A little experience about PCB line width and via copper paving

We generally have a common sense when drawing PCBs, that is, use thick lines (such as 50 mils or more) where large currents are applied, and use thin lines (such as 10 mils) for low-current signals.

For some electromechanical control systems, sometimes the instantaneous current flowing in the wire can reach more than 100A, so the thinner wire will definitely have problems. A basic empirical value is: 10A/mm2, that is, the current value that a wire with a cross-sectional area of 1mm2 can pass safely is 10A. If the line width is too thin, the line will be burnt when a large current passes. Of course, the current burned traces must also follow the energy formula: Q=I*I*t, for example, for a trace with 10A current, a 100A current burr suddenly appears and the duration is us level, then the 30mil wire is can definitely bear it. (At this time, there will be another problem: the stray inductance of the wire. This burr will generate a strong back electromotive force under the action of this inductance, which may damage other components. The thinner the longer the wire is, the stray wire the greater the stray inductance, so the actual length of the wire must be considered).

For via copper paving, the general PCB drawing software often has several options when laying copper on the via pads of the component pins: right-angle spokes, 45-degree spokes, and direct laying. What's the difference between them? Novices often don't care much, just choose one at random and just look good. Actually not, there are two main considerations: one is to consider heat dissipation can not too fast, and the other is to consider the overcurrent capability.

The direct laying method is characterized by the strong overcurrent capability of the pad, which must be used for the component pins on the high-power loop. At the same time, its thermal conductivity is also very strong. Although it is good for the heat dissipation of the component when it works, it is a problem for the circuit board soldering personnel. Because the heat dissipation of the pad is too fast and it is not easy to hang the tin, it is often necessary to use a larger wattage soldering iron and higher welding temperature reduces production efficiency. Using right-angle spokes and 45-angle spokes will reduce the contact area between the pins and the copper foil, and the heat dissipation is slow, and the soldering is much easier. 

Therefore, the choice of copper connection method for via-hole pads should be based on the application, comprehensive over-current capability and heat dissipation capability are considered together. Do not use direct-laying for low-power signal lines, and for pads that pass large currents, they must be direct laying. As for the right angle or the 45 degree angle, it depends on the beauty.