I know of a few cases where over-exposure to X-rays has damaged certain
components, most often CMOS components. Some CMOS EEPROM components can
even be damaged by overexposure to UV light.
It is not very likely, but it is definitely quite possible. It has
happened, and it is a concern.
If you are looking at a particular area on a pwa, the adjacent areas are
also being exposed. If you continue to go back and look at that area,
the total accumulated dose can hurt certain CMOS components (and other
types as well).
It is not very likely, but there are steps you can take to prevent
inadvertent damage from overexposure. 
Again, read Tom Clifford's article on the subject.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phillip Bavaro
Sent: Tuesday, September 27, 2005 1:17 PM
To: [log in to unmask]
Subject: Re: [TN] X-ray inspection, can it damage devices?

Hi Steve,

I haven't ever heard of or experienced any issues with an xray
inspection system causing damage to a chip.    It is hard to believe
that xrays momentarily exposed to a chip could cause damage.

I have seen some Altera BGAs that have difficulty getting good solder
joint reflow due to the heatsinks on top of them, the pwb's 24 layers,
and the sheer number of solderballs (1500+).  With your .050" copper
core, I would look at the thermal reflow and make sure that all the
balls on the BGAs have fully collapsed.

Was this BGA on the second side or first side reflowed?

It is tough sometimes to tell where the problem is if you don't have a
board level test in place.

Phil


Steve Gregory <[log in to unmask]> wrote:
Good Mornin' Everyone!

I hope you all had a good weekend! I worked Saturday, but had Sunday
off. Sat around Sunday and watched the NASCAR race at the "Monster Mile"
in Dover Delaware. 20-year old Kyle Busch gave Jimmie Johnson a run for
his money finishing second at the green/white/checkered ending....but I
digress.....

Anyways, we built an assembly here that has a .050" copper core in the
center of it...not the same assembly as the one I did my "okie
cross-section" on).

It is double-sided SMT, and has BGA's on both sides. I'm doing x-ray
inspection with a Fein Focus Tiger 160, and in order to penetrate the
core and do a proper inspection of the solder joints and spheres of the
BGA's, the x-ray power is up around 120-130kv.

Our customer received a number of the assemblies from us (without test
from us, as they are prototypes and test hasn't been developed yet), and
they are having problems with one of the BGA's.

It's a 100-ball Max-7000 device from Altera, a CMOS EEPROM, and our
customer has been trying to program the device via on-board programming,
but some boards wont program. The x-ray inspection turned out fine. All
BGA's were inspected using oblique angles, so if there was an open
joint, it would have been seen.

They are worried that maybe the x-rays may have damaged the device.
Altera has told our customer that the x-rays shouldn't hurt the device.
I've got
a case number started via email in to Altera (since I can't talk to
anyone on the phone), asking them myself if x-rays will damage the
device. I'm also going to call Fein Focus and talk to them as well.

But have any of you ever heard of x-ray damaging BGA's?

Kind regards,

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