January 19th, 2021
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Trace Width, Current Capacity and Temperature Rise Calculator
This is a three-in-one calculator. Of the three parameters – trace width, maximum allowed temperature rise above the ambient and maximum current capacity of the trace – if any two are known, the tool calculates the third. In addition, it also calculates the DC resistance and the voltage drop across the trace of a given length.
What can you expect from Sierra’s trace width calculator?
For high-current PCBs, the trace width calculation is critical. Hence, we need to know how much trace width is enough to carry that high current. If trace width is not sufficient, then the trace may burn out, impacting the PCB functionality.
Sierra’s trace width calculator tool not only gives you the trace width but also the amount of trace current and the temperature rise. You can alter any of these two parameters to find out the third one for a given trace thickness. This is the only tool that gives you this advantage, and it is also based on the latest IPC-2152 standard.
Yes, Sierra’s trace width calculator is based on the latest IPC-2152 standard!
The IPC 2152 talks about how the temperature rises in various internal and external PCB traces as a result of current being passed through them. It gives the results in graphical format, and the basic idea was to study those graphs and put them into some curve fitting formulas for better understanding. Our tool is developed based on such formulas.
The surprising thing that has come from this standard is that the internal traces are also capable of carrying higher currents close to those of the external traces.
Default tool parameters
The default parameters of this tool are trace length and the ambient temperature, which are kept at values of 1-inch and 25 degrees Celsius, respectively. However, these can be changed as required. The trace length and ambient temperature input fields on the calculator are used to enter the trace length and ambient temperature, respectively.
Our trace width tool also lets you switch between different units as per your convenience.
The units of temperature can be selected as degrees Celsius or Fahrenheit.
The units for length can be chosen as inches, mils, micrometers, millimeters, centimeters, or meters.
The input field has a feature where the user can use the desired units, which provides flexibility.
Why should you choose this trace width calculator?
Essentially there are four main parameters to be considered while designing traces on a PCB:
Trace width (W)
Maximum trace current (Imax)
Rise in the temperature (ΔT)
Trace thickness (Th)
As mentioned previously, if the Imax and ΔT are known then the trace width can be calculated for both internal and external layer traces.
The other parameters required by this tool are ambient temperature (Ta) and trace length (L). This trace width calculator also calculates additional parameters such as resistance of the trace at ambient temperature, the resistance of trace at high temperature (Ta + ΔT), maximum voltage drop, and maximum power loss for a given trace length.
How does the tool work?
We now take you through some examples to make you understand how our tool works. First, we will select the layer (internal/external) for which we are doing the calculations.
1. How is the current calculated?
Enter the trace length (It is the length of the trace/conductor running on the PCB). By default, it is 1-inch for standard PCBs. But for bigger PCBs, it may be higher than this.
The second parameter is the ambient temperature which is 25 ⁰C (by default). You can also change it to ⁰F.
Next, enter 1oz as copper thickness. You can change the unit to mil/mm, etc. as per your preference.
Now, enter the temperature rise value (for a good design, a temperature rise of 20 or 30 ⁰C is acceptable).
Enter the trace width (20 mils).
Click on the ‘Calculate’ button next to the maximum current tab. It will give you the maximum current a trace can handle.
In the same way, you can also calculate for the internal layers.
From the above example, we have calculated:
For external layers, a trace can handle up to 2A of current.
For internal layers, a trace can handle up to 1.90A of current.
If you see the right side of the image given below, you will observe that the trace length is not really involved in the above calculation. The trace length is important when resistance, voltage drop, and power loss need to be calculated at the maximum current.
Let us take another example. For internal layers keeping the previous values intact, if we change the trace width to 10, the trace current is 1.28A. We can see that it is not a linear function because after changing the trace width from 20 to 10, the current does not become half of the earlier value which was 1.90A.
Now, let us increase the trace thickness to 2oz. It gives the trace current of 1.90A.
Note: Keep the parameter box empty which you want to calculate.
2. How is the PCB trace width calculated?
For internal layers, keeping the trace thickness to 1oz, let us say we want to pass a current of 5A. So, how much trace width will it require? It is around 107.285mil.
3. How is the temperature rise calculated?
Similarly, the tool features a temperature rise calculator so we can also calculate the temperature rise above ambient if trace current and width are given. Most of us know that resistance is also a function of temperature so, as soon as the temperature rises, the resistance and voltage drop can also be calculated.
The above features make our tool the right choice for PCB designers to calculate any of the three prominent parameters – trace widths, temperature rise above ambient, and maximum current – essential for a robust PCB design.