There are a few rules and guidelines that if you follow will help you in picking the right PCB trace width. These rules work on every PCB except some special cases such as high power application and very high frequency signaling boards. Let’s get started.
When selecting the trace width for your PCB, there are three important characteristics to consider. These qualities include:
- The pitch and size of the pads that the trace will be connecting to
- The maximum space that can be allowed between traces
- The trace’s ampere capacity (the amount of current that will flow through it)
Trace Ampere Capacity
Each and every trace on a PCB has a level of current it can safely carry without failing. The trace will delaminate from the board, or burn through it if large currents pass through. This is because the currents cause the trace to heat up, and if the currents are above its capacity, the excess heat will lead to its failure. Most people think of traces as wires with zero resistance connecting two components. However, this isn’t true as they have resistance. For this reason, you should consider its current resistance when choosing the correct width. Knowing the maximum current a trace can handle and its resistance will come handy in determining the right width to use.
Trace resistance calculation is complex math and without the right tools, you may end up with wrong results. But the good news is, there are calculator online that you can use to calculate trace width.
You’ll be prompted by these online calculators to enter design specifications of the trace, such as the acceptable increase in temperature due to its dissipating power’s resistance, the maximum amperes that will flow through it, and the thickness of the copper material used.
The calculator will present you with the trace’s calculated width after entering those values. Please note that the results you’ll be presented with are only the minimums required for the width which will work for most traces on boards that use negligible current.
One of the factors that determines the cost of a PCB is its size. For this reason, it is important to keep the board’s size as small as possible when building it. However, minimizing the PCB’s size comes with some disadvantages, one of them being you’ll have limited space to route traces. But space shouldn’t be of much concern if you are building a PCB with low power signal traces. All you’ll have to do to remain with enough space for routing is to keep the traces small.
You can also determine trace width by considering the pad at it terminates to In most cases, PCB builders take the exact width measurements of the pad and use it as the trace’s width. Using the exact width of pads is always a good idea as it helps with routing traces away from other components and avoids violation of spacing between them.
So by understanding the three characteristics we’ve discussed, you’ll be able to pick the right trace widths for low signal PCBs.
Looking for more info? Check out https://www.avanticircuits.com/the-ultimate-guide-to-picking-the-right-pcb-trace-width/.