Cecilia,
Could be,
From my paranoid time working in military hybrids, I would
recommend storing as many things as possible in dry Nitrogen. How old are
the parts? are they stored in dry air (with a dessicant), or just in a "box
on a shelf", if allowed to react with damp air, I guess its conceivable
that the flux has undergone some form of reaction (maybe the flux supplier
could comment (any one from Kester listening?)
I dont know if it would make much difference, but could you try plasma
or microblast cleaning the CBGA balls and trying the reflow agin? or just
use a different batch of CBGS? If none of these are available, you could
always try the nasty Nitric-Acetic mix, although I dont recommend this for
production it would suggest if there was something amiss with the solder
balls on the CBGA Just make sure you get all the solution off to ensure it
does not cloud the results. If that seems to do the trick, see about
getting the BGA's reballed
Keep trying, youll get there eventually
Roger
___________________________ ReplySeparator____________________________
Subject: RE: [TN] BGA solder residues
Author: "Cecilia Alkhagen (EMW)" <[log in to unmask]> at
#email
Date: 27/08/99 13:42
Hello,
I am working with Ingemar on this problem with the BGA:s.
Could it be that the problem has occured because the solder bumps on the
ceramic BGA were heavily oxidised and that the solder paste flux had a low
reactivity (of some reason)? The flux may have dissolved some oxides and
then we are left with lead ions in solution beneath the BGA.
Should CBGA:s be kept in inert atomsphere? Today we only store plastic
components in nitrogen atmosphere we might suggest that CBGA also should be
stord in a similar way
Cecilia Alkhagen
******************************************
Ericsson Microwave Systems AB
Production Engineering Development
Bergfotsgatan 2
S-431 84 Mölndal
Telephone +46 31 747 0000
Direct +46 31 747 0288
Fax +46 31 747 2635
-----Original Message-----
From: Roger Massey-G14195 [mailto:[log in to unmask]]
Sent: Wednesday, August 25, 1999 5:05 PM
To: [log in to unmask]
Subject: Re: [TN] BGA solder residues
Ingemar,
I would not recommend washing the parts in your solution, just to
get the line going again.
Although the Nitric/Acetic mix does remove your vegetables (back to
cooking in electronics?), just think about what its doing, its
obviously dissolving out the Pb in the deposit, so think about what
its doing to the solder balls, and any other joints that its coming
into contact with. This stuff eats Cu and Ni etc, and probably does
nasty things to soldermask too.
Long term, and probably short term reliability would be suspect to
say the least, and I would think I could hear the MIL people scream
from over here.
On trying to locate the source of the stuff, What is the history
of this device and build layup, is the component etc new to you, or
have you "been using it for years?" if you made this stack before,
does this run use a new or different batch of the FR4, BGA etc?,
it may be limited to a bad batch of something, and a quick change in
product batch may help. Alternatively, have any parts been sitting out
in stores for a couple of months? could be they have absorbed some
nasties from the environment?
I would love to see a picture of your growth, I need a new
wallpaper for windows anyway and crystals tend to look funky, so
please zap it over.
Meanwhile, look on the bright side, if you get rid of this stuff,
you could suggest to management that you have just completed a
succesfull Pb reduction exercise, I understand is a kinda hot subject
in some areas of industry??
Keep us all informed as to what the tests get back
Roger
______________________________ Reply Separator _________________________________
Subject: Re: [TN] BGA solder residues
Author: [log in to unmask] at #email
Date: 25/08/99 15:40
Will try that reflowing, Roger, good idea,
will also try XPS for chemical determination. Roger, I tried to cook the
cabbage in the following solution: 1part HNO3, 4parts glacial acetic acid, 10
parts H2O. The result was surprising. One dip 2 seconds in the solution (room
temperature) and then rinsing in tap water and all crystals were gone! If we
are desperados, do you think we dare to perform handcleaning the boards that
way in order to avoid production stop? (The man with the saucers may have
something to say, we are also making airborne electronics. Any bad feelings
about the idea? Will the MIL people scream?)
This did not tell why the crystals grow, that's still the headache, maybe your
proposals will give something.
If you want a photo of the cabbage, I can mail such a one to you, Roger. Or
anyone else who is interested.
See you /
Ingemar
> Ingemar,
>
> Have you tried "reflowing" the individual parts and seeing if they
> bloom on their own? If your lucky, it could be due to a suspect single
> component type if unlucky its a compound reaction from interactions.
> (could be some gunk leaching out of ceramic etc Dont know about PbCO3
> but try something like an XPS analysis, which should more or less tell
> you how the stuff is bonded together and in what relative
> concentrations.
>
> Roger
> Motorola AIEG
>
>
> ______________________________ Reply Separator
_________________________________
>
> Subject: [TN] BGA solder residues
> Author: "TechNet E-Mail Forum." <[log in to unmask]> at #email
> Date: 25/08/99 12:29
>
>
> Oumphf!
> You can't pronounce that? Like me not being able to see what strange
> roses we find between the balls after BGA on FR4 after 10 minutes in a
> REHM heat conveyour oven. Top temp is +230 / 1 minute. Preheat is
> included in the 10 minutes. Kester 229D is used (if a Kester man reads
> this, please give a line or two in response. The residues grow to
> something that reminds of roses or cabbage! Colour in daylight is white,
> but the residues do not seem to belong to the ordinary white residues
> (Tin Abiate, polymerized rosin and lead salts). Flakes are <<1micron
> thick and up to 50microns in diameter. EDAX gives 99%Lead and bal is some
> Tin and Carbon and other random elements. Not soluble in the usual
> solvents like Ethylene, Perclorethylene, Acetone etc. And that is
> natural, as the residues are inorganic. Kester 229D is not QPL'd. Paste
> Sn62Pb36Ag2 is screenprinted on traditional Cu/Ni/Sn-pads. We have used
> this Kester formula for years for other products without seeing cabbage
> nor roses. BGA is ceramic C4 from Mota, number of balls (bumps) approx.
> 25x25 matrix.
>
> Can it be PbCO3? The flux is RMA and contains clorides.
>
> The line is stopped, nothing will be delivered until the cabbage growth
> is eliminated. Special question to SIRguru labs: can we send this job to
> you if our qualification does not cover the need?
>
> Regards
> Ingemar Hernefjord
> Ericsson Microwave Systems
>
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