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?
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:
A graphical representation is also shown below:
IPC-2221 covers trace width requirements, and a number of websites out there have calculators based on IPC-2221. A few examples are:
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.