Hi, Dave,

X-Ray inspection, even using the best 3-D computer enhanced types with an
expert operator are very hard pressed to detect micro-cracking of joints -
unless you can use a dye-penetrant that shows up on x-ray, and won't affect
solder joints in you opt to reflow the BGA exhibiting cracking. Never tried
it so don't  know of such a dye.

A number of (jumbled) thoughts occur, though this is bordering on the
limits of my experience:

1. If your boards are designed for ICT testing, Agilent, at least, has a
technique for measuring the tiny capacitances in solder joints that tells
you whether or not you have cracks. Not sure how they apply this to BGA's
though, but it might be worth asking them. That would be your means of
capturing the problem in Production.
2. Have you done any peel-testing as part of your soldering process
qualification? Did you use a dye penetrant before the peel? That would also
show up any pre-existing cracks that are there.
3. Microsectioning a board that shows intermittent or variable electrical
properties to see what the story is?
4. Dry joints? Flux type? Inappropriate thermal profiling?

Not much help, but some I hope.

Peter



David Harman <[log in to unmask]>   25/01/2003 09:44 AM
Sent by: TechNet <[log in to unmask]>

Please respond to "TechNet E-Mail Forum."; Please respond to David Harman

              To:  [log in to unmask]
              cc:  (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
              Subject: [TN] BGA micro cracks














Here is my issue.





We have a CM that x-rays 100% of the BGAs on our product and notes no
abnormalities. We might have some micro cracking at the ball joints.  (This
was discovered because the product electrical properties are intermittent
when we press the BGA down.).  In addition to having our CM x-ray the board
we had an outside company perform this inspection with the same results.
If it is not micro cracking we are un-clear what else can be causing this
abnormality.





Any suggestions on how and what we can do to capture this abnormality in
production?


What type of screening can be done after production? (We have performed a
static thermal testing (-0 to 125 degrees) with no failures after testing.


What other type of testing or inspection can be performed to evaluate ball
joints on BGAs?





Thanks David.





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