In a message dated 08/23/98 2:52:16 PM Pacific Daylight Time,
[log in to unmask] writes:
> Steve, I just wanted to ask, do you use a special CAM software for
> this over/undersize black magic or is it much manual work with
> D-codes editing and transcoding instead of just pressing the
> "undersize button"? The SW I know mostly allows just (semi-)automatic
> oversize/undersize for all selected items for which value I ever
> needs. (If you dont't like "product placement", reply off-line
> please)
>
> Which solder mask oversize do you prefer? (depends on solder mask
> process, screen printing or photo) If I want dams between the pads,
> then I should have as low mask oversize as possible. But then I get
> often PCBs with misaligned solder mask ON the pads....
>
> Thanks
> Matthias
> -----------------------------------------------
> Matthias Mansfeld Elektronik
> * Printed Circuit Board Design and Assembly
> Am Langhoelzl 11, D-85540 Haar, GERMANY
> Phone: +49-89-4620 0937, Fax: +49-89-4620 0938
> E-Mail: [log in to unmask]
> Internet: http://home.t-online.de/home/matthias.mansfeld
Hi Matthias!
I don't want to give the impression that I was the one who actually does the
edits to the gerber for my stencil, my stencil vendor (Beam On Technology)
does.
I take the gerber that's given to me by our customer, look at it with a free
viewer that I downloaded off the net (lavenier viewmate) so I can see what
opening sizes there are on the gerber, and then tell my stencil vendor what I
want done to what.
They use some software called ECAM, but I think maybe that's manual too...as
they have a charge for edits like that. It's not much of a charge, but I guess
to do that does take some time that they need to get paid for.
As for a gap distance between the mask and the pad, that's easier defined by
saying whatever distance is best to enable the fab vendor to get a line of
mask down between the pads and have it stick to the board reliably...just
about any width of dam works as long as it's between the pads and stays there.
If you listen to the mask suppliers claims, they say their products can do
2-mil dams, if I were to walk into a fab house and say I want 2-mils dams, I'd
probably be laughed out of their shop...I'm into asking for what is reasonably
doable by a fab shop. So I guess that means that I would find out where the
boards were gonna get built and ask them what kind of resolution they're
capable of with solder masks. I know that ain't much of an answer, but it's
hard for me to settle on a set distance with the varying capabilities of PCB
vendors out there.
-Steve Gregory-
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