce. Further analysis would need to be performed to see what the root causes of the SEM readings are. Everything else is speculation. But speculation is fun if you are not responsible for it! ☺

From: David Hillman [mailto:[log in to unmask]]
Sent: Thursday, December 10, 2015 10:35 AM
To: Stadem, Richard D.
Subject: Re: [TN] What else it can be

Hi Richard - flux residue gives a healthy carbon peak in SEM too.

Dave

On Thu, Dec 10, 2015 at 10:16 AM, Stadem, Richard D. <[log in to unmask]<mailto:[log in to unmask]>> wrote:
If you look at the picture you can see a solder fine on the fourth or rightmost lead. A smaller one can be seen on the third lead from the left also, in the upper left corner of the termination. The two large balls in the second are likely voids, I cannot tell.
If smaller Pb-free solder fines or particles are suspended in tacky flux under the part, it would explain what the gray substance is (flux), as well as the oxide level and high Sn peak.
The C is carbon, not copper (Cu) and is simply indicative of charring.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf Of David Hillman
Sent: Thursday, December 10, 2015 7:45 AM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [TN] What else it can be

Hi Vlad - I agree with Joyce, the SEM signature looks like tin oxide suspended in an organic (note the C peak). I sometimes see this as SnOx in the flux residue after soldering.

Dave

On Wed, Dec 9, 2015 at 6:55 PM, Vladimir Igoshev <[log in to unmask]<mailto:[log in to unmask]>
> wrote:

> No underfill or any other fancy stuff
>
> ---- On Wed, 09 Dec 2015 16:53:28 -0800 Yuan-chia Joyce Koo<
> [log in to unmask]<mailto:[log in to unmask]>> wrote ----  > tin oxalyate used for epoxy
> catalyst... there were works for flux/  > underfill one step stuff
> utilize flux by product as catalyst for  > curing... (can't remember
> which group did that...)
>  >           jk
>  > On Dec 9, 2015, at 7:03 PM, Vladimir Igoshev wrote:
>  >
>  > > Hi Dave,
>  > >
>  > > Not really. It doesn't "burn" or "curl" much under the beam, so
> > > it's solid.
>  > >
>  > > Vladimir
>  > >
>  > > ---- On Wed, 09 Dec 2015 15:51:29 -0800 David  > >
> Hillman<[log in to unmask]<mailto:[log in to unmask]>> wrote ----  > >> Thank you
> Steve!
>  > >>
>  > >> Vlad - does the substance slightly charge in the SEM?
>  > >>
>  > >> Dave
>  > >>
>  > >> On Wed, Dec 9, 2015 at 5:46 PM, Steve Gregory
> <[log in to unmask]<mailto:[log in to unmask]>>  > >> wrote:
>  > >>
>  > >>> Hi Dave and Vlad,
>  > >>>
>  > >>> I have it up here:
>  > >>>
>  > >>> http://stevezeva.homestead.com/What_else_it_can_be.pdf
>  > >>>
>  > >>> Steve
>  > >>>
>  > >>> On Wed, Dec 9, 2015 at 4:34 PM, David Hillman <  > >>>
> [log in to unmask]<mailto:[log in to unmask]>> wrote:
>  > >>>
>  > >>>> HI Vlad - we can't open Dropbox here due to firewall  > >>>>
> restrictions so can  > >>>> you have Steve G. post the pictures?
>  > >>>>
>  > >>>> Dave Hillman
>  > >>>> Rockwell Collins
>  > >>>> [log in to unmask]<mailto:[log in to unmask]>  > >>>>  > >>>> On Wed, Dec
> 9, 2015 at 4:59 PM, Vladimir Igoshev <  > >>>>
> [log in to unmask]<mailto:[log in to unmask]>  > >>>>> wrote:
>  > >>>>
>  > >>>>> HI everyone,
>  > >>>>>
>  > >>>>> I'm attaching a link to a file showing something I'd
> appreciate  > >>>>> your  > >>>>> thoughts on. It's a cross-section of
> a QFN on an IAg board;  > >>>>> Pb-free/no-clean process. As you can
> see from the EDS spectrum,  > >>>>> that  > >>>>> greyish stuff
> between pins has pretty much only Sn and O in its  > >>>> elemental  >
> >>>>> composition.
>  > >>>>>
>  > >>>>> I know there is burn flux residue around solder joints but
> that  > >>>>> stuff  > >>>>> doesn't have any C in it. The question I
> have is what is it.
>  > >>>>>
>  > >>>>> I spoke to Bev and both of us are still puzzled.
>  > >>>>>
>  > >>>>> Here is the link:
>  > >>>>>
>  > >>>>
> https://www.dropbox.com/s/3wbj62vqjyhvj2y/What%20else%20it%20can%<https://www.dropbox.com/s/3wbj62vqjyhvj2y/What%20else%20it%20can%25>
>  > >>>> 20be.pdf?dl=0
>  > >>>>>
>  > >>>>> Thank you very much in advance.
>  > >>>>>
>  > >>>>> Regards,
>  > >>>>>
>  > >>>>> Vladimir
>  > >>>>>
>  > >>>>> SENTEC
>  > >>>>>
>  > >>>>>
>  > >>>>>
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