Homebrew PCBs

There is only one valid answer to that question: plated through holes or  
not?
If you have the PCBs made with plated holes the 5 mil might be enough,  
since the "barrel" inside the hole rivets the two sides together.

If you make your boards yourself, or don't have pth you need MUCH larger  
pads.
Remember, not only is it for electrical connection but more importantly as  
a mechanical mounting for the component.

What i have found to work well:
For 100mil spaced DIL ICs i use oblong pads of 1.6mm x 4mm.
This allows for a trace between pads (4x2 fits well if there is no trace  
needed in between). Run all traces in in the direction of the pads, if you  
connect to a corner pin too. If you run in from the side the trace will  
terminate exactly where the hole is. If the hole is a bit off center you  
can drill off the trace and not notice. I had such a fault keeping me  
searching for hours, so ALWAYS run the trace into one of the ends of the  
pad.

Use the same oblong pads for headers, but offset to one side on dual-row  
headers so they don't short in the middle, and make the pads wider since  
the pins of headers are drilled larger.

For resistors absolute minimum is 2mm round, preferrably more. The larger  
the component the larger the pad. Most transistors get 4x2mm or 4x1.6mm  
too. Remember to give caps larger pads as well, they are often the highest  
parts and thus most stressed.


So, you see, i make the pads as large as i can often having to use oblong  
shapes because the spacing will not tolerate large enough round pads. i  
have lifted enough pads in the early days to have learnt that lesson.

If a component is not pressed against the top of the PCB to prevent  
pushing forces on the pad it must be huge, avoid that. Use spacers and  
such if you put like LEDs in a elevated position.

ST




On Fri, 30 Dec 2005 22:50:19 +0100, alan00463 <alan00463@...> wrote:

> I am about to layout my first homemade PCB,
>
> using Eagle 4.16 Light.    My circuit will
>
> include:
>
>
> small transistors - 2N3904 and 2N3906
>
> quarter-watt resistors
>
> half watt resistors
>
> small diodes
>
> large diode
>
> small LEDs
>
> N.O. pushbutton switches
>
>
> What size pads should I make for these components?
>
> I read on the web that the ** minimum ** pad should
>
> include a 5 mil annulus (ring) around the component
>
> leads.    But I don't know what the diameter of the
>
> leads are for these components.   So let me ask you
>
> what size pads have you found to work well for these
>
> through-hole parts?
>
>
> Alan
>
>