Addressable RGB LED 2020 - Worldsemi WS2812B-2020

@@ -77,6 +77,35 @@ Corners: square, as the datasheet draws them. The datasheet does not call for ro  ::adom-footprint-variants{src="/adom/ws2812b-2020/render/footprint-variants/WS2812B-2020.variants.json" heading="Pad corners: this footprint (square, as drawn) and KiCad default rounding (not used)"} +### Why the pads are smaller than the metal under the part++Looking at the 3D model from underneath, each bottom terminal is longer than the copper pad it lands on, and+the copper runs past the package edge. Both come straight from Worldsemi's datasheet:++- **The terminals:** the Back View (p.1 Mechanical Dimensions) is drawn to scale. Its printed dimensions+  (2.20, 2.00, 1.13 and 1.00 mm) all measure 350 px/mm, and at that scale each bottom terminal is+  0.535 x 0.78 mm, on a 1.00 mm pitch.+- **The pads:** the PCB Solder Pad figure (p.2) prints 0.7 x 0.7 mm pads with a 0.40 mm gap between rows,+  so the pads sit on a 1.10 mm pitch. KiCad's own `LED_WS2812B-2020_PLCC4_2.0x2.0mm` footprint uses the same+  pads (0.7 x 0.7 at x +/-0.915, y +/-0.55).++So, per Worldsemi:++| | Terminal on the part | Pad on the board |+|---|---|---|+| Length along the pin column | 0.78 mm | 0.70 mm |+| Pitch | 1.00 mm | 1.10 mm |+| Outer end | at the package corner side | lines up with the terminal's outer end |+| Inner end | 0.11 mm from the centre line | 0.20 mm from the centre line |+| Beyond the package edge | 0 | 0.165 mm (copper under the castellation) |++The pad covers the outer 0.70 mm of each terminal and leaves the inner 0.08 mm off the copper; the 0.40 mm+gap between rows is what keeps adjacent pins from bridging at this size. The extra 0.165 mm of copper beyond the+body is where the solder fillet climbs the half-round castellation, which is also how the joint is inspected.+The footprint follows the datasheet's pad figure exactly rather than centring the pads on the terminals.++![Worldsemi Back View at true scale with the footprint pads drawn on, beside the PCB Solder Pad figure](docs/img/ws2812-pad-proof.png)+ ## Chip outline  The part's 3D outline in the standard pose (pad 1 toward the viewer), drawn from the STEP by Adom's OpenCascade service; the part number sits where the laser-etched mark is on the 3D model and reads the same way.

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