[sdiy] Size guidelines for PCB pads, holes, traces?

[Vesa Lahteenmaki]

>Can someone offer some measurements appropriate for laying out PC boards 
>for
>synthesizer modules? I am new to PCB design and I am unsure how to choose
>appropriate sizes for the traces, pads, and holes.
>
>--Adam
>

some rough guidelines for old fashioned non-smd pcbs:

through plated hole size = component leg diameter + 0.3 mm ( 12 mils )

Pad size = hole size + 0.8 mm, but even bigger if holes are not plated.

axial part ( resistor, diode, etc ) pitch  = component body lenght + 7 x 
component leg diameter.  You might damage the part if you bend those legs 
too close to the body.

The track width isn't very important in analog circuits.  You are not 
pulling much current from the power supplies in these synth modules, so need 
not very fat tracks even there. Here one calculator:
http://www.geocities.com/CapeCanaveral/Lab/9643/TraceWidth.htm

Should you  make your own pcbs, like using Press-n-Peel stuff, you would use 
relatively fat tracks, lets say  mimimum 0.5 - 1mm ( 20-40 mils).  If you 
are good, you might have success with 0.3 mm tracks, but why ask for 
trouble.

Minimum gap is usually same as the track width.

More important than the width is the lenght of track. Do to your best to  
try to minimize the tracks going to the inputs of an opamp for example.  
These are high impedance and you really don't want to pick up any garbage.


Track width is quite different issue in todays high speed digital logic, 
where tracks are impedance matched, the bus signals are matched in lenght 
etc.  The thinnest tracks that I have ever used were just 70 um wide ( 100 
ohm differential pair ) and this 16-layer board had over 19000 vias, most of 
which were blind laser drilled microvias, had very big 1mm pitch bgas etc.

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