Heavy-copper PCB

/Heavy-copper PCB
Heavy-copper PCB 2017-09-26T10:43:46+00:00

Current Carrying Capacity and Temperature Rise

The amount of current a copper circuit can safely carry depends on how much heat rise a project can withstand, since heat rise and current flow are related. When current flows along a trace, there is an I2R (power loss) that results in localized heating. The trace cools by conduction (into neighboring materials) and convection (into the environment). Therefore, to find the maximum current a trace can safely carry, we must find a way to estimate the heat rise associated with the applied current. An ideal situation would be to reach a stable operating temperature where the rate of heating equals the rate of cooling. An IPC formula can be used to model this event.

Approximate Current for Given Track Dimensions(20°C temp rise)
Cu weight(oz/ft2) Thickness(inch) Track Width(inch)
0.0625 0.1250 0.2500 0.5000 1.0000 2.0000 4.0000 8.0000 16.0000
1 0.0014 4.6 7.6 12.5 20.7 34.2 56.6 93.6 154.7 255.6
2 0.0028 7.6 12.5 20.7 34.2 56.6 93.6 154.7 255.6 422.5
4 0.0056 12.5 20.7 34.2 56.6 93.6 154.7 255.6 422.5 698.4
6 0.0084 16.8 27.8 46.0 76.0 125.5 207.5 343.0 566.9 937.1
8 0.0112 20.7 34.2 56.6 93.6 154.7 255.6 422.5 698.4 1154.4
10 0.0140 24.4 40.3 66.5 110.0 181.8 300.5 496.7 821.1 1357.1
12 0.0168 27.8 46.0 76.0 125.5 207.5 343.0 566.9 937.1 1548.9
14 0.0196 31.1 51.4 84.9 140.4 232.0 383.6 634.0 1047.9 1732.1
16 0.0224 34.2 56.6 93.6 154.7 255.6 422.5 698.4 1154.4 1908.1
18 0.0252 37.3 61.7 101.9 168.4 278.4 460.2 760.7 1257.3 2078.2
20 0.0280 40.3 66.5 110.0 181.8 300.5 496.7 821.1 1357.1 2243.2
24 0.0336 46.0 76.0 125.5 207.5 343.0 343.0 937.1 1548.9 2560.2
28 0.0392 51.4 84.9 140.4 232.0 383.6 634.0 1047.9 1732.1 2863.0
32 0.0448 56.6 93.6 154.7 255.6 422.5 698.4 1154.4 1908.1 3154.0
36 0.0504 61.7 101.9 168.4 278.4 460.2 760.7 1257.3 2078.2 3435.1
40 0.0560 66.5 110.0 181.8 300.5 496.7 821.1 1357.1 2243.2 3707.8
45 0.0630 72.5 119.8 198.0 327.3 541.0 894.3 1478.1 2443.2 4038.3
50 0.0700 78.2 129.3 213.7 353.3 584.0 965.2 1595.5 2637.1 4358.9
55 0.0770 83.8 138.6 229.0 378.6 625.7 1034.3 1709.6 2825.8 4670.8
60 0.0840  / 147.6 244.0 403.2 666.5 1101.7 1820.9 3009.8 4974.9
70 0.0980  / 165.0 272.8 450.9 745.3 1231.9 2036.2 3365.7 5563.1
80 0.1120  / 181.8 300.5 496.7 821.1 1357.1 2243.2 3707.8 6128.6
90 0.1260  / 198.0 327.3 541.0 894.3 1478.1 2443.2 4038.3 6675.0
100 0.1400  / 213.7 353.3 584.0 965.2 1595.5 2637.1 4358.9 7204.8
120 0.1680  /  / 403.2 666.5 1101.7 1820.9 3009.8 4974.9 8223.0
140 0.1960  /  / 450.9 745.3 1231.9 2036.2 3365.7 5563.1 9195.3
160 0.2240  /  / 496.7 821.1 1357.1 2243.2 3707.8 6128.6 10130.0
180 0.2520  /  / 541.0 894.3 1478.1 2443.2 4038.3 6675.0 11033.1
200 0.2800  /  / 584.0 965.2 1595.5 2637.1 4358.9 7204.8 11908.9

IPC-2221A, calculation for current capacity of an external track [1]:
I = .048 * DT(.44) * (W * Th)(.725)

Where I is current (amps), DT is temperature rise (°C), W is width of the trace (mil) and Th is thickness of the trace (mil). Internal traces should be derated by 50% (estimate) for the same degree of heating. Using the IPC formula, we generated Figure 3 (see table at end of text), showing the current carrying capacity of several traces of differing cross-sectional areas with a 20°C temperature rise.

What constitutes an acceptable amount of heat rise will differ from project to project. Most circuit board dielectric materials can withstand temperatures of 100°C above ambient, although this amount of temperature change would be unacceptable in most situations.