In a message dated 12/30/98 5:48:43 PM Pacific Standard Time, [log in to unmask]
writes:
<< Happy New Year Technetters!
Does anyone have information or recommendations for designing
depanelizing fixtures used to manually depanelize (i.e., snap, break
away).062 thick, scored, PCBs. Without fixturing, there is a problem
with capacitors cracking.
Thanks!
Enza >>
Happy New Year to you and everybody else too!
Are ya'll ready to party like it's 1999 as sung by that guy...what's his name?
Uhh...some artist formally known as? I can't 'member his name... Ponce?
Prance? Poonce? oh well...(GRIN)
What I'm wondering Enza, is if your board is scored correctly. If it's not
scored properly, you'll see that...and you'll be getting a fixture that you
don't really need.From what I've learned, most specify a score that's a third,
a third, and a third. That is to say you have a score depth that's a third of
the board thickness from one side, a third from the other, and leaves a web of
a third of the material. That may work sometimes, but how well that works
depends on the glass fiber weave density, the diameter of the fibers, resin
used in the laminate, etc.
If the board is scored to the correct depth, done cleanly with a nice sharp
blade, and both scores line up over each other, it should break away easily
without stressing the caps to the point that they're fracturing. I've got a
chart that was given to me a while back from a gentleman named Dennis Johnson
who has a company called Onanon. They're located out here in Silicon Valley in
Milpitas. Onanon does nothing but drill, route, and score...he's getting into
more complex machining now, but started the business just doing PCB's. 3COM
was having all their PCMCIA Fabs drop-shipped from their Fab vendor to Onanon
to get their scoring done...and in fact, asked Dennis to determine how close
to a score line you could place a capacitor and not worry about damage, that's
where the chart came from. He's learned more and added more data to the chart
and will be posting the chart on their WEB site soon. I've used the chart he
created earlier and it's worked very well for me whenever anybody has asked
about specifying a score depth. One thing you might do until you find a
resolution to your problem was what Dennis suggested to me with the same
problem you have.
You see, I recieved a kit from a customer a couple weeks ago that wasn't
scored deep enough. Being a consigned kit, we don't normally do any real
incoming inspection on fabs or anything, we expect to be given good fabs and
parts. We just count the parts (that's going to change a bit after what
happened). To make it short, we built the boards and found that we couldn't
depanelize them without an extreme amount of force. I took a panel over to
Dennis to see if he could go back and rescore them for me (he's done that for
me before, and one of the ONLY companies I've found that would even try to
score loaded assemblies). But because the panel had a slight warp from wave
soldering and some other issues, he said that he wouldn't be able to do a good
job. But he told me that if I took a nice sharp exacto knife and made a couple
of passes down the score lines, I should be able to get the additional depth I
needed to separate them without damage. Be sure not to try and cut too deep
with each of these passes, it gets harder to control where that blade goes the
more pressure you use...you sure don't want to slip and wind-up cutting a
trace or something. If after a couple of passes you still are flexing the fab
trying to depanelize it, go back and make a couple more passes until you can
break it away without the flex. It worked great for me, but I also didn't have
thousands of panels to do...I don't know what kind of quantities you're
dealing with.
Onanon's WEB page is: http://www.onanon.com
and can be reached at: (408) 262-8990
I hope this'll help ya' a bit...
-Steve Gregory-
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