ESP32 PCB Layout and Routing

Overview

In this tutorial, we will take the reference schematic from the ESP32 development circuit and lay out its components on a physical 2-layer PCB.

Laying out a high-frequency RF microcontroller like the ESP32 requires careful component placement to ensure signal integrity, low noise, and good wireless performance.

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📐 PCB Layout Best Practices

When laying out the ESP32 board, follow these key hardware design rules:

1. Decoupling Capacitors: Place decoupling capacitors (like C4, C9, C19) as close as physically possible to their respective VDD pins on the ESP32.
2. Crystal Oscillator: Keep the crystal (U1) and its load capacitors (C1, C2) very close to the ESP32 XTAL_P/XTAL_N pins. Keep trace lengths short and symmetrical.
3. Antenna Placement: Place the antenna (ANT1) at the outer edge of the PCB. Ensure there is a keepout area (no copper ground plane) underneath and around the antenna to prevent signal attenuation.

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🛠️ Step-by-Step PCB Layout

We will wrap our circuit in a <board> component with a specified size (50mm by 40mm) and position each component using pcbX, pcbY, and pcbRotation.

ESP32PcbLayout.tsx

import React from "react"
import { useESP32_D0WD } from "@tsci/AnasSarkiz.ESP32_D0WD"
import { useResistor, useCapacitor } from "@tscircuit/core"

export const ESP32PcbLayout = () => {
  const ESP32 = useESP32_D0WD("U2")

  // Capacitors with footprints and PCB placement
  const C1 = useCapacitor("C1", { capacitance: "10pF", footprint: "0402", pcbX: -6, pcbY: 12 })
  const C2 = useCapacitor("C2", { capacitance: "10pF", footprint: "0402", pcbX: -10, pcbY: 12 })
  const C3 = useCapacitor("C3", { capacitance: "100pF", footprint: "0402", pcbX: -8, pcbY: 8 })
  const C4 = useCapacitor("C4", { capacitance: "0.1uF", footprint: "0402", pcbX: 5, pcbY: 5 })
  const C5 = useCapacitor("C5", { capacitance: "10nF", footprint: "0402", pcbX: -2, pcbY: 5 })
  const C6 = useCapacitor("C6", { capacitance: "3.3nF", footprint: "0402", pcbX: -2, pcbY: 3 })
  const C9 = useCapacitor("C9", { capacitance: "1nF", footprint: "0402", pcbX: -5, pcbY: -5 })
  const C10 = useCapacitor("C10", { capacitance: "0.1uF", footprint: "0402", pcbX: -10, pcbY: -5 })
  const C11 = useCapacitor("C11", { capacitance: "1uF", footprint: "0402", pcbX: -12, pcbY: -5 })
  const C13 = useCapacitor("C13", { capacitance: "10uF", footprint: "0603", pcbX: -14, pcbY: -5 })

  // Resistors with footprints and PCB placement
  const R1 = useResistor("R1", { resistance: "20k", footprint: "0402", pcbX: -2, pcbY: 1 })
  const R2 = useResistor("R2", { resistance: "0Ω", footprint: "0402", pcbX: -4, pcbY: 10 })
  const R3 = useResistor("R3", { resistance: "499Ω", footprint: "0402", pcbX: 8, pcbY: 8 })
  const R4 = useResistor("R4", { resistance: "2k", footprint: "0402", pcbX: 8, pcbY: -5 })

  return (
    <board width="50mm" height="40mm">
      {/* Main ESP32 Microcontroller positioned at the center */}
      <ESP32 pcbX={0} pcbY={0} />

      {/* Crystal Oscillator close to XTAL pins */}
      <chip
        name="U1"
        manufacturerPartNumber="40MHz-Crystal"
        footprint="crystal_smd_3225"
        pcbX={-8}
        pcbY={15}
        schPortArrangement={{
          topSide: { pins: ["pin1", "pin2"] },
          bottomSide: { pins: ["pin3", "pin4"] }
        }}
      />

      {/* Flash Memory */}
      <chip
        name="U3"
        manufacturerPartNumber="W25Q32"
        footprint="soic8"
        pcbX={12}
        pcbY={6}
      />

      {/* PSRAM Memory */}
      <chip
        name="U4"
        manufacturerPartNumber="LY68L6400"
        footprint="sop8"
        pcbX={12}
        pcbY={-6}
      />

      {/* Antenna at the board edge with ground clearance */}
      <chip
        name="ANT1"
        manufacturerPartNumber="ANT-2.4GHz"
        footprint="antenna_smd_pin"
        pcbX={-20}
        pcbY={-12}
      />

      {/* Schematic placements and connections */}
      {/* ... (Traces and connections mapped from the schematic tutorial) */}
      <trace from=".U2 .pin3" to=".U2 .pin4" />
      <trace from=".U1 .pin1" to=".R2 .pin2" />
      <trace from=".R2 .pin1" to=".U2 .XTAL_P" />
      <trace from=".U1 .pin3" to=".U2 .XTAL_N" />
      
      {/* Decoupling cap routes */}
      <trace from=".C4 .pos" to=".U2 .VDD3P3_CPU" />
      <trace from=".C4 .neg" to="net.GND" />
      
      {/* RF Trace from ESP32 to Antenna matching network */}
      <trace from=".U2 .LNA_IN" to=".ANT1 .pin1" />
    </board>
  )
}

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📡 Routing RF Traces

Traces carrying high-frequency RF signals (like the path from LNA_IN to ANT1) require specialized design parameters:

• Impedance Matching: The trace width must be designed to have a characteristic impedance of 50 $\Omega$. In TSCircuit, you can configure targeted width rules:

  <trace from=".U2 .LNA_IN" to=".ANT1 .pin1" width="0.5mm" />

• Minimize Vias: Avoid placing vias on the RF trace to prevent impedance mismatches and signal reflections. Keep the path as straight as possible.

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Conclusion

With the component placement coordinated and board constraints defined, the TSCircuit autorouter automatically routes the signals using a 2-layer stackup. Make sure to compile the design and verify that the copper clearance around ANT1 is completely empty.