Internal Trace Width Calculator (PCB)

Tools介紹
Based on the charts found in IPC-2221, this tool calculates the width of an internal trace necessary to carry the specified current. Also calculated are the trace's temperature, resistance, voltage drop, and power dissipation.
PCB Trace Width Calculator

Description

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). Trace Width calculation First, calculate the area according to the following formula:

A = (I / (k * TRISEb))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], TRISE 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 = 0.024 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

TTEMP = TRISE + TAMB

Where:

TTEMP is the trace temperature [°C], TRISE is the maximum desired temperature rise [°C], TAMB 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 * (TTEMP – 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], TTEMP is the trace temperature [°C].

Voltage drop calculation

Voltage drop can be calculated as follows:

VDROP = I * R

Where:

VDROP 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:

PLOSS = R * I2

Where:

PLOSS is the power loss [W]

R is the resistance [Ω]

I is the maximum current [A]

Example 1

Inputs

I = 5 A
T = 4 oz/ft2
TRISE = 15 °C
TAMB = 27 °C
L = 12 cm

Output

Cross-section Area = 305.16 mils2
Trace Width = 55.36 mil

Trace Temperature = 42 °C
Resistance = 0.011 Ω
Voltage Drop = 0.055 V
Power Dissipation = 0.275 W

Example 2

Inputs

I = 10 A
T = 2 mil
TRISE = 50 °F
TAMB = 22 °C
L = 5 inch

Output

Cross-section Area = 1015.33 mils2
Trace Width = 507.65 mil

Trace Temperature = 32 °C
Resistance = 0.0034 Ω
Voltage Drop = 0.034 V
Power Dissipation = 0.34 W

Reference

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