The engineers of the world tend to focus on circuits, the latest components and code as important parts of an electronics project but sometimes the PCB layout is overlooked. Poor PCB layout can cause functional and reliability issues. This post provides practical tips for advanced projects that can help your PCB designs work properly and reliably.
A PCB designer, especially one working on advanced PCB projects (or 4PCB as they are commonly known) will most commonly use thickness, length and width to control the resistance of PCB trace. Resistance is a physical property of metal that is used to actually make the trace. Designers cannot change the properties of copper so focus on what you can control – the trace size.
Trace thickness is measured in ounces of copper. For example, one ounce of copper is the thickness being measured if 1oz of copper is spread evenly over 1sq foot. The thickness of this would be 1.4 thousandths of an inch. Many manufacturers can provide a thickness of 6oz.
Use a trace calculator to find the thickness and width that your traces need to be for your particular design. If you have the space on the board, you can use bigger traces to help with heat management.
These connections are made at certain points to reduce any kind of inductance and so should be accounted for in any PCB design. For instance, kelvin connections for a current sense resistor need to be placed precisely at the resistor pads and not at some random point on the traces.
On a design schematic placing them on pads or some random spot may well look the same, on the physical board the traces have resistance and inductance that could throw any measurements taken out of the window if kelvin connections are not placed correctly.
Ground is not ideal as a conductor. Care needs to be taken in the design to make sure that noisy grounds are kept away from signals that should be quiet. Ground traces need to be large enough to carry the currents that will flow. Place a ground plane under signal trace to lower impedance of those traces.
Via Size And Number
Vias have resistance and inductance, If you are designing a trace that will run from one end of a PCB to another, and you need either low resistance or inductance, then use multiple vias. This is useful for grounding filter capacitors and also high current nodes. To help work out via sizes, you can use a via size calculator.
Distance Between Mounting Holes And Traces
When designing a PCB, you should leave enough room between the copper traces and the mounting holes of the board – this will help to prevent shock hazards when the board is in use. It should be remembered that solder mask is not considered reliable as an insulator so you should take care and be sure that there is a suitable distance between the copper and any mounting hardware that may be present.