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September 2006

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Subject:
From:
Mike Fenner <[log in to unmask]>
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Date:
Mon, 4 Sep 2006 08:38:11 +0100
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Double Hmmmm!

Applying Occam's Razor to this. Put everything you have done to one side for
a moment and just imagine you were at the early stages of investigating this
problem.
You would describe a situation where you are using a reputable resin based
flux and then clean them in a reputable semi-aqueous cleaner. Everywhere is
OK, except under a large component.
My immediate thought would be that you are not cleaning under the component
as well as you think or at least are not washing/rinsing out the cleaner.
Vigon is a very high pH material and therefore chemically active.
How do you know you have cleaned under the device? Are you lifting it off to
do something like ROSE?  If there is a flush though problem then ROSE will
not detect it.
My apologies for pointing out what is basic stuff like this to someone with
your knowledge/experience, but sometimes it is easy to overlook something
when it is too simple.


Regards

Mike



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hfjord
Sent: Sunday, September 03, 2006 10:19 AM
To: [log in to unmask]
Subject: Re: [TN] PbCO3

Hmmm....

I have excluded residues that stem from reactions with the solder mask and
other reactions from solvents and fluxes. The reason is, that such residues
appear immediately after the soldering process, while our residues GROW
slowly during weeks and months. And only on CBGAs. Furthermore, we have
investigated the space between the CBGAs and the board, and it's absolutely
clean, because we use a very effective and powerful Vigon 200 washing
machine.
So, it is still a mystery.

Inge



----- Original Message -----
From: "Mike Fenner" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, August 31, 2006 4:20 PM
Subject: Re: [TN] PbCO3


>I can puzzle out how you could get carbonate but not how you would get lead
> carbonate. Lead is unreactive compared to other metals present and they
> would react in favour of the lead, or even if the lead reacted would
> displace it in the corrosion cell reaction.
> If you are getting significant carbonate formed so quickly then this would
> imply a fairly high acidity on the work, which is hard to relate to that
> found in electronic grade fluxes.
>
> You have nothing to lose by trying an activated rosin base flux to reduce
> this stuff -whatever it is - and floating it away as a slag/dross in the
> rosin, but I doubt it would be effective unless you re-melted the solder.
> If
> you were to do that it would be similar to some purification processes for
> solders [and other metals,]
>
>
> Regards
>
> Mike Fenner
> Indium Corporation
>
> T: + 44 1908 580 400
> M: + 44 7810 526 317
> F: + 44 1908 580 411
> E: [log in to unmask]
> W: www.indium.com
> Pb-free: www.Pb-Free.com
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Ingemar Hernefjord
> (KC/EMW)
> Sent: Thursday, August 31, 2006 9:21 AM
> To: [log in to unmask]
> Subject: [TN] PbCO3
>
>
> We got lots of such growth on CBGA balls recently. After
> soldering/cleaning: nada. After one week in stock: signs of growth.
> After one month: unacceptable crystals. Now, being insoluble in water
> and many solvents, some specialists advise you to mix an RA with
> ethanol, heat this mixture and dip the part until the crystals vanish.
> My question to TN is whether there is alternative methods? Some accept
> PbCO3 growth as being harmless, but this is not our intention, because
> loose particles are semiconducting and can create leakage current paths.
>
> Brian's book "Cleaning and Contamination of Electronics and Assemblies"
> mention there are five groups of white residues, but, oddly enough, lead
> carbonate is not included. The chemistry world of soldering residues is
> so complicated, that I have to ask you for help.
>
> Thanks in advance
> Ingemar Hernefjord
> Ericsson Microwave Systems
>
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Messages sent via this medium may be subject to delays, non-delivery and unauthorized alteration. This email has been prepared using information believed by the author to be reliable and accurate, but Indium Corporation makes no warranty as to accuracy or completeness. In particular, Indium Corporation does not accept responsibility for changes made to this email after it was sent. Any opinions or recommendations expressed herein are solely those of the author. They may be subject to change without notice.***

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