kicad-developers team mailing list archive

[Lorenzo Marcantonio <l.marcantonio@xxxxxxxxxxxx>]

On Fri, Feb 13, 2015 at 10:09:55PM +0100, Mathias Grimmberger wrote:
> The radius of the rounded corners is fixed at 25% of the shorter pad
> edge, but not larger than 0.25 mm. I'm not sure whether the radius needs
> to be adjustable.

Yep, that's the IPC recommendation for round corner rectangular pad.
It's in fact now the preferred one over the oblong (finger, oval,
whatever) and rectangular ones since it has more surface for forming the
joint. The rectangular pad is meant to be used when the pad needs to be
trimmed for clearance. The reason is as follow:

- More surface => better joint area, but
- Rounded corners => better mechanical properties (esp. vs delamination)
  and fillet shape

So rounded corners are better *unless* you need to trim the pad (so you
use the square corners to maximise pad surface).

The adjustable radius *could* be useful for thermal enhanced packages
(heat slugs), like those in MO220. JEDEC doesn't specify a radius (since
it's a package, not a land pattern), but some manufacturer quote the
radius for the heat slug pattern.

So if it's cheap to do it, put it in; otherwise you could always use
a rectangular pad or combine some oblongs.

Anyway, surely a useful addition, thanks

-- 
Lorenzo Marcantonio
Logos Srl

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