kicad-developers team mailing list archive

[Lorenzo Marcantonio <l.marcantonio@xxxxxxxxxxxx>]

On Mon, 30 Aug 2010, Alex G wrote:

> Thanks again. It's a pretty handy tool, I must admit.
>
> Ok, so for an M3 washer it yields:
> 7.3mm pad for 3.1mm hole (tight fit) with 7.6mm courtyard
> 7.7mm pad for 3.5mm hole (loose fit) with 8.0mm courtyard
> Interpolating, I guess it should be
> 7.4mm pad for 3.2mm hole with 7.7mm courtyard
>
> Courtyard is defined as:
> > The area that provides an electrical and mechanical clearance around the component body and land pattern boundaries.
>
> So I'm assuming this means "don't put any tracks in that zone". I'm not
> sure, but I think kicad allows setting pad clearances that are different
> than the net values.

No, it's keep that area free of exposed stuff. Tracks under solder mask
can go there, exposed track or mechanical stuff don't. Also the
courtyard is strictly rectangular. The underlying idea is that courtyard
is needed for tooling (hot air nozzles, BGA reworkers and so on).

Since you're not tooling a single hole, just disregard the courtyard.
Electrical clearance isn't stated by IPC but depends on your process
*and* on the voltages running on the pad (look around the net for
creepage and insulation for details, for SELV work it doesn't apply
anyway).

> While the tool allows for calculating land patterns for screw heads and
> washers, there's no option for nuts (no pun intended).

Nuts are like washers since you need the space for the wrench:D At
least, that's my theory. More than one time I had to change the layout
because the board couldn't be fixed (typical issue: a big capacitor in
the wrench travel area and no other way to turn it).

> Going back to our DSUB connectors with 3.2 mm mounting holes, I guess
> this means a 7.4mm pad with a minimum clearance of 0.15mm.
> Lorenzo, I'm expecting a confirmation or a "you got it totally wrong you
> idiot!!!" . :-p

Your clearance is for a 6mil process (the default for the IPC
calculator); nothing esoteric but if I can I prefer an 8mil process
(0,2mm) since it's cheaper for mass production; also 6mil isn't done by
some 'hobby' manufacturer... I don't know your library standard, just
try to be consistent.

In our experience with an 8mil process and 0,4mm vias you can do most
stuff included 0,5 pitch TQFP and some VQFN. For BGA work I'd require
6mil (or 4mil, depending on how much pin you need to fan out:D). IIRC
4mil is the limit for 'standard' processing (at a premium rate,
anyway!).

3.2mm is the correct hole for a M3 screw and 7,4mm seems fine for
a washer pad (the washer itself is 7mm, BTW). So yes, I agree with your
data.

As a bonus here is a production tested HDE15 female, right angle dsub
(done from Tyco specs IIRC). Since it's a snapon boardlock, so no special
handling for fixing screws, only a hole.

$MODULE HDE15-F-RA
Po 11811 49213 0 15 4BD826B3 4BD826BF ~~
Li HDE15-F-RA
Cd High-Density D-Sub, 15-poles, Right Angle
Sc 4BD826BF
AR 
Op 0 0 0
T0 0 0 394 394 0 39 N V 21 N"HDE15-F-RA"
T1 0 0 394 394 0 39 N I 21 N"HDE15-F-RA"
DS -5866 0 -5866 2362 60 21
DS -5866 2362 -3976 2362 60 21
DS -3976 2362 -3976 0 60 21
DS 3996 0 3996 2362 60 21
DS 3996 2362 5866 2362 60 21
DS 5866 0 5866 2362 60 21
DS 6142 0 -6142 0 60 21
DS -6142 0 -6142 -6417 60 21
DS -6142 -6417 6142 -6417 60 21
DS 6142 -6417 6142 0 60 21
DS 3248 2362 3248 0 60 21
DS -3248 2362 -3248 0 60 21
DS 3248 2362 -3248 2362 60 21
$PAD
Sh "" C 1260 1260 0 0 0
Dr 1260 0 0
At STD N 00E0FFFF
Ne 0 ""
Po 4921 -3504
$EndPAD
$PAD
Sh "" C 1260 1260 0 0 0
Dr 1260 0 0
At STD N 00E0FFFF
Ne 0 ""
Po -4921 -3504
$EndPAD
$PAD
Sh "6" C 709 709 0 0 0
Dr 472 0 0
At STD N 00E0FFFF
Ne 0 ""
Po 2150 -3504
$EndPAD
$PAD
Sh "7" C 709 709 0 0 0
Dr 472 0 0
At STD N 00E0FFFF
Ne 0 ""
Po 1248 -3504
$EndPAD
$PAD
Sh "8" C 709 709 0 0 0
Dr 472 0 0
At STD N 00E0FFFF
Ne 0 ""
Po 346 -3504
$EndPAD
$PAD
Sh "9" C 709 709 0 0 0
Dr 472 0 0
At STD N 00E0FFFF
Ne 0 ""
Po -555 -3504
$EndPAD
$PAD
Sh "10" C 709 709 0 0 0
Dr 472 0 0
At STD N 00E0FFFF
Ne 0 ""
Po -1457 -3504
$EndPAD
$PAD
Sh "1" C 709 709 0 0 0
Dr 472 0 0
At STD N 00E0FFFF
Ne 0 ""
Po 1697 -4504
$EndPAD
$PAD
Sh "2" C 709 709 0 0 0
Dr 472 0 0
At STD N 00E0FFFF
Ne 0 ""
Po 799 -4504
$EndPAD
$PAD
Sh "3" C 709 709 0 0 0
Dr 472 0 0
At STD N 00E0FFFF
Ne 0 ""
Po -102 -4504
$EndPAD
$PAD
Sh "4" C 709 709 0 0 0
Dr 472 0 0
At STD N 00E0FFFF
Ne 0 ""
Po -1004 -4504
$EndPAD
$PAD
Sh "5" C 709 709 0 0 0
Dr 472 0 0
At STD N 00E0FFFF
Ne 0 ""
Po -1906 -4504
$EndPAD
$PAD
Sh "11" C 709 709 0 0 0
Dr 472 0 0
At STD N 00E0FFFF
Ne 0 ""
Po 1701 -2504
$EndPAD
$PAD
Sh "12" C 709 709 0 0 0
Dr 472 0 0
At STD N 00E0FFFF
Ne 0 ""
Po 799 -2504
$EndPAD
$PAD
Sh "13" C 709 709 0 0 0
Dr 472 0 0
At STD N 00E0FFFF
Ne 0 ""
Po -102 -2504
$EndPAD
$PAD
Sh "14" C 709 709 0 0 0
Dr 472 0 0
At STD N 00E0FFFF
Ne 0 ""
Po -1004 -2504
$EndPAD
$PAD
Sh "15" C 709 709 0 0 0
Dr 472 0 0
At STD N 00E0FFFF
Ne 0 ""
Po -1906 -2504
$EndPAD
$EndMODULE  HDE15-F-RA


--
Lorenzo Marcantonio
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