Ball Grid Array transistor and strange Paste & Mask patterns

V5.16 KiCAD
I am using a INN100W12 transistor which comes in a package something like WLCSP-16_4X4.
The transistor manufacture demands a pin foot print of:
CU top = 300x350um square (yes that micro meters)
Paste = 250x300um square
Mask = 268um round
I modified to get a WLCSP-15_3X5 with 450x500um pin to pin.
What is the best way to do this? I am thinking of spending the next 4 hours using Graphics Lines or Graphics Polygons to make small rectangles then convert them to Past or Mask and then setting them on top of the pads. It appears I can place a Line very accurately with edit but a Polygon’s location can not be edited.
Is this the thing to do or is there a better way? (I have not use Python.)

You are doing this in the footprint editor I presume?

First, I advise against using square pads and paste layers.
Especially paste, which has the tendency to stick into the corners of the stencil. IEC recommends to use rounded corners.

For the paste you can use a negative offset in the “Local Clearance and Settings” tab of the pad properties.

For the mask, if you want to use a different sort of pad, then just use an extra pad for it, and then disable the copper layer for that pad. This is a common technique in KiCad, and also used for a lot of the library footprints with thermal pads.

I was a bit confused by loading a WLCSP in the footprint editor. It turned out that F.Cu and F.Paste both were the same color. You can change that by double clicking on the colored rectangle in the Layers Manater on the right side of the monitor.

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What a great idea! I now see how to stack up pads to make strange things happen. It appears that CU is easy to edit but other layers are not easy. I could stack up 2 or 3 pads in the same spot. Use copper in pad-1 and mask of pad-2, etc.
There is at least 16 amps in this transistor and some heat. I think the idea is to have as much copper as possible. Then I think they want more solder than normal.

Interesting, then the colors are saved in the foot print? That will solve some more problems I am having with this part?
Thanks, Ron S.

It’s not my idea. It’s common practice in KiCad, and indeed you can make strange things happen with it. :slight_smile:

Currently a pad has just a single graphic shape, and that shape usually is copper. Other layers can be derived from that with either the same shape or a (positive or negative) offset.

No you understood me wrong.
You can change colors of layers, but the settings is for the whole layer, and has nothing to do with the footprint itself.
It’s the same mechanism as changing layer colors in Pcbnew.
It’s just that two different layers were shown in the same color which confused me a bit.

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Not certain what I am going to do but here is my first try. Connecting together some of the pins will make layout better.
Dark red=cu, Bright red=mask, Need to make the silk dashed.