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September 2006

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Subject:
From:
Mike Fenner <[log in to unmask]>
Reply To:
Date:
Mon, 4 Sep 2006 14:34:37 +0100
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Because the stand off is lower?  At low gaps surface tension can impede
flush though.


Regards

Mike


-----Original Message-----
From: Ingemar Hernefjord (KC/EMW) [mailto:[log in to unmask]]
Sent: Monday, September 04, 2006 10:29 AM
To: [log in to unmask]; [log in to unmask]
Subject: RE: [TN] PbCO3


Triple Hmmm!

I used Gilette, which is little rough, but it works fine: dropped a
board in LN2. When at -196 knocked the backside of the board, and the
CBGA jumped off. Could then study the cleanliness. No flux residues or
whatsoever.
Yepp, Vigon is indeed very active, but why does the phenomenon appear
only on CBGAs? We have other BGAs on the board, and these have never
shown such growths.

I'm attempted to go on quite another track for a while. One guy proposed
whisker growth. And, when you look at the SEM image, you find something
looking like pressing toothpaste out of its tube: whiskers? The guy (who
was it?) meant that CBGAs build up mechanical stress unlike other
components, and hence create whiskers.

Lead whiskers? Quadruple Hmmm. The litterature is very thin about Lead
whiskers,  not to say nearly non-existent. A few cases are reported, but
not regarding any BGAs, as far as I know. However, I will study the few
samples I got (am not allowed to touch the sharp boards)and see if it
can be Lead whiskers, or other type of Lead crystals. According to Sod's
law, I may be the one to be haunted by Lead whiskers...

Inge


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: den 4 september 2006 09:38
To: [log in to unmask]
Subject: Re: [TN] PbCO3

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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