Few PCB schematic tips — A beginners guide
- Use labels only when necessary and avoid overusing it.
2) Try to follow the conventions: Input on the left, output on the right, voltage supply on the top and, ground on the bottom.
3) Avoid four way connections
4) Don’t label on holes as when they are printed, the label doesn’t get printed.
5) Once components are placed down, it will be harder to find U1 if its label is under the soldered component.
6) Integrated circuits should have a clear indicator, like a dot or a star, next to pin 1 to make sure the IC is installed properly. Improperly installed ICs will likely be damaged or destroyed. Debugging will be easier if the pin 1 indicator is not buried underneath the IC when the IC is on the PCB.
7) Use thermal relief on component pins to make soldering easier. You may be tempted to not use thermal relief to reduce electrical and thermal resistance, but not using thermal relief can make soldering very difficult, especially when a component pad is connected to a large trace or copper fill. Large traces and copper fills act as heatsinks that can make heating the pad for soldering difficult if properly thermal relief is not used. In the picture below, there is no thermal relief on the source pin of Q1. This MOSFET may be hard to solder and desolder. The source pin of Q2 is thermally relieved. This MOSFET will be easy to solder and desolder.
8) When placing down components, make sure you have enough space to apply solder clearly onto the PCB board.
9) Show decoupling capacitors near the device they are protecting
One of the few devices where it is important to indicate physical presence of a component. Decoupling capacitors are used to smooth out the ripples at the power supply of a component, in order to effectively do this, they need to be placed physically close to the component. This proximity should be made clear in the schematic.
10) Width of your traces is also key, you want to make sure the trace can handle the current going through it. Have a thicker trace if the current is higher.
11) Ground plating Advantages:
- Electromagnetic shielding
- Lower the impedence of the path
- Assist with heat dissipation
If your design includes radio frequency range signals, you should always use a ground plane.
12) Surface mount vs. Through-hole Components
Most surface mounts are cheaper than through-hole components. It will be helpful keeping that in mind to keep the PCB printing budget to a minimum.
13) Avoid routing two (or more) high frequency signal traces in parallel with each other — According to Ampère’s law (with Maxwell’s correction) we know that a changing current induces a magnetic field around the wire, we also know that a changing magnetic field induces a current perpendicular to the direction of the magnetic field. This effect can cause two parallel wires to couple together so that a change on one wire can induce a change on the other. You can avoid this by keeping high frequency traces separate and only crossing them in perpendicular alignment.
14) Try to group similar signals together. If you have a bunch of wires coming from a single device that all perform a similar function then you should try to keep them neatly grouped until it is absolutely necessary to split them up. This will allow you to more easily follow the signal path and will help you end up with a cleaner looking board after fabrication.
15)Minimize your use of vias, but not at the cost of dramatically increasing signal paths. The simple point is that vias are a manufacturing risk. While it isn’t likely that your board house will mess up and drill a hole too large or break the conduction ring, it is completely possible. Having fewer vias on the board reduces this risk.
16) Placing components:
- Start with components that have a set physical location such as connectors or sensors that can’t be blocked
- Start with the largest ICs first and then place the smaller ICs as you go
- Try to keep all your ICs oriented in the same direction on the board
- Place the supporting devices
- Leave space for annotations and markings on the board
- Always have edge tolerance
- Group components together. For example the resistors surrounding a transistor in your schematic will also be grouped together on the PCB