Hi Richard!

I know one goal is to have zero voids. But is seeing them really a problem?

This all came about when I've been looking at upgrading our current x-ray
system. To be honest, I haven't seen voids here using our current equipment.

I've seen them now with some images from a sample that I've gotten with a
system that has more capability than our current system has. I asked about the
voids to the applications engineer, and was told that the voids that he observed
were normal, and not to worry about them, with the caveat that if they should
become larger, or more concentrated in any one area. He told me that he has
about 25-years experience working with x-ray inspection...so
I'm not that quick to go out and shoot him. He didn't say not to worry about
voids, but the voids that he observed from the sample I sent him were not a
concern...he said they were normal.

It seems that Werner agrees...

From the differing opinions, it seems the jury is still out about what is
still acceptable, and what really is rejectable when it comes to voids.

Right now, the J-STD-001 and -610 call out that more than 25% of the area of
the solder sphere is rejectable...it does not specify where they are located.

Anymore thoughts? Anyone?

-Steve Gregory-

***************************************************************

>Hi Steve,

>Seeing voids is indeed normal.
>What you are referring to is in IPC-7095, Section 7.5.1.6 Process Control
>Criteria for Voids in Solder Balls.
>This was a suggested process control example, and is NOT a requirement, nor
>was it meant to be one--otherwise, I would have voted negative on the
document.
>Putting it like your customer did is absurd.

>Werner

Voids can be caused by a number of things, but the most common cause is
the moisture content of the solder paste, and its condition.
That being said, a certain paste that has been known to be the mainstay
for many years currently is the worst one today as far as voiding. A
different paste manufacturer made an excellent paste that was formulated
to prevent voiding.
I recently performed a paste evaluation of standard 63/37, a leadfree
water soluble, and a leadfree no clean paste. There were 27 different
tests, with 5 vendors. On the standard 63/37, the paste formulated to
prevent voiding had ZERO voids in 1330 BGA joints, multiplied by 15
samples. The previous paste vendor had voids in every single BGA joint.
All variables were strictly controlled, and I did not know which sample
was being tested (they were numbered by someone else to prevent any
bias).
While I do not want to give out vendor names on the forum, I would be
glad to share this info with anyone offline.
The application engineer who told you not to worry about voids should be
taken outside and shot. While some data exists that says voids are OK if
they are small enough, you should certainly strive for an alloy that
provides you with an excellent grain structure free of voiding, with
evidence of good IMF at the pad/ball interface. Sorry, pal, but you
cannot determine this with an X-ray machine. It can only be done with a
good microsectional analysis.


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stephen Gregory
Sent: Monday, July 18, 2005 1:07 PM
To: [log in to unmask]
Subject: [TN] BGA voids

Good Day Technetters!

I have a question about BGA voids. We are bidding on some work and it
looks like they have taken statements that are in the IPC-7095, and
placed them as notes on their drawing.

One of the notes has to do with a limit on the percentage of balls on a
BGA device that are allowed to have voids. For example; "Less than 5% of
the balls can have voids, and the percentage of the void area must meet
class
3 requirements."

I can understand the void area being critical, but the percentage of the
number of balls that are allowed to exhibit them?

The reason that I'm asking, is that I was told last week by a
application engineer from a x-ray machine company (who shall remain
nameless), that seeing voids is normal. Just as long as they aren't too
big, or being concentrated at either the pad/ball interface, or the
ball/device interface.
He said you should worry if you don't see any voids on BGA's with
eutectic balls.

Just curious as to what you all think about this?

Kind regards,

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

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