> > Optimal pad size seems as a minimum twice the diameter of the hole, thr=
ee
> times
> > maximum (if board space allows).
>=20
> I like to think in terms of the "trace width" of the ring around the hole=
..=20
> Obviously this shouldn't be any smaller than the minimum trace width supp=
orted
> by the manufacturer, and should generally be significantly larger to allo=
w for
> easy soldering, and significantly larger again for mechanical strength if
> there are heavy components or external stress (connectors) involved.  Sin=
ce a
> "typical" min trace width is 0.2mm, and a typical hole is 0.8mm, your "tw=
ice"
> allows for a ring width of 0.4mm, which is OK.  I usually fiddle with EAG=
LEs
> DRC parameters when I'm otherwise done, and make the rings as wide as I c=
an
> without running into clearance issues.  OTOH, that's partially because I'=
m
> aiming at users with less soldering experience.
>=20
> EAGLE defaults to 25% of hole size for the ring (1.5x hole diameter for t=
he
> pad), tempered by a minimum ring width...
>=20

Designspark has a drill backoff check as one of the design rule checks. Thi=
s=20
checks the following for pad diameter, ring hole and track width connected =
to=20
the pad:

P is the diameter of the pad, D is the drill diameter and T is the track wi=
dth.=20
If T/2 (the radius of the track end) is greater than (P-D)/2 (the track wid=
th=20
of the pad) there is a drill backoff error.

This is because the track end is rounded (diameter=3Dtrack width) and it is=
=20
backed off so the rounded end just touches the hole during the plotting out=
put=20
stage. If the track is too wide or the pad diameter is too small, the track=
 has=20
to be backed of so far that there are two small cuts between the track and =
the=20
pad. This can cause over-etching during manufacture.

If this would happen, designspark does not backoff the track so the track=20
coveres the drill hole.

I don't know if this really is a problem or even if the board manufacturers=
=20
does plot the layout with holes in the pad.

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Ruben J=F6nsson
AB Liros Electronic
Box 9124
200 39 Malm=F6 Sweden
www.liros.se
Tel +46 40142078
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

--=20
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