Hi
Steve,
I didn't know that
Smart Modular Technologies was no more. I just spec'd in some of their
DIMM's about 6 months ago. With regard to the X-outs being randomly placed
and not machine readable, I did some work a while back for a contract
manufacturer who had just put in place a system to "fix" this problem.
Their solution, which seemed pretty clever to me, was to place a diamond-shaped
fiducial on each board in the panel, and then, you guessed it, have the PCB
fabricator black out just the little diamond. So rather than a big
randomly placed "X", which is great for us near-sighted humans, you got a small
paint or ink blob on the fiducial. I don't know where on the process line
they read the diamond-shaped fiducial to tell all the subsequent machines about
the bad board locations. But it did seem like a really good idea (like
most ideas that I don't have to implement). Your point about solder paste
is well taken. That one seems pretty hard to avoid without spending more
than you could save.
Regards,
Seth Goodman
Goodman
Associates, LLC
tel 608.833.9933
fax 608.833.9966
Hi
Stacy!
Having read the replies that you've recieved so far, they are
giving you good information. The only thing I can add is some past experience
from my employment at a memory company...Smart Modular Technologies, they are
no longer, was bought out by Solectron...but I digress...
As far as
X-outs, they aren't free. The FAB house won't charge you for them, and your
bare costs may be lower, but there are costs that you will see on your
production floor from X-outs.
Normally what I see from the fab houses
is a big "X" drawn on the individual boards. That X is something that we can't
program our machines to see since it's not consistently in the same place. We
normally had to sort the panels one-by-one and put a label that the machine
can see on each of the x-outs, at a consistent location, so the machine don't
try and populate bad boards.
The other alternative is to sort the fabs
according to which boards are bad, and then have separate programs that
populate only the good boards...either way, you still have to handle each
board.
The other thing to think about is the wasted solder paste that
you print on these bad fabs. It may seem insignificant, but when I worked at
Smart Modular, we would sometime do almost a million modules a month during
our busy times. I did a calulation of the solder paste that was wasted on bad
boards over a years time, and it was close to $50,000 a year!
It's not
only that, you need to figure in the time that's wasted in depaneling. You say
you have a router inline that depanelizes everything, does it do only the good
boards, or does it do the whole panel? Is it wasting time routing out bad
boards?
X-out aren't a big deal in low volumes, but if you do high
volumes, the costs that you may save in the bare board costs may be
insignificant compared to what you spend on the production
floor...
-Steve Gregory-