工具說明

走線寬度是設計人員指定的一項要求，以確保走線能夠處理所需的電流容量。該工具根據以下設計規范計算走線寬度。Trace width is a requirement that designers specify to ensure that the trace can handle the required current capacity. This tool calculates the trace width based upon the following design specifications:

• 最大電流Max Current
• 跡線厚度Trace Thickness
• 最大期望溫升Max Desired Temperature Rise

此工具還計算與跟蹤相關的以下附加有價值信息。This tool also calculates the following additional valuable information related to the trace:

• 阻抗Resistance
• 壓降Voltage Drop
• 線寬功耗Trace Power Dissipation

說明

該工具基于標準文檔 [1] 中包含的公式和圖表，計算傳導給定電流所需的銅印刷電路板走線的厚度，同時保持走線本身的溫升低于指定的輸入值。

通過提供額外的輸入參數（環境溫度和走線長度），可以計算走線總溫度、電阻、電壓降和功耗（功率損耗）。

應該注意的是，由于通過空氣對流散熱，外部 PCB 層比內部層實現更好的熱傳遞。反過來說，內部電介質不能很好地導熱，這就解釋了為什么內部走線比外部走線寬。

This tool, based on the formulas and graphs contained in the standard document [1], calculates the thickness of a copper printed circuit board trace required to conduct a given current, keeping the temperature increase of the trace itself below the specified input value.

By providing additional input parameters (ambient temperature and trace length), it is possible to calculate the trace total temperature, resistance, voltage drop and power dissipation (power loss).

It should be noted that external PCB layers achieve better heat transfer than internal layers, due to the heat dissipation through air convection. The other way around, internal dielectric does not conduct heat very well and that explains why internal traces are wider than external traces.

線寬計算

First, calculate the area according to the following formula:

A = (I / (k * T_RISE^b))^1/c                                     (I)

Then, calculate the trace width:

W = A / (T * 1.378 [mils/oz/ft²])                 (II)

Where:

A is the cross-section area [mils²], I is the maximum current [A], T_RISE is the maximum desired temperature rise [°C], W is the trace width [mils], T is the trace thickness [oz/ft²], k, b and c are constants. According to IPC-2221A Par. 6.2 (“Conductive Material Requirements”), their values for inner layers are as follows: k = 0.048 b = 0.44 c = 0.725

Equation (II) is based on a curve fit to the charts provided in [1] (par. 6.2, Figure B and Figure C).

Trace temperature calculation

The overall trace temperature can be calculated as follows

T_TEMP = T_RISE + T_AMB

Where:

T_TEMP is the trace temperature [°C], T_RISE is the maximum desired temperature rise [°C], T_AMB is the ambient temperature [°C].

Resistance calculation

First, convert the cross-section area from [mils²] to [cm²]:

A’ = A * 2.54 * 2.54 * 10^-6

Then, calculate the resistance:

R = (ρ * L / A’) * (1 + α * (T_TEMP – 25 °C))

Where:

T is the trace thickness [oz/ft²], W is the trace width [mils], R is the resistance [Ω], ρ is the resistivity parameter, whose value for copper is 1.7E-6 [Ω · cm], L is the trace length [cm], α is the resistivity temperature coefficient, whose value for copper is 3.9E-3 [1/°C], T_TEMP is the trace temperature [°C]

Voltage drop calculation

Voltage drop can be calculated as follows:

V_DROP = I * R

Where:

V_DROP is the voltage drop [V] I is the maximum current [A] R is the resistance [Ω]

Power dissipation calculation

Power dissipation, or power loss, can be calculated according to the following formula:

P_LOSS = R * I²

Where: P_LOSS is the power loss [W], R is the resistance [Ω], I is the maximum current [A]

Example 1

Inputs

I = 10 A

T = 2 mil

T_RISE = 20 °C

T_AMB = 25 °C

L = 10 inch

Output

Cross-section Area = 256.27 mils²

Trace Width = 128.13 mil

Additional output

Trace Temperature = 45 °C

Resistance = 0.0282 Ω

Voltage Drop = 0.282 V

Power Dissipation = 2.82 W

Example 2

Inputs

I = 8 A

T = 3 oz/ft²

T_RISE = 86 °F

T_AMB = 27 °C

L = 10 inch

Output

Cross-section Area = 147.29 mils²

Trace Width = 35.63 mil

Additional output

Trace Temperature = 57 °C

Resistance = 0.0511 Ω

Voltage Drop = 0.409 V

Power Dissipation = 3.27 

Reference

[1] IPC-2221A “Generic Standard on Printed Board Design” 

[2] https://www.omnicalculator.com 

[3] https://www.omnicalculator.com/all/pcb-trace-width