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July 2005

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Subject:
From:
Stephen Gregory <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Tue, 19 Jul 2005 12:51:43 -0500
Content-Type:
text/plain
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text/plain (164 lines)
Since I started this thing, I'll share the images that I was talking about.

When I first saw these, I was kind of suprised...and a little concerned. As
I
said earlier, I had never seen voiding like this with my present x-ray
system...
I really don't know if it's capable of resolution like the system has that
took
these images.

Anyway, when I did see the voids I asked the question if there was a
problem
with voids like this, and was told no. I was told that the voiding that is
in the images
are pretty typical, and really don't warrant any concern. In fact I was
told that the x-ray
images showed that BGA soldered very good.

You can see the images at; http://www.stevezeva.homestead.com   then click
on
Picture Page 2, and then look for Pre Void Calculation, and then Post Void
Calculation.

The system software calculated that the voids within that sphere were
5.3%...and that
sphere represented the worst one as far as voiding was concerned in that
BGA. Almost
all the spheres did have some voiding.

Kind regards,

-Steve Gregory-
Senior Process Engineer
LaBarge Incorporated
Tulsa, Oklahoma
(918) 459-2285
(918) 459-2350 FAX



|---------+---------------------------->
|         |           Vladimir Igoshev |
|         |           <[log in to unmask]
|         |           >                |
|         |           Sent by: TechNet |
|         |           <[log in to unmask]>|
|         |                            |
|         |                            |
|         |           07/19/2005 10:43 |
|         |           AM               |
|         |           Please respond to|
|         |           TechNet E-Mail   |
|         |           Forum; Please    |
|         |           respond to       |
|         |           Vladimir Igoshev |
|         |                            |
|---------+---------------------------->
  >--------------------------------------------------------------------------------------------------------------|
  |                                                                                                              |
  |       To:       [log in to unmask]                                                                              |
  |       cc:                                                                                                    |
  |       Subject:  Re: [TN] BGA voids                                                                           |
  >--------------------------------------------------------------------------------------------------------------|




Hi Werner,

That is exactly the point I wanted to make. Every time a crack "coalesce"
with a void, it would have to re-nucleate again and it's not an easy thing
to do.
There is one sentence in your e-mail I'd be very cautious about. Some
people (and a very limited number of them) they do report the presence of
voids at the interface and for some strange reasons call them Kirkendall
voids. As far as I know, it have not been any data published, which would
show that the presence of those voids were due to the difference in the
diffusion rate in between 2 different materials. So, I wouldn't call them
Kirkendall voids, just now. :-)


Regards,

Vladimir
Vladimir Igoshev, Ph. D.
Senior Materials Researcher
Research in Motion
451 Phillip St.
Waterloo, ON, N2L 3X2

Voice: (+1) 519-888-7465, ext. 5283
Fax: (+1) 519-886-0863
E-mail: [log in to unmask]

-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Tuesday, July 19, 2005 11:33 AM
To: Vladimir Igoshev; [log in to unmask]
Subject: Re: [TN] BGA voids


Hi Vladimir,
You are correct.
I have never seen an overstress failure of a solder joint that involved
voids in the solder joint bulk volume. I have seen creep-fatigue failures
in SJs with voids that did not involve the voids at all, or that went
through the voids, but were not caused by them. I have even seen SJs with
cracks in them where the cracks stopped at a void.
Overstress failures invariably involve the interfaces of solder joints
where for a variety of reasons really weak 'links' were created; that
includes interfacial failures due to Kirkendall voids.

Regards,
Werner Engelmaier





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