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If your PCBs are meant to be screwed onto something, put mounting holes on your layout, and if at all possible, use M3 screws. This is for standardization purposes. If you have a space restriction, smaller screws are finemight be fine, but check with someone mechy first.
If a pin is listed as NC (not connected) on a data sheet, don’t tie it to ground. Just leave it unconnected. Some manufacturers use NC pins for in production testing, and as such they aren’t actually high impedance pins, and shorting them elsewhere may destroy your IC.
Use plated holes for any through-hole components. This is default in most PCB design software. If a trace on the bottom and a trace on the top of the board meet at a component lead, the hole, not the lead, should be the conductor between them. Not using plated holes can cause continuity issues if the solder doesn’t wick completely through the hole during assembly.
Add debug LEDs to PCBs that use microcontrollers when possible.
If it is reasonable, route traces so that if a solder joint on one component fails (e.g. if a pad rips off), it does not affect downstream components (see Figure 1 below). This applies especially to power connections for independent parts of the circuit. Don’t daisy-chain power lines through the leads or pads of components.
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