Hi folks! The "typical" solderball alloy for a CBGA is 90Pb - 10Sn which
keeps the CBGA from collapsing onto itself during reflow. Because the Sn
percentage is lower the usual tin oxidation reactions are not going to be
as dominating. I believe the reason Inge is observing only the reaction
exclusively on the CBGAs is the solderball alloy. The real question is
what is initiating the reaction!
Dave Hillman
Rockwell Collins
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Brian Ellis
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Sent by: TechNet To
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09/04/2006 04:53 Subject
AM Re: [TN] PbCO3
Please respond to
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Brian Ellis
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Just had a thought, Inge. Could your CBGA maker be conforming to RoHS,
by using high melting point balls with lots of lead, such as 99%?
Brian
Ingemar Hernefjord (KC/EMW) wrote:
> 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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