Dennis & others,
The one thing I believe that I was the only one to mention was the
fabrication tolerance. Particularly on multi-layer boards. Dennis, your figures
are OK but a little tight when you throw in the fabrication tolerance which is
typically 3 - 5 mils for multilayer. Then you could be prone to break-out on
vias if their fabrication spec is 5 mils. Also add into that any tolerance for
drill location and you will surely have some breakouts somewhere in that board.
Typically I use a simple annular ring of 7 - 7.5 mils and thus it gives you a
bit more allowance for the fabrication allowance as well.
On the silkscreen that is about the same sizing that I have used for a
minimum, I have gone to 25/5 (height/width) on occasion. Although with the
shops I use, they simply use a photo-imageable silkscreen material to achieve
the small text size. The make or break between normal and photo-imageable
silkscreen seems to be approx. 35/7 (height/width) text. Simple ratio to
remember for readable silkscreen text, 5:1. Or for a complex letter/number
(i.e. 8, 3, S, etc.) equal line, break, line, break, line. So with that in mind
I would think your fabricator could possible go as low as 20mil height using
the 4 mil lines.
Sincerely,
Brad Velander
Senior PCB Designer
Northern Airborne Technology
1925 Kirschner Rd.,
Kelowna, BC, V1Y 4N7.
tel (250) 763-2329 ext. 225
fax (250) 762-3374
-----Original Message-----
From: Dennis Saputelli [mailto:[EMAIL PROTECTED]
Sent: August 4, 2005 7:22 AM
To: Protel EDA Discussion List
Subject: Re: [PEDA] Vias.
but Igor
i do 4 & 6 layer bds all the time at a local shop with 22 mil dia and 12
mil holes
they don't complain (or charge more as far as i know) and the holes are
even well centered
and don't forget that 15 drill plates to 12 mil dia
but you are correct that 1 mil does make a big difference because when i
tried to push him to 20/10 he said no!
(i know other shops will do this though)
Dennis Saputelli
PS
as an aside this same shop has what they call a 'direct image' printer
(or some similar term, i forget exactly) for the 'silkscreen'
it is essentially a specialized inkjet printer
this allows the legend characters to go down to something like 32/4
(height/width in mils) as i remember and i think even smaller is
possible w/ certain printers
the appearance is a bit wimpy (the ink does not appear to be dense) but
it is legible and goes where silkscreen never could
Dennis Saputelli
_______________________________________________________________________
Integrated Controls, Inc. Tel: 415-647-0480 EXT 107
2851 21st Street Fax: 415-647-3003
San Francisco, CA 94110 www.integratedcontrolsinc.com
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