You may want to re-read page 2: Copyright C 2005, Intel Corporation. All
rights reserved.
And after that take in and enjoy the whole presentation.
Enjoy the day.
Ahne.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Monday, October 17, 2005 11:05 AM
To: [log in to unmask]
Subject: Re: [TN] Voids in BGAs, again
Here's a link to a pretty good presentation about voids, I'm assuming it is
public information since I found it searching the internet:
http://www.smta.org/files/oregon_chapter_presentation0905.pdf
Kind regards,
-Steve Gregory-
Senior Process Engineer
LaBarge Incorporated
Tulsa, Oklahoma
(918) 459-2285
(918) 459-2350 FAX
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| | "Kane, Joseph E |
| | (US SSA)" |
| | <joseph.kane@BAES|
| | YSTEMS.COM> |
| | Sent by: TechNet |
| | <[log in to unmask]>|
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| | 10/17/2005 10:35 |
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| | Please respond to|
| | TechNet E-Mail |
| | Forum |
| | <[log in to unmask]>|
| | ; Please respond |
| | to "Kane, Joseph |
| | E (US SSA)" |
| | <joseph.kane@BAES|
| | YSTEMS.COM> |
| | |
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| To: [log in to unmask]@SMTP@Exchange
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| cc: (bcc: Stephen R Gregory/LABARGE)
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| Subject: Re: [TN] Voids in BGAs, again
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Some BGA connections with voids fail.
Some connections without voids also fail.
And some solder joints with void area of 50% of the connection cross-section
last just fine.
This was much debated in committees developing the new revisions of
J-STD-001 and IPC-A-610 (and from what I hear, in the IPC-7095 committee).
After many months of discussion, no one could point to any rigorous data
showing that voids in the bulk of the solder connection cause any problems.
That being said, most agree that voiding at the interface can be a bad
thing, and should be avoided.
But seeing holes on an x-ray image does not, in itself, mean that the thing
will crack.
If there is any data out there that anyone can share, it would be much
appreciated, that much I know for sure.
Joe Kane
BAE Systems
Johnson City, NY
-----Original Message-----
From: Stadem, Richard [mailto:[log in to unmask]]
Sent: Monday, October 17, 2005 10:16 AM
To: [log in to unmask]
Subject: Re: [TN] Voids in BGAs, again
Hi, Ioan
I have had the "opportunity" to see several failures due to voiding in
previous jobs where I worked on military products. One of the most memorable
was a circuit board that was part of a device that was launched; it was shot
out of a gun. To qualify the device, several were assembled, inspected,
tested, etc. very carefully. Upon the gunshot, the device failed. During
failure analysis several cracked solder joints were found on a particular
SMT 1208 capacitor which was used several times on the assembly. One of
these that actually caused the electrical failure came out of its solder
joint on one end and caused an open circuit condition. A very intensive
analysis was undertaken to find the reason why this particular capacitor
part number's solder joints and no other solder joints on the assembly
cracked. There were many other similar SMT chip caps and resistors, as well
as much larger components.
None displayed any stress related to the gunshot. The failed capacitor that
caused the open circuit was at a 45 degree angle with the board.
The anode was still soldered to the pad, but the cathode was up in the air,
fully out of the solder joint. The top half of the solder joint was still
soldered to the end cap, the remainder of the solder joint was still
soldered to the pad. While much analysis was being done, X-rays, SEM
analysis to determine impurities, XRF to determine robustness of the surface
finish, etc. and other attempts at root-cause determination, etc., a second
unit was built up and was gunshot. This time all of the processes had been
double-checked. Not only did the second assembly fail the same way, but the
same capacitor fully fractured on one end and caused the open circuit again,
in the same location on the assembly, and again it was sticking up in the
air exactly as it had done on the first assembly. Talk about perfect defect
replication! At this point I was called in to the factory to see if I could
determine what the problem was. Upon examining the X-rays of the two failed
assemblies, I noted two things. The first was that there was a small solder
void on every single one of the capacitor's set of solder joints, the second
was that it was always on the cathode end of the capacitor, never the anode.
When looking at the end cap's configuration I was puzzled, as both appeared
to be the same. So I assumed that some type of outgassing of the component
occurred on the end that was voiding. This was not the case, however. When I
was finally able to get some loose parts to examine, no outgassing was
observed up to 230 C. in a special chamber. After the outgassing test, I
looked for evidence of venting under a microscope.
What I found was a very small .015" hole on the bottom of the cathode
termination. This hole had been overlooked by those who had looked at the
parts before me, and I did not see it when working on the failed boards. It
was not shown or noted on the component print, as it was felt to be
"insignificant" by the component engineer. This hole provided a means of
trapping air and flux during assembly and was the cause of the voids seen
only on the cathode end. These voids were not large, perhaps between 15 and
25% of the flat area of the solder joint formed between the termination and
the pad. However, it was enough to cause a solder joint fracture, and
because this particular failing component was near the center of this board,
the board flex was higher than those near the edges. When the capacitor was
replaced with a different vendor that had no hole, the boards all passed
gunshot testing.
I have also seen voiding cause solder fractures on interposed pin
components. When examining solder joints that underwent thermal cycling,
those solder joints with voids were much more likely to develop cracks and
fail electrically than those that had no voiding. Fixing the voiding problem
by changing to a different solder paste and or a slightly longer time above
liquidus temperature (TALT) fixed the cracks.
In a previous job, BGAs that had failed in the field and were returned for
failure analysis were found to have voids in the failed ball(s). In nearly
every case, if the BGA failed at all, it was noted that voids were present.
When we looked at good units returned from the field for other problems,
such as a cracked flex circuit, no voids were seen when we examined the BGAs
or they were extremely small. This assembly did not see any abnormal
physical stresses, and its normal service environment was typically that of
a laptop computer, it was essentially a field computer for the military, so
it saw occasional instances of extreme heat and cold and some drop shock.
I know of several studies that have stated that voiding will help prevent a
crack from propagating completely through the solder joint as it provides a
stress relief mechanism, and several other papers that take an opposing
view. I am no Werner Engelmaier, but one thing I have noted is that
microsections of solder joints from assemblies where some of the solder
joints show voids typically have a much coarser grain structure than those
that do not, and in that case all of the surrounding solder joints also
display this coarser structure, even in the solder joints without voids.
Solder joints microsectioned from assemblies where a different solder paste
was used that was formulated to resist voiding, and a slightly longer TAL
during the reflow profile was used, produced a much tighter grain structure
and no voiding.
Whenever this was accomplished there were few, if any, fractures.
That much I know for sure.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan
Sent: Monday, October 17, 2005 8:03 AM
To: [log in to unmask]
Subject: [TN] Voids in BGAs, again
Hi Technos,
I know this has been debated at least once a month, but I will not ask what
is the acceptability.
What I want to know is if anybody had the ocasion to actually see failures
related to voiding. How did you realize they were due to voiding? Also, do
you have any dirty pictures of the issue?
Thanks,
Ioan
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