[sdiy] smallest font sizes for pcb

[Joe Grisso]

Hi Danjel,

     For my through-hole work, I keep my fonts >60mil, and either a
10:1 or 10:1+2mil ratio between font size and line width. The average
is an 80/8 font with 100/10 for ICs and 100/12 for connectors. For my
surface mount stuff, I try to keep everything in the 50-70mil size for
serviceability, but will go down to 40mil and a 5mil line size if need
be. My line widths rarely go below 6 mil.
     The reason for this is because the same photoplotting machine
that draws the copper does the silkscreen. If you have a board
specification of 6/6 (6mil trace/6mil space) and then you have a 30/3
font for your silkscreen, you're going to get 30/6 and a lot of DRC
violations in whatever tool they use, so your board vendor will
automatically flag the error and stop the job. I also took a moment to
look at 30/6 in my PCB tool. The numbers, while legible in the tool,
might not be with the small amount of bleed and smear a silkscreen has
when it's applied to a PCB. I figure the reference designators would
be blurry and require a magnifier of some kind for most techs these
days.

Best,

-- 
Joe Grisso
Detachment 3 Engineering

On Mon, Dec 21, 2009 at 5:13 PM, Danjel van Tijn <danjel at gmail.com> wrote:
> I am having an issue with boards at PCBcart with text they say is too small.
>
> What is the smallest font+ratio size I should get away with? They were
> suggesting >30mil but this seems pretty big.
>
>
> cheers,
> Danjel
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