It sounds like you have been affected by the Mountain Dew.
Dewey

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Saturday, February 16, 2008 7:08 AM
To: [log in to unmask]
Subject: Re: [TN] X-Ray equipment

And here's why you can't see most solder joint cracks with x-ray:
Lead and tin are very good at stopping x-ray radiation. A BGA solder
ball or termination solder joint is relatively thick with respect to the
x-ray beam and a crack is usually perpendicular to the beam. In this
case a normal intensity beam is NOT going through the same thickness of
material irrespective of the presence of a crack or not. If you turn up
the beam current, you just white out everything. 

Now if you turn the sample so your beam is parallel to the crack you
might think you can see a hairline crack, but you still can't.  If you
are 5000 feet up a 10000 foot mouuntainn range you can't see through the
mountains even though there is air between each pair of peaks. Take a
complimentary-shaped mountain range and bring it down upside down so
that it is 6 feet above the first mountain range. You even more so can't
see through the mountains. If you move back so you're not crushed and
then bring the two mountain ranges together the volume of material you
are trying to see through is only a tiny fraction thicker. And again you
can't see through the mountains.  You eyes can't tell the difference
between the 6 foot "crack" and no crack. Same for the x-ray system. 

Now if the "crack" in your solder joint is as big as a barn door, that
is the teeth of the solder crack are open so much you could literally
visually see through from one end to the other, you would be able to see
it by x-ray, but in most cases this would just be redundant. 
Bev
RIM

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