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Prior to routing, take plenty of time to carefully place components in proper places on your circuit boards. Careful part placement is vital to producing optimal board layouts. Place high priority parts (oscillators, high-speed interfaces such as USB, etc.) first to ensure that high priority routes are optimized. Group related parts together (for example, all power supply and battery monitoring parts should generally be grouped closely together). In general, the micro controller should be centrally located for convenient routing to all peripherals
Use 45 degree angles and minimize sharp right angles. Less of a problem today due to manufacturing processes but this is considered to be best practice
Vias and other holes in a circuit board contain a ring of metal around them known as an annular ring (for vias) or pad (for through-hole parts). These rings exist on both the top and bottom of the board; be careful not to short traces together through the copper in pads and annular rings.
To pick some from
Tips and tricks from HW members
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