layoutpcbschematics
What are the design rules that should be applied when designing a PCB layout ? I am currently using Kicad, because it is free and it is simple to use.
I made a layout for a L200 power supply. I wand to know what are the constraints for this type of PCB (power supply) and what rules I need to follow when (generally speaking) I make a layout ?
This is the layout that I made:
And this is the schematic:
You want to reduce the number of corners and straighten up some of your components.
The trace from R1 heading downwards wants moving a fraction left to remove the kink as it comes out of the resistor.
C2 can be moved up, and the two parallel traces from the negative pin can be combined into one.
D1 can move a fraction right to get rid of that little 90 degree bend as the trace from the 4561 pin 3 enters it.
I have marked them on your picture:
Some other thoughts:
You may also want to have your corners at 45 degrees, not 90 degrees (mitre). I'm not entirely certain why people do this, but I for one think it looks nicer. You could of course break with all convention and use "Any Direction" lines, but I think that looks amateurish.
You have a lot of wasted board space. Board costs money. The smaller your layout, the less board you use, the cheaper it costs.
If you're thinking of etching this yourself, you may want to think about fattening up your traces a little to ensure they transfer properly and etch well.
Oh, and most importantly:
The standard IPC-2221, "Generic Standard on Printed Board Design" is quite complete - it covers:
It is intended to
establish design principles and recommendations that shall be used in conjunction with the detailed requirements of a specific interconnecting structure sectional standard ... to produce detailed designs intended to mount and attach passive and active components.
(and you can check out the other IPC dependencies related to specific subjects such as rigid/flex circuits, high speed design etc...)
Best Answer
The rules are this:
Realize that every trace you make adds parasitic resistance and inductance.
Resistance can be calculated the wider you make traces the lower resistance they will be. Resistance is usually in the 10mΩ range or less for most traces. If the resistance of the trace is too high for the current it will heat up. If it heats too much it will burn up. A PCB trace resistance calculator will usually help you determine the temperature of the trace with the max current you think will run through it.
Inductance is also related to trace size and is usually negligible if your circuit can be affected by 100nH or less of inductance, then look into how much inductance the trace has.
You can draw in the parasitic resistance and inductance from traces in on your schematic (usually I do this on paper) to help me visualize if it will be a problem.
Another thing to consider is placement of components, with a power supply I'd also consider ways that the components could short out or heat being dissipated in components.