Feature Request: Square Pad With Clipped Corner

Bug #855988 reported by Stephen
42
This bug affects 9 people
Affects Status Importance Assigned to Milestone
KiCad
Fix Released
Wishlist
Unassigned

Bug Description

There are ICs that require a thermal pad under them. In recommended footprints this thermal pad also functions as a pin one indicator where either a semi circle is recessed into an edge as shown on page 48 of this document:
http://www.silabs.com/pages/DownloadDoc.aspx?FILEURL=Support%20Documents/TechnicalDocs/C8051F31x.pdf&src=DocumentationWebPart
or with a clipped off corner as Mentor Graphics does it as shown for QFN packages in their LP Viewer. A similar way is needed to do this in Kicad.

Revision history for this message
Lorenzo Marcantonio (l-marcantonio) wrote : Re: [Bug 855988] [NEW] Feature Request: Square Pad With Clipped Corner

On Wed, 21 Sep 2011, Stephen Pflanze wrote:

> Public bug reported:
>
> There are ICs that require a thermal pad under them. In recommended footprints this thermal pad also functions as a pin one indicator where either a semi circle is recessed into an edge as shown on page 48 of this document:
> http://www.silabs.com/pages/DownloadDoc.aspx?FILEURL=Support%20Documents/TechnicalDocs/C8051F31x.pdf&src=DocumentationWebPart
> or with a clipped off corner as Mentor Graphics does it as shown for QFN packages in their LP Viewer. A similar way is needed to do this in Kicad.

You can do these composing pads: a trapezoidal pad can be used to make
the triangular part and two other pads will close the rectangle like
this:
      ______
  /| | |
/_| |______|
  __________
| |
|__________|

I've done this for similar QFN and it works perfectly... a 'native' pad
like that could be added as a wishlist item.

--
Lorenzo Marcantonio
Logos Srl

Martin Errenst (imp-d)
Changed in kicad:
importance: Undecided → Wishlist
Revision history for this message
Martin (mm1262) wrote :

The requirement for clipped corner pads is also needed for very small footprint QFN packages such as the 4mm x 4mm UFQFPN28 package for the STM8L151.

An option to solve this would be to provide the capability to build drawn pads (actually, it would be very nice to have a pad editor to create nearly any custom pad shape required by a footprint). This was a capability (i.e., custom drawn pads) I used extensively in Cadnetix 15-20 years ago.

Revision history for this message
Lorenzo Marcantonio (l-marcantonio) wrote : Re: [Bug 855988] Re: Feature Request: Square Pad With Clipped Corner

On Tue, Apr 29, 2014 at 07:17:38AM -0000, Martin wrote:
> An option to solve this would be to provide the capability to build
> drawn pads (actually, it would be very nice to have a pad editor to
> create nearly any custom pad shape required by a footprint). This was a
> capability (i.e., custom drawn pads) I used extensively in Cadnetix
> 15-20 years ago.

Wishlist... you can do that with some work and trapezoidal pads, at the
moment.

--
Lorenzo Marcantonio
Logos Srl

Revision history for this message
Ian Muldoon (inio-m) wrote :

Composing pads is fine for the copper layer, but fails pretty badly on the mask and paste layers. In the mask layer you get corners jutting out oddly, and on the paste layer you get a collection of tiny apertures that won't do what you want.

Revision history for this message
Seth Hillbrand (sethh) wrote :

This appears to be corrected by Tom's compose pads commit ac095b672

@inio-m can you test whether your issues are resolved by this?

Revision history for this message
Nick Østergaard (nickoe) wrote :

@Seth, how you tested this? I can't seem to make this work.

I assume it is the "Create Pad from Selected Shapes" context menu item. I can't make it work with multiple overlapping SMD pads.

Revision history for this message
Nick Østergaard (nickoe) wrote :

I get the error message:
"Cannot convert items to custom-shaped pad: selection contains more than one reference pad."

Revision history for this message
Seth Hillbrand (sethh) wrote :

@nickoe You can compose the pad out of a polygon. Start with a single SMD pad and add a polygon primitive.

Seth Hillbrand (sethh)
Changed in kicad:
status: New → Fix Committed
Revision history for this message
Nick Østergaard (nickoe) wrote :

Hmm, ok. I was not really aware how the feature worked. I suspect we really should ensure it is documented in the user docs also, eventually.

Changed in kicad:
status: Fix Committed → Fix Released
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