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October 2009

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Subject:
From:
Gabriela <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Gabriela <[log in to unmask]>
Date:
Wed, 28 Oct 2009 19:16:13 +0200
Content-Type:
text/plain
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text/plain (188 lines)
Well, taking the subject of the letters 'mot a mot', I can give you an
example of "real" birth of solder balls.
HASL coated boards with defective tenting (due to artwork or workmanship)
can contain excess of solder in the via holes- not blown out by the air
during HASL.
If you reflow the first side , the solder extrudes on the opposite side
through the small opening of the tenting and it really looks as if the via
gave birth to the small solder ball.
These small balls may stay in place or can be removed depending of the
surface they decided to stay. 
Printing the second side with such babies causes shorts on fine pitch
components , not so much because of the balls, as because the paste excess-
the stencil is not flat on the board.
Real Nightmare.
Want some pictures?
Gaby
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Wednesday, October 28, 2009 6:15 PM
To: [log in to unmask]
Subject: Re: [TN] Birth of a Solderball

Hi Leland -  you would need to use analytical techniques for 
micro-elemental analysis such as Scanning Transmission electron microscopy 
or Atomic Force microscopy and there is no guarantee that the resulting 
data would provide a source root cause (plus these techniques are big 
bucks). Some of the other recommendations from the TechNet crew are much 
more practical.

Dave



"Leland Woodall" <[log in to unmask]> 
10/28/2009 09:05 AM

To
"TechNet E-Mail Forum" <[log in to unmask]>, <[log in to unmask]>
cc

Subject
RE: [TN] Birth of a Solderball






Hi Dave,

Just how many thousands of dollars would that cost, and to what kind of
testing do you refer?

And I really didn't want to perform a cross section as well, so that was
good news!

Leland

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Wednesday, October 28, 2009 8:50 AM
To: [log in to unmask]
Subject: Re: [TN] Birth of a Solderball

Hi Leland - It may come as a surprise to many engineers but many metal 
alloys actually have a "DNA" which can be traced back to original 
processes and/or original sources. Unfortunately, unless you can find an

elemental signature difference in the solder alloy you use in your wave 
solder process versus your reflow process (which you will need something

more sophisticated that standard SEM assessment) you will not be able to

determine which process may have produced the solder ball. I don't
believe 
that cross-sectional analysis will be beneficial unless you have some 
baseline for comparison.

Dave Hillman
Rockwell Collins
[log in to unmask]




Leland Woodall <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
10/28/2009 06:54 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Leland Woodall <[log in to unmask]>


To
[log in to unmask]
cc

Subject
[TN] Birth of a Solderball






TechNetters,

Is there any possible way to determine the origin of a solder ball?
We've had a failure because of one, and we're trying to determine
whether it came from our SMT or wave soldering process.

We use SAC305 at both, so using the SEM to determine alloy composition
is not really helping.

The ball itself is spherical with no "tails" and quite shiny in
appearance.

If we cross section the ball, will we see a difference in grain
structure due to the differences in cool down rates?  Is there anything
else we can use or do?

Thanks in advance for your help!

Leland

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