kicad-developers team mailing list archive

[Vesa Solonen <vsolonen@...>]

On Fri, 12 Mar 2010, viking632 wrote:

> I've added the DB-9,15,25,37 and the
> DSUB15 ("VGA") connectors, and the TO220-11.

Very nice! Your module work is just outstanding amd all my new designs are 
going to use them as much as possible.

> Now, the pin #s floats above each pin (male) or inside
> the hole (female), which is a lot easier to do :-)

Excellent.

> Also, I've renamed the resistors, so
> the name only reflects the pin spacing.
> I didn't like the naming, and someone also pointed out that the
> wattage doesn't uniquely determine the resistor package size.

That someone was me and my special thanks goes to your work on capacitors.

> There are a number of issues that I would like som opinions on:
>
> * The pins on TO126 and TO220-5 are spaced quite close together.
> I think the solution for TO126 is to reduce the pads slightly,
> and I could do the same with the TO220-5, or I could zigzag the
> TO220-5 pads, like on the TO220-5R (but by only one pin-pitch) ?

I think we should supply both variants as commercial PTH boards can use 
very small pads and it is even advantageous (less solder), but for hobby 
and hombrew use even non standard pin forming may be ysed advantageously. 
Exact pad size and clearances come from design rules anyway, so library 
may be designed as a good defaults in mind.

> * The current libraries provides several versions of the
> TO92 and TO18 with varying pin mappings, something that
> IMHO should be taken care of in eeschema or cvpcb,
> by providing a mapping from pin function to pin number.
> The TO3 in the current libs also maps the pins wrong:
> The house is numbered #1, and pin #1 is numbered #3.
> Are anyone looking into such a function-to-pin mapping, or
> should I provide (horrors) the -CBE, -EBC, -DGS, etc. variants ?

That pin mapping functionality is not yet there, but if those with greater 
coding skills agree with my proposal it will be some day. Along with pin 
swapping, etc. That's my long term goal anyway. Footprint library should 
just stick to the standard numbering and nothing else. Otherwise the 
system is a mess after a while. Anyway it's few clicks of work to change 
schematic symbols pin numbering, so that should be the way.

> * General guidelines on pin size to drill hole and Pad sizes ?
> I found a site that suggested Pad size == 2*pin size
> (or smaller if the spacing doesn't permit that).
> What about drill holes ? Is pin+0.1mm OK, or pin+0.2mm ?
>
> Ã?yvind.

I can not give a definitive answer to that, but some sane defaults might 
be 2 times pin size and pin+0.1mm. Even better might be just to specify 
the pin diameter with tolerances and specity that. The exact diameter 
depends on hole plating too and it would be quite easy to fix the whole 
PCB hole sizes after the layout with a manufacturing helper script.

For my home made PCBs 0.8mm is a general hole with 66 or 70 mil pad so it 
turns out to be about 2.1 times the hole size. It's adjusted case by case.

BTW, if you have time to add horizontal and reverse horisontal (thermal 
pad upwards) plastic flat TO-packages (TO126, TO220...) to your library 
I'd be very delighted. They allow all kinds of very usable layouts with 
heat sinking.

Best regards,
-Vesa