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I'm trying to design a board that powers an MCU and a strip of Lights. The lights draw about 4A at 5V. In calculating the potential copper thickness of the PCB I'm a little lost. If i make the trace wide enough say 2cm, will that allow sufficient current flow? or do I have to create some sort of bus bar?

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    \$\begingroup\$ You need to know the copper thickness on your PCB, length of the 2cm trace, power dissipation (if its internal/external it will vary a lot for example), allowable temperature rise, allowable voltage drop. There are calculators online to give you a ballpark. You can also tin the trace for better performance (although it isn't consistent between tinnings). \$\endgroup\$ – Wesley Lee Oct 3 '17 at 18:58
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    \$\begingroup\$ That said, 2cm sounds far too wide for 4A. \$\endgroup\$ – Wesley Lee Oct 3 '17 at 18:59
  • \$\begingroup\$ There are calculators for this on-line. 4pcb.com/trace-width-calculator.html Note it also depends on plating thickness (weight) and whether the trace is internal or not.. \$\endgroup\$ – Trevor_G Oct 3 '17 at 18:59
  • \$\begingroup\$ the trace is on the outside, 2 inches long, really no specs on voltage drop ( light will work at 3 - 5 V ), temp rise ( no melting or delaminating ) 2 OZ copper \$\endgroup\$ – user379468 Oct 3 '17 at 19:02
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    \$\begingroup\$ @Trevor if you put that as an answer I will accept ... according to the calc it's 2mm not 2cm \$\endgroup\$ – user379468 Oct 3 '17 at 19:04
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There are a number of standards that provide some requirements/recommendations for determining trace width for given currents. There are several factors that come into play, such as the copper weight (thickness), expected ambient temperature, and allowed trace temperature rise. See the table below:

enter image description here

A graphical representation is also shown below:

enter image description here

IPC-2221 covers trace width requirements, and a number of websites out there have calculators based on IPC-2221. A few examples are:

Qorvo

4PCB

7pcb

SMPS

EEWEB

At their hearts the functionality is pretty much identical, so take your pick.

You might also consider a tool such as the Saturn PCB Design Toolkit which I have found to be extremely useful in designing my own projects. Off the top of my head I can't remember if it has trace width requirements based on given inputs but it might be worth checking out. In most cases, however, the above table will serve you well enough.

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