Design Rules Reference

Generic engineering reference lookups: trace-width/current-capacity, electrical clearance, protocol routing, decoupling, and a static DFM checklist.

Overview

The design-rules module is a knowledge pack, not a design tool: every lookup returns a source and a caveat alongside the computed or looked-up value. These are widely-published engineering rules of thumb — not certified values, not a replacement for the actual standard, your fabricator's capability table, or the target IC's datasheet.

This is exposed to agents through a single MCP tool, easyeda_design_rules_lookup, discriminated by a topic field:

Topic	Purpose
trace-width	IPC-2221 minimum conductor width for a required current/temperature rise
max-current	IPC-2221 maximum current for a given trace width (reverse lookup)
clearance	Simplified, conservative voltage-based electrical clearance bands
protocol-routing	Routing reference data: USB 2.0/3.x, RS-485, I2C, SPI, UART, Ethernet
decoupling	Per-pin decoupling capacitor recipes by IC category
bulk-capacitance	Rail bulk capacitance sizing (shares the power-tree analyzer's rule)
dfm-checklist	Static, generic design-for-manufacturability checklist

Trace width / current capacity

src/design-rules/trace-width.ts implements the IPC-2221 (formerly MIL-STD-275) empirical curve:

I = k · ΔT^0.44 · A^0.725

where I is current in amps, ΔT is the allowed temperature rise in °C, A is cross-sectional area in mils², and k is 0.048 for external (outer layer) conductors or 0.024 for internal conductors.

import { calculateTraceWidth, calculateMaxCurrent } from './design-rules/trace-width.js';

calculateTraceWidth({
  currentA: 2,
  temperatureRiseC: 10,
  layer: 'external',
  copperWeightOz: 1,
});
// → { traceWidthMils, traceWidthMm, requiredAreaMils2, copperThicknessMils, k, source, caveat }

calculateMaxCurrent({
  traceWidthMils: 20,
  temperatureRiseC: 10,
  layer: 'external',
  copperWeightOz: 1,
});
// → { maxCurrentA, source, caveat }

This is an estimate: it does not model adjacent-trace heating, via/plane proximity, forced airflow, or altitude. IPC-2152 supersedes IPC-2221 with more conservative guidance for dense modern boards — cross-check for safety-critical or high-reliability current paths.

Electrical clearance

src/design-rules/clearance.ts provides deliberately coarse, safety-margined clearance bands loosely modeled on IPC-2221's "clearance grows with voltage" shape — not a reproduction of the exact IPC-2221 Table 6-1 through 6-4 breakpoints. Internal clearances are always set at least as large as external for the same band, so the estimate never under-recommends.

import { lookupClearance } from './design-rules/clearance.js';

lookupClearance({ voltageV: 48, location: 'external' });
// → { minClearanceMm, minClearanceMils, bandMaxVoltageV, source, caveat }

Voltages above the covered range (>500V) return outOfRange: true and point to IPC-2221's high-voltage guidance and applicable safety standards instead of extrapolating a floor value. Always consult the actual IPC-2221 tables or your fabricator's certified minimums before finalizing a safety-critical or mains-adjacent clearance.

Protocol routing

src/design-rules/protocol-routing.ts covers USB 2.0, USB 3.x, RS-485, I2C, SPI, UART, and 10/100/1000BASE-T Ethernet: topology, differential impedance, termination, pull-up ranges, and length-matching guidance, each citing the governing spec (USB-IF, TIA/EIA-485, NXP UM10204, IEEE 802.3).

import { lookupProtocolRouting, listProtocolRoutingKeys } from './design-rules/protocol-routing.js';

lookupProtocolRouting('rs485');
// → { protocol, displayName, topology, terminationOhms: 120, ... }

listProtocolRoutingKeys();
// → ['usb2', 'usb3', 'rs485', 'i2c', 'spi', 'uart', 'ethernet-10-100', 'ethernet-1000']

Decoupling

src/design-rules/decoupling.ts gives per-pin decoupling recipes by IC category (digital-logic, mcu, analog, rf, crystal-oscillator, power-regulator), plus rail-level bulk capacitance sizing that reuses the exact same rule as the power-tree analyzer (47µF per amp, 10µF floor) so the two never disagree.

import { lookupDecouplingGuidance, recommendBulkCapacitance } from './design-rules/decoupling.js';

lookupDecouplingGuidance('mcu');
// → { category, displayName, perPinCapacitorsNf, placement, notes, source, caveat }

recommendBulkCapacitance(1.5);
// → { requiredBulkCapacitanceUf, loadA, source, caveat }

DFM checklist

src/design-rules/dfm-checklist.ts is a fixed, project-independent checklist of manufacturability considerations (trace/space, drilling, solder mask, silkscreen, panelization, assembly). Unlike src/production-qa/generator.ts, which generates a project-specific checklist from real board inputs, this is static reference data.

import { listDfmChecklist, getDfmChecklistItem } from './design-rules/dfm-checklist.js';

listDfmChecklist('drilling');
getDfmChecklistItem('annular-ring');

MCP Tool

easyeda_design_rules_lookup (group design-rules, profile core, read-only, no confirmWrite) exposes all six topics through one discriminated-union input. Example call:

{
  "topic": "trace-width",
  "currentA": 2,
  "temperatureRiseC": 10,
  "layer": "external",
  "copperWeightOz": 1
}

MCP Resources & Prompts

• easyeda://design-rules/reference — markdown overview of available topics
• easyeda://design-rules/dfm-checklist — the full static DFM checklist as JSON
• review_layout prompt — walks an agent through PCB constraint checks, production review, and the relevant design-rules lookups before layout sign-off

File Structure

src/design-rules/
├── trace-width.ts       — IPC-2221 trace-width/current-capacity calculator
├── clearance.ts         — Simplified electrical clearance bands
├── protocol-routing.ts  — USB/RS-485/I2C/SPI/UART/Ethernet reference data
├── decoupling.ts        — Per-pin decoupling recipes + bulk capacitance sizing
├── dfm-checklist.ts     — Static DFM reference checklist
└── index.ts             — Barrel exports

tests/unit/design-rules/
├── trace-width.test.ts
├── clearance.test.ts
├── protocol-routing.test.ts
├── decoupling.test.ts
└── dfm-checklist.test.ts