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Add biscuit board laser ablation essentials guide (#306)
* Document biscuit board laser ablation workflow * Streamline laser prefab via documentation * Clarify laser prefab terminology * Trim laser prefab guidance
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‎docs/elements/board.mdx‎

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@@ -86,7 +86,8 @@ Usually you'll want to use an autorouter preset:
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- `autorouter="auto"` - Uses the [platform configuration](../guides/running-tscircuit/platform-configuration.md). For tscircuit.com this defaults to `sequential-trace`.
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- `autorouter="sequential-trace"` - Iterate over each trace and use tscircuit's fast built-in autorouter. This method is fast and deterministic but often fails with over 50 traces.
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- `autorouter="auto-local"` - Use the platform configuration, but only route locally (do not make API calls)
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- `autorouter="auto-cloud"` - Use the platform configuration for
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- `autorouter="auto-cloud"` - Use the platform configuration for
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- `autorouter="laser_prefab"` - Reserve prefabricated vias that can be reassigned during routing. Ideal for rapid-turn PCBs produced with laser ablation and mechanical drilling templates. See the [Biscuit Board Laser Ablation guide](../guides/tscircuit-essentials/biscuit-board-laser-ablation.mdx) for a complete walkthrough.
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For complex boards with over 50 traces, you should use `autorouter="auto-cloud"`
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to take advantage of tscircuit's cloud autorouters, which internally use the popular

‎docs/elements/via.mdx‎

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@@ -42,3 +42,4 @@ import CircuitPreview from "@site/src/components/CircuitPreview"
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| outerDiameter | number \| string | "0.8mm" | Outer diameter of the copper annular ring |
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| pcbX | number | 0 | PCB X position of the via |
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| pcbY | number | 0 | PCB Y position of the via |
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| netIsAssignable | boolean | `false` | Marks the via as prefabricated so autorouters like `laser_prefab` can claim it for any compatible net. For a full workflow, see the [Biscuit Board Laser Ablation guide](../guides/tscircuit-essentials/biscuit-board-laser-ablation.mdx). |

