Component dimensions chart

[billy]

Hello :)

Is there any chart that describes the
recommended dimensions of basic components
for pcb design ?

For example I have two
resistors, 1/4 w and 1/2 w and a capacitor of 47uF/35V.
Is there a way to know their dimensions in advance in
order to decide how to place them on the pcb ?

I use the eagle layout editor where there are TONS
of different dimensions, even for a simple resistor :)
For example, I have seen pcbs using 12 mm spacing
between resistor holes, but it fits nicely to 10 mm too.
But I believe there are strict rules behind, or not ??? ?

Thanks 8)

[MP]

Billy, the design rules are really not that strict ;D. You have all the latitude you need as long as it does not fail the DRC check.
In Eagle, I normally use the resistors from the "Discrete" library. The "Resistor" libraries are for special products such as SIL, DIL and Power resistor types.
In the discrete library, I use the resus-5 package as the most common resistor. This is the standard ,5 spacing. There is also a reseu-5. This is the same resistor but with a different silk screen image.
The reason I say the design rules are not that strict are this: Suppose you have a fairly standard or simple circut. You can run a trace or two under the resistor. Now suppose you have a really tight design. By using a reseu-7.5 or reseu-10, you can run 3 or 4 traces under the resistor. You will just have more lead exposed on the top of the board. If you have quite a bit of exposed resistor leads on the top because of this, do not forget to put a piece of very small heat shrink tubing on the leads to cover them before soldering to the board. You can also use insulation from wires that you have stripped.
In the Eagle library, the capacitor packages follow the same rules. The number is the lead spacing. You can normally go through the discrete library and look at the different packages until you see the one you have. At one point, I asked the author of the program if there was a way to print out all of the library packages so that I could use it as a quick chart, but he e-mailed me back to say it could not be done without much work. Therefore, I have made a list of the packages that I keep on hand as a quick reference.

MP

[MP]

Billy, I came across this page the other day from my archives. I used to have this on my website when I was manufacturing boards. Perhaps the information will be useful to you. You will want to convert the inch references to mm. This is information on how to determine the hole size versus the pad size on a PC Board when you are laying it out. The older programs gave you the capability to change the size of the pads.

MP

PADS.pdf