kicad-developers team mailing list archive

[Cirilo Bernardo <cirilo.bernardo@xxxxxxxxx>]

Hi Michal,

 Since the exposed pad is often a thermal tab, you must use one
solid shape for the pad itself. It is the solder paste stencil which
you must break into multiple apertures. In such cases it's also
convenient to have tented thermal vias (maybe there's a way to do
this with pads) and a heat tab on the opposite side of the board
as well.

- Cirilo

On Mon, Aug 31, 2015 at 3:21 AM, nnn <nnn4000@xxxxx> wrote:

> It may be better to make exposed pad as array of smaller pads for better
> application of solder paste. This will also allow to easily change the pad
> into array of tht pads for improved power dissipation. Below - how I did it
> in C (full code here:
> https://github.com/michal777/KiCad_Footprint_Generator). I think exposed
> pad should be numbered max+1 because sometimes there are more exposed pads.
>
>
>     if((exposed_pad_x != 0) && (exposed_pad_y != 0))    //if there is
> exposed pad, make subdivision
>     {
>         exposed_pad_part_size_x = exposed_pad_x / exp_pad_subdiv_x;
> //size of one part of exposed pad
>         exposed_pad_part_size_y = exposed_pad_y / exp_pad_subdiv_y;
>
>         exposed_pad_part_1_x = exposed_pad_part_size_x / 2 +
> exposed_pad_part_size_x * exp_pad_subdiv_x / 2 -
> exposed_pad_part_size_x;    //calculate positon of first part of exposed pad
>         exposed_pad_part_1_y = exposed_pad_part_size_y / 2 +
> exposed_pad_part_size_y * exp_pad_subdiv_y / 2 - exposed_pad_part_size_y;
>
>         for(ep_cnt_x = 0; ep_cnt_x < exp_pad_subdiv_x; ++ep_cnt_x)
> //generate exposed pad array
>         {
>             for(ep_cnt_y = 0; ep_cnt_y < exp_pad_subdiv_y; ++ep_cnt_y)
>             {
>                 fprintf(footprint_file, "  (pad %d smd rect (at %s %s)
> (size %s %s) (layers F.Cu F.Paste F.Mask)\n", pad_number,
> f2c(exposed_pad_part_1_x - ep_cnt_x * exposed_pad_part_size_x),
> f2c(exposed_pad_part_1_y - ep_cnt_y * exposed_pad_part_size_y),
> f2c(exposed_pad_part_size_x), f2c(exposed_pad_part_size_y));
>                 fprintf(footprint_file, "    (solder_paste_margin_ratio
> %s))\n", f2c(exp_pad_paste_ratio));
>             }
>         }
>     }
>
>
>
> W dniu 29.08.2015 o 21:37, easyw pisze:
>
> Hi,
>
> Here is the patch vs revision 6132 for adding exposed pad to qfp_wyzard
>
> I added the exposed pad option and changed name from QFP to QFP/QFN.
> I used the function PadLineArray because I couldn't find the apis doc...
> anyway it should be fine.
> I assigned 0 to exposed pad pin number...
> please let me know if it is fine or if I should change it to maxpin number
> +1.
>
> Thank you,
> Maurice
>
> On 23/08/2015 17.29, jp charras wrote:
>
> Le 23/08/2015 16:41, easyw a écrit :
>
> Hi JP,
>
> The changes are fully working.
> thanks for committing.
>
> PS
> I see you added a bar code generator to fp wizard...
> Do you think it would possible to add also an option for exposed pad in
> qfp/qfn footprint?
> thank you
> Maurice
>
>
> Yes, I think this is a good idea.
>
>
>
>
>
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