gEDA-dev: code sprint ideas

[Peter Clifton]

On Mon, 2007-10-15 at 10:17 +0000, Kai-Martin Knaak wrote:
> On Mon, 15 Oct 2007 10:33:18 +0200, Gabriel Paubert wrote:
> 
> >  The problem
> > is that the soldermask patterns pads are still rectangular and this
> > means that the distance between the corners of the soldermask openings
> > and the remaining copper is much smaller than with rectangular ground
> > plane openings.
> 
> Can you enlighten me: Why should the distance to soldermask be greater at 
> corners than at straight copper edges? 

Registration mis-match between the copper and the soldermask printing.

With square + square, the misalignment can be as much as +/- GAP

With square + rounded, the misalignment is not allowed to be as big in
both directions at the same time. (Eg.. if the registration is out both
in the X and Y directions at once, it might mean mask covers the corner
of the pad whilst the X and Y registrations are otherwise in tolerance.
(It seems likely to me that the X and Y registrations are independent
error terms, not some "distance" offset error in registration.
-- 
Peter Clifton

Electrical Engineering Division,
Engineering Department,
University of Cambridge,
9, JJ Thomson Avenue,
Cambridge
CB3 0FA

Tel: +44 (0)7729 980173 - (No signal in the lab!)