In a message dated 10/01/98 6:25:26 PM Pacific Daylight Time, LonerLSZ writes:

> Steve,
>  We do a percentage of lot inspection for ISO.  If you are considering
> becoming certified then you will need to do process control which will
> require a need for inspection.  BGA's can only be inspected by x-ray so how
> else would you do it?
>
>  Linda

Hi Linda!

    How would I do it you ask? Easy, we got this guy workin' for us named
Clark Kent and he...what?....not buyin' that are ya?...didn't think ya
would...hehehe.

Seriously, my logic is that when you're pumping out production boards, you
should have your processes dialed-in.

Production scenario: You've got your stencil tweeked, paste is just the stuff
you want, and you know you can print 15 times and then program a cleaning
cycle to keep the image crisp. You also know that each print takes 3-grams of
paste, so you'll program a dispense cycle in every 30 prints to keep a nice
roll of paste in front of the squeegee. You know your placement programs are
dead on because they came from cad data, you also verified that on your first
article. Reflow profile was created, plotted, and given a fine adjust for the
first article, which was followed with the xray inspection. Now you're gonna
run some revenue.

You've got your people doing periodic, random, process checks and logging them
after solderpaste print, placement, and reflow, and they're doing a great job
making sure that happens. So you tell me, when should I fire up the ol' x-ray
machine again? When would I r-e-a-l-l-y need to if what I described above was
happening? See my point? Things normally don't all of a sudden go wacko for
three boards and fall back in line again. If you have your process set and
being monitored, I have a hard time coming up with a good reason to justify x-
ray for anything other than initial process set-up and verification. If you
find something during a production run, in my mind, it's too late. What would
you do? Stop production and go back and x-ray all the boards that were built
from the last time a board was
x-rayed?

Don't get me wrong, I'm not saying what you're doing is a waste, but these are
things that I've been thinking about trying to really justify the expense of a
x-ray. Will it really be earning it's keep while every other machine is
producing something? Food for thought huh?

-Steve Gregory-

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