fix: extend BGA row labels beyond Z with double letters (AA, AB, ...)

src/fn/bga.ts

@@ -5,7 +5,7 @@ import type {
 } from "circuit-json"
 import { rectpad } from "../helpers/rectpad"
 import { circlepad } from "../helpers/circlepad"
-import { ALPHABET } from "../helpers/zod/ALPHABET"
+import { ALPHABET, bgaRowLabel } from "../helpers/zod/ALPHABET"
 import { z } from "zod"
 import { base_def } from "../helpers/zod/base_def"
 import { length, distance } from "circuit-json"
@@ -153,8 +153,7 @@ export const bga = (
       }
       pin_num -= missing_pins_passed
 
-      // TODO handle >26 rows
-      const portHints = [pin_num, `${ALPHABET[pin_y]}${pin_x + 1}`]
+      const portHints = [pin_num, `${bgaRowLabel(pin_y)}${pin_x + 1}`]
       pads.push(
         parameters.circularpads
           ? circlepad(portHints, {

src/helpers/zod/ALPHABET.ts

@@ -1 +1,23 @@
 export const ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+
+/**
+ * Return a row label for a zero-based row index, extending beyond Z
+ * with double letters (AA, AB, …, AZ, BA, …).
+ *
+ *   Rows  0–25  → A … Z   (single letter, same as ALPHABET)
+ *   Rows 26–51  → AA … AZ
+ *   Rows 52–77  → BA … BZ
+ *   … and so on.
+ *
+ * This keeps backwards compatibility with the existing A–Z labeling
+ * while supporting large BGA packages (>26 rows).
+ */
+export function bgaRowLabel(row: number): string {
+  if (row < 26) {
+    return ALPHABET[row]!
+  }
+
+  const groupIndex = Math.floor((row - 26) / 26)
+  const letterIndex = (row - 26) % 26
+  return `${ALPHABET[groupIndex]}${ALPHABET[letterIndex]}`
+}

tests/bga-large-grid-row-labels.test.ts

@@ -0,0 +1,40 @@
+import { test, expect } from "bun:test"
+import type { PcbSmtPad } from "circuit-json"
+import { convertCircuitJsonToPcbSvg } from "circuit-to-svg"
+import { fp } from "../src/footprinter"
+
+test("bga 30x30 grid has valid row labels beyond Z", () => {
+  const soup = fp.string("bga900_grid30x30_p0.5").circuitJson()
+  const pads = soup.filter((el): el is PcbSmtPad => el.type === "pcb_smtpad")
+
+  expect(pads).toHaveLength(900)
+
+  // No pad should have "undefined" in its label
+  for (const pad of pads) {
+    expect(pad.port_hints?.[1]).not.toContain("undefined")
+  }
+
+  // Row 0 = A, Row 25 = Z (single letters)
+  const pinA1 = pads.find((p) => p.port_hints?.[0] === "1")
+  expect(pinA1?.port_hints?.[1]).toBe("A1")
+
+  const pinZ1 = pads.find((p) => p.port_hints?.[1] === "Z1")
+  expect(pinZ1).toBeDefined()
+
+  // Row 26 = AA, Row 27 = AB (double letters)
+  const pinAA1 = pads.find((p) => p.port_hints?.[1] === "AA1")
+  expect(pinAA1).toBeDefined()
+
+  const pinAB1 = pads.find((p) => p.port_hints?.[1] === "AB1")
+  expect(pinAB1).toBeDefined()
+
+  // Row 29 = AD (last row of a 30x30 grid)
+  const pinAD1 = pads.find((p) => p.port_hints?.[1] === "AD1")
+  expect(pinAD1).toBeDefined()
+
+  const svgContent = convertCircuitJsonToPcbSvg(soup)
+  expect(svgContent).toMatchSvgSnapshot(
+    import.meta.path,
+    "bga_30x30_large_grid",
+  )
+})

tests/bga-row-label-helper.test.ts

@@ -0,0 +1,8 @@
+import { test, expect } from "bun:test"
+import { bgaRowLabel, ALPHABET } from "../src/helpers/zod/ALPHABET"
+
+test("bgaRowLabel matches ALPHABET for rows 0-25", () => {
+  for (let i = 0; i < 26; i++) {
+    expect(bgaRowLabel(i)).toBe(ALPHABET[i])
+  }
+})

tests/bga-row-label-helper2.test.ts

@@ -0,0 +1,11 @@
+import { test, expect } from "bun:test"
+import { bgaRowLabel } from "../src/helpers/zod/ALPHABET"
+
+test("bgaRowLabel produces double letters after Z", () => {
+  expect(bgaRowLabel(26)).toBe("AA")
+  expect(bgaRowLabel(27)).toBe("AB")
+  expect(bgaRowLabel(51)).toBe("AZ")
+  expect(bgaRowLabel(52)).toBe("BA")
+  expect(bgaRowLabel(77)).toBe("BZ")
+  expect(bgaRowLabel(78)).toBe("CA")
+})