‎docs/guides/tscircuit-essentials/biscuit-board-laser-ablation.mdx‎

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---
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title: Biscuit Board Laser Ablation
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description: Learn how to route PCBs against a prefabricated via template using the laser_prefab autorouter and the netIsAssignable via property.
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---
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import CircuitPreview from "@site/src/components/CircuitPreview"
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# Biscuit Board Laser Ablation
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The **laser_prefab** autorouter pairs tscircuit with a fabrication process that
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combines laser ablation and a "biscuit" carrier board. Fabricators pre-drill a
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matrix of vias into an inexpensive substrate—the biscuit—then laminate thin
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copper to the top and bottom. A UV or IR laser ablates the copper, defining the
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traces while leaving the via barrels intact. Because the vias are prefabricated,
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you route against a known template instead of drilling new holes for every
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board.
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This guide walks through designing for that workflow. You'll learn how to:
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1. Build a reusable via template (the biscuit board).
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2. Place that template, route with `autorouter="laser_prefab"`, and confirm the results match the prefabricated geometry.
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## 1. Build a reusable via template (a biscuit board)
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Create a component for your biscuit template that contains every via location
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available on the board. Mark each via with `netIsAssignable` so it is treated as
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an assignable via when the router runs. The vias can optionally include default
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net names to serve as documentation for repeated layouts.
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```tsx title="src/biscuit-template.tsx"
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import { Fragment } from "react"
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export const BiscuitTemplate = () => (
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<Fragment>
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<via name="B1" pcbX={-4} pcbY={6} fromLayer="top" toLayer="bottom" netIsAssignable />
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<via name="B2" pcbX={0} pcbY={6} fromLayer="top" toLayer="bottom" netIsAssignable />
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<via name="B3" pcbX={4} pcbY={6} fromLayer="top" toLayer="bottom" netIsAssignable />
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<via name="B4" pcbX={-4} pcbY={0} fromLayer="top" toLayer="bottom" netIsAssignable />
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<via name="B5" pcbX={0} pcbY={0} fromLayer="top" toLayer="bottom" netIsAssignable />
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<via name="B6" pcbX={4} pcbY={0} fromLayer="top" toLayer="bottom" netIsAssignable />
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</Fragment>
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)
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```
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Keep the template focused on the vias themselves. Copper features such as
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fiducials or alignment marks should live in their own components so you can swap
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templates without affecting the mechanical stackup.
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## 2. Place the biscuit template, route, and validate
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Include the template inside your `<board />` before adding components. Because
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the vias are already drilled in the physical biscuit, avoid translating or
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rotating the template in a way that misaligns the coordinates.
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<CircuitPreview
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defaultView="pcb"
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code={`export default () => (
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<board width="20mm" height="20mm" autorouter="laser_prefab">
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<group name="biscuit" pcbX={0} pcbY={0}>
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<via name="B1" pcbX={-4} pcbY={6} fromLayer="top" toLayer="bottom" netIsAssignable />
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<via name="B2" pcbX={0} pcbY={6} fromLayer="top" toLayer="bottom" netIsAssignable />
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<via name="B3" pcbX={4} pcbY={6} fromLayer="top" toLayer="bottom" netIsAssignable />
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<via name="B4" pcbX={-4} pcbY={0} fromLayer="top" toLayer="bottom" netIsAssignable />
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<via name="B5" pcbX={0} pcbY={0} fromLayer="top" toLayer="bottom" netIsAssignable />
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<via name="B6" pcbX={4} pcbY={0} fromLayer="top" toLayer="bottom" netIsAssignable />
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</group>
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<testpoint name="TP_TOP" footprintVariant="pad" pcbX={0} pcbY={9} layer="top" />
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<testpoint name="TP_BOTTOM" footprintVariant="pad" pcbX={0} pcbY={-9} layer="bottom" />
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</board>
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)`}
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/>
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Keep the board outline slightly inside the biscuit's usable area so the laser
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can clear debris without hitting the rails.
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Once the template is in place, add traces exactly as you would for a conventional
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board. The router treats assignable vias as neutral territory: any net can claim
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them provided both layers are available and no design rules are violated.
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```tsx title="src/laser-prefab-example.tsx"
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<board width="20mm" height="20mm" autorouter="laser_prefab">
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<BiscuitTemplate />
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<chip
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name="U1"
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footprint="soic8"
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pcbX={-6}
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pcbY={0}
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connections={{ pin1: "R1.pin1", pin8: "B6.top" }}
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/>
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<resistor name="R1" resistance="1k" footprint="0402" pcbX={6} pcbY={0} />
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<trace from="TP_TOP.pin1" to="B2.top" />
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<trace from="B2.bottom" to="TP_BOTTOM.pin1" />
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</board>
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```
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After generating manufacturing data (Gerber or ODB++ exports) or reviewing the
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PCB preview, confirm that:
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- Every claimed via matches a real location on the biscuit template.
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- Unused vias remain isolated and keep their original net names.
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- Trace clearances respect your fabrication limits.
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<CircuitPreview
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defaultView="pcb"
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code={`export default () => (
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<board width="20mm" height="20mm" autorouter="laser_prefab">
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<group name="biscuit">
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<via name="B2" pcbX={0} pcbY={6} fromLayer="top" toLayer="bottom" netIsAssignable />
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<via name="B5" pcbX={0} pcbY={0} fromLayer="top" toLayer="bottom" netIsAssignable />
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</group>
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<testpoint name="TP_TOP" footprintVariant="pad" pcbX={0} pcbY={9} layer="top" />
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<testpoint name="TP_BOTTOM" footprintVariant="pad" pcbX={0} pcbY={-9} layer="bottom" />
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<trace from="TP_TOP.pin1" to="B2.top" />
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<trace from="B2.bottom" to="B5.top" />
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<trace from="B5.bottom" to="TP_BOTTOM.pin1" />
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</board>
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)`}
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/>

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