PCB Layout
PCB layout is the conversion of the connections in the schematic into a physical placement on the printed circuit board, taking into account layers, trace width, power routing and noise separation. The same schematic can turn into a board that overheats and is affected by noise with a bad layout, or into a stable product with a good one.
There are a few concrete decisions that are decisive in the layout.
- Trace width: depends on the current to be carried and the copper thickness. In 35 µm copper a path of a few amperes calls for a width in the millimetre range; on high current paths solder reinforcement or a copper area is also used.
- Layer count: two layers are enough for simple boards; in designs with a dense controller and communications, four layers noticeably improve noise behaviour because they provide a continuous ground plane.
- Separation: the switching power stage and the analog measurement stage are physically separated, and the path of return currents is kept short.
- Heat: leaving copper area under and around power components can lower the temperature without needing an additional heatsink inside the enclosure.
The layout also determines manufacturability: component spacing, accessibility of test points and connector orientations are decided at this step. Correcting these after the board has been fabricated means a new revision.
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