PCB 走线宽度计算器

PCB 走线宽度计算器用于确定安全承载给定电流而不超过温度限制所需的最小铜走线宽度。输入电流负载、允许温升、铜厚（oz）和层面类型（外层或内层），使用 IPC-2221 标准公式获取以 mil 和毫米为单位的最小走线宽度。

PCB Trace Width Calculator

Calculate minimum PCB trace width using the IPC-2221 standard for external and internal copper layers.

External layers have better heat dissipation (k = 0.048).

Maximum continuous current the trace must carry.

Allowable temperature rise above ambient. IPC-2221 typically recommends 10°C for most designs.

Standard PCB copper weights: 0.5 oz = 17.5 µm, 1 oz = 35 µm, 2 oz = 70 µm.

Frequently Asked Questions

PCB走线宽度的IPC-2221标准是什么？

IPC-2221是印制板设计通用标准，提供了基于电流、铜厚和温升的走线宽度计算方法。内层走线：W = (I / (k × ΔT^b))^(1/c) / T^d；外层类似但系数不同。其中k、b、c、d是经验系数，ΔT为允许温升（°C），T为铜箔厚度（盎司/平方英尺）。

如何计算PCB走线宽度？

简化步骤：1. 确定走线电流（A）；2. 确定铜厚（常见1oz = 35μm，2oz = 70μm）；3. 确定允许温升（通常10°C内层，20°C外层）；4. 使用IPC-2221公式或计算器。经验法则：1oz铜，10°C温升，外层1A约需0.4mm走线宽度；每增加1A约需增加0.3-0.5mm宽度。

内层和外层走线宽度有何不同？

外层（暴露在空气中）散热好，相同电流所需走线更窄；内层（被FR4包夹）散热差，相同电流需要约1.5-2倍宽度。IPC-2221对内外层使用不同系数：外层 k=0.048, b=0.44, c=0.725；内层 k=0.024, b=0.44, c=0.725（单位制需注意）。

什么是铜箔厚度（oz/ft²），如何换算？

铜箔厚度以盎司/平方英尺（oz/ft²）表示：1oz = 35μm（1.38mil）；2oz = 70μm（2.76mil）；0.5oz = 17.5μm；3oz = 105μm。标准PCB默认1oz，电源板通常用2oz；大电流场合（>10A）可用4oz甚至更厚铜。更厚铜意味着相同走线宽度能承载更大电流，但成本更高。

PCB走线阻抗如何影响高速信号？

高速PCB设计（USB、HDMI、以太网等）需要控制走线特性阻抗（通常50Ω单端或100Ω差分）。走线阻抗由走线宽度、铜厚、介质层厚度和介电常数决定。阻抗不匹配会造成信号反射、完整性问题和EMI辐射。高速走线宽度必须用阻抗计算器专门计算，而非仅考虑电流承载能力。

PCB走线的电阻如何计算？

走线电阻 R = ρ × L / (W × T)，其中ρ为铜的电阻率（1.72×10⁻⁸ Ω·m）、L为走线长度、W为宽度、T为铜厚。在20°C时，每平方的1oz铜电阻约500mΩ/sq（方块电阻）。例如10cm长、1mm宽的1oz铜走线：R ≈ 500×10⁻³ × 100/1 = 50mΩ。

PCB走线设计有哪些常见规则？

常见PCB走线设计规则：信号线最小宽度0.1mm（6mil），推荐0.15-0.2mm；电源线根据电流确定宽度；走线间距≥走线宽度（差分对间距更严格）；高速差分线等长等宽；电源与地平面之间保持完整性；避免走线锐角（使用45°或圆角）；Via孔直径≥0.3mm，焊盘直径≥Via+0.5mm。

如何验证PCB走线宽度是否合适？

验证方法：使用本计算器确认理论宽度；在PCB设计软件中设置DRC（设计规则检查）规则；评估温升（热仿真软件）；必要时实物测试（用热成像仪检查实际温升）。建议在计算值基础上增加20-50%余量，长期可靠性更有保障。大电流走线（>5A）建议每隔5cm添加过孔散热或使用铜块加强。

PCB Trace Width Calculator: IPC-2221 Current Capacity Guide

The PCB Trace Width Calculator determines the minimum copper trace width required to safely carry a given current without exceeding an allowable temperature rise. It implements the IPC-2221 standard — the industry reference for printed circuit board design — and supports both external (outer) and internal (inner) copper layers with standard 0.5 oz, 1 oz, and 2 oz copper weights.

Table of Contents

IPC-2221 Formula

The IPC-2221 standard defines the empirical relationship between current, temperature rise, and cross-section area for PCB copper traces. The formula is derived from curve-fit data across a wide range of trace sizes and current loads.

Current Capacity Formula:

I = k × ΔT0.44 × A0.725

Solved for cross-section area:

A = (I / (k × ΔT0.44))1/0.725

Trace width from area:

Width (mils) = A (mils²) / thickness (mils)
  • I — current in amperes (A)
  • ΔT — allowable temperature rise above ambient in °C
  • A — cross-section area in mils²
  • k — 0.048 for external layers, 0.024 for internal layers
  • 1 mil = 0.001 inch = 0.0254 mm

Copper thickness conversion:

thickness (mils) = weight (oz/ft²) × 1.378

Note: The IPC-2221 formula is empirical and was curve-fitted from older data. It is widely used as a conservative starting point. For high-reliability designs, IPC-2152 provides updated charts based on more modern test data with thermal substrate effects included.

