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fix: QFN footprint pad sizing to match KiCad IPC standards #416

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fix: QFN footprint pad sizing to match KiCad IPC standards #416

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716dfeb
fix: QFN footprint pad sizing to match KiCad IPC standards
RaghavArora14 Nov 10, 2025
7e18332
Merge branch 'main' into fix-qfn-pad-sizing-clean
RaghavArora14 Nov 10, 2025
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27 changes: 23 additions & 4 deletions src/fn/qfn.ts
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Original file line number Diff line number Diff line change
@@ -1,12 +1,31 @@
import type { AnySoupElement } from "circuit-json"
import { base_quad_def, quad, quad_def, quadTransform } from "./quad"
import { base_quad_def, quad, quadTransform } from "./quad"
import type { z } from "zod"

export const qfn_def = base_quad_def.extend({}).transform(quadTransform)

export const qfn = (
parameters: z.input<typeof qfn_def>,
raw_params: z.input<typeof qfn_def>,
): { circuitJson: AnySoupElement[]; parameters: any } => {
parameters.legsoutside = false
return quad(parameters)
raw_params.legsoutside = false

// Apply QFN-specific pad sizing if not explicitly provided
// Based on KiCad IPC standards for QFN packages
if (!raw_params.pw && !raw_params.pl) {
const pitchValue =
typeof raw_params.p === "string" ? parseFloat(raw_params.p) : raw_params.p

if (pitchValue) {
// KiCad IPC standard for QFN:
// - Pad width = 0.5 × pitch
// - Pad length = 0.8mm
// - Pads extend ~0.35mm beyond package edge for proper soldering
raw_params.pw = pitchValue * 0.5
raw_params.pl = 0.8
// Offset pads 0.35mm further from center so they extend beyond package edge
raw_params.padoffset = -0.35
}
}

return quad(raw_params)
}
7 changes: 5 additions & 2 deletions src/fn/quad.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@ export const base_quad_def = z.object({
pl: length.optional(),
thermalpad: z.union([z.literal(true), dim2d]).optional(),
legsoutside: z.boolean().default(false),
padoffset: length.optional(), // Additional offset for pad position (positive = further from center)
})

export const quadTransform = <T extends z.infer<typeof base_quad_def>>(
Expand Down Expand Up @@ -80,8 +81,9 @@ export const getQuadCoords = (params: {
p: number // pitch between pins
pl: number // length of the pin
legsoutside?: boolean
padoffset?: number // Additional offset for pad position
}) => {
const { pin_count, pn, w, h, p, pl, legsoutside } = params
const { pin_count, pn, w, h, p, pl, legsoutside, padoffset = 0 } = params
const sidePinCount = pin_count / 4
const side = SIDES_CCW[Math.floor((pn - 1) / sidePinCount)]
const pos = (pn - 1) % sidePinCount
Expand All @@ -92,7 +94,7 @@ export const getQuadCoords = (params: {
const ibh = p * (sidePinCount - 1)

/** pad center distance from edge (negative is inside, positive is outside) */
const pcdfe = legsoutside ? pl / 2 : -pl / 2
const pcdfe = (legsoutside ? pl / 2 : -pl / 2) - padoffset

switch (side) {
case "left":
Expand Down Expand Up @@ -129,6 +131,7 @@ export const quad = (
p: parameters.p ?? 0.5,
pl: parameters.pl,
legsoutside: parameters.legsoutside,
padoffset: parameters.padoffset,
})

let pw = parameters.pw
Expand Down
2 changes: 1 addition & 1 deletion tests/__snapshots__/qfn16_w4_h4_p0.65mm.snap.svg
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