When dealing with high speed signals, sound signals, high current and voltage, you need to be keen about the traces of your PCB. For example, when dealing with high speed random access memory data bus signals, and you are not using a buffer, you need to make sure that the timing is just right. This can be achieved by seeing to it that the traces are not too long and that they are preferably of the same length. When the PCB traces are carrying a high AC current, you may want to be concerned with the width more than the length. In other cases, the PCB trace length and shape is an important consideration. In short, you know you have the wrong PCB trace length if your signal is compromised.
Rule of thumb
When making a PCB, aim to make your PCB as small as possible. Short but wide PCB traces are more preferred. You want signal propagation time to be as fast as possible and you want to minimize any power loss. For timing constrained applications, always use the design software to ensure that the PCB traces in question are of the same length. Most PCB software programs assume that the PCB trace is 1oz per 0.035mm of copper for all the PCB traces. If a sensor is connected to the microcontroller in a PCB, especially an analog sensor, the PCB trace should join the two using the shortest route possible.
For electromagnetic applications, it is recommended that the PCB traces should be straight and far apart from each other. Your PCB trace length should not be comparable with one tenth of the shortest frequency of your signal. For high speed signal designs, you want to make sure that the signal that leaves an output is correctly received at the input. This is achieved by controlling the impedances and matching the PCB trace lengths and width.