Internal vs External Layers

The IPC-2221 standard defines different k factors for external and internal copper layers because their heat dissipation characteristics differ significantly:

Layer Typek FactorHeat DissipationRelative Trace Width
External (Outer)0.048Good — exposed to air or solder maskNarrower
Internal (Inner)0.024Poor — surrounded by FR4 laminate~2× Wider

The k factor for internal layers is exactly half that of external layers, meaning for the same current and temperature rise, an internal trace will be approximately twice as wide as an external trace. This is because FR4 substrate is a poor thermal conductor (thermal conductivity ~0.3 W/m·K vs air at 0.026 W/m·K), so heat cannot escape as effectively.

Design Practice: Route high-current traces (power rails, motor drives, battery connections) on external layers whenever possible. If an internal layer must carry significant current, apply a generous derating factor and consider using thicker copper (2 oz or more).

Copper Thickness Guide

PCB copper weight is specified in ounces per square foot (oz/ft²). Standard copper weights and their physical thicknesses:

Copper WeightThickness (mils)Thickness (µm)Typical Use
0.5 oz0.68917.5 µmFine-pitch signal traces, high-density boards
1 oz1.37835 µmGeneral purpose — most common PCB standard
2 oz2.75670 µmPower electronics, high-current boards
3 oz4.134105 µmHeavy power boards, bus bars
4 oz5.512140 µmExtreme current applications

1 oz/ft² copper = 1.378 mils = 34.98 µm thickness. Standard PCBs use 1 oz copper on outer layers and may use 0.5 oz on inner layers for finer etching.

How to Use the PCB Trace Width Calculator

  1. Select layer type — choose External for top/bottom copper layers, Internal for inner layers in multilayer boards.
  2. Enter current — the maximum continuous DC current (in amperes) the trace must carry.
  3. Set temperature rise — the allowable rise above ambient. 10°C is the IPC-2221 recommendation for most designs; use 20°C–40°C for relaxed thermal requirements.
  4. Choose copper thickness — use the presets (0.5 oz / 1 oz / 2 oz) or type a custom value. Standard boards use 1 oz.
  5. Click Calculate — view the minimum trace width in mils and millimeters, plus cross-section area.

Design Tips

1. Add a Safety Margin

The IPC-2221 result is the minimum width. In practice, add 20–50% extra width for margin. If the calculator returns 15 mils, use 20–22 mils. This accounts for manufacturing tolerances, acid etching variation, and real-world ambient temperature variation.

2. Use Thicker Copper for Power Traces

Doubling copper thickness (from 1 oz to 2 oz) roughly halves the required trace width for the same current. This is especially valuable in dense boards where space is limited. Note: thicker copper increases etching difficulty and cost.

3. Consider Via Current Capacity

When routing high-current traces between layers, vias are often the bottleneck. A single standard via (0.3 mm drill, 1 oz copper) typically handles only 0.5–1 A. Use multiple vias in parallel or larger via annular rings for high-current transitions.

4. Temperature Rise Selection

IPC-2221 recommends 10°C rise for most consumer designs. For boards in enclosures with poor ventilation, use 5°C or less. For boards with excellent airflow or in automotive/industrial applications with higher ambient temps, calculate the actual allowable rise: ΔT = T_max_component − T_ambient_max.

5. Ground and Power Planes

For very high currents (10 A+), consider using a full copper pour (power plane or polygon fill) instead of a narrow trace. Planes have effectively zero resistance along their width and provide much better current distribution and thermal management.

Worked Examples

Example 1: USB Power Trace (5 V, 0.5 A, 1 oz, External)

  1. k = 0.048 (external), ΔT = 10°C, I = 0.5 A
  2. A = (0.5 / (0.048 × 100.44))1/0.725 ≈ 3.6 mils²
  3. Thickness = 1 × 1.378 = 1.378 mils
  4. Width = 3.6 / 1.378 ≈ 2.6 mils (0.066 mm)
  5. With 50% margin: use 4 mils minimum — well within standard 6 mil minimum trace capability

Example 2: Motor Driver Power Rail (5 A, 10°C, 1 oz, External)

  1. k = 0.048 (external), ΔT = 10°C, I = 5 A
  2. A = (5 / (0.048 × 100.44))1/0.725 ≈ 83 mils²
  3. Thickness = 1 × 1.378 = 1.378 mils
  4. Width = 83 / 1.378 ≈ 60 mils (1.52 mm)
  5. With 25% margin: use 75 mils (1.9 mm)

Example 3: Internal Layer Power Bus (3 A, 10°C, 2 oz, Internal)

  1. k = 0.024 (internal), ΔT = 10°C, I = 3 A
  2. A = (3 / (0.024 × 100.44))1/0.725 ≈ 85 mils²
  3. Thickness = 2 × 1.378 = 2.756 mils
  4. Width = 85 / 2.756 ≈ 31 mils (0.79 mm)
  5. Compare: same current on external 1 oz layer would only need ~30 mils — internal 2 oz is roughly equivalent