pcb - How much clearance should you include in through-hole component holes?

Is there a general rule as to how much clearance you should add to through-hole components' holes to allow them to fit easily?

For example, if I have a component with 1mm pin diameter, what should the diameter of the holes for it's pads be?

Using my calipers on a PCB I have handy, it looks like about 0.1mm is added to some holes, but I don't know if that's "normal" or not.

Answer

That (0.1mm) is too tight More like 0.25 to 0.4mm, and towards the high end if you're designing for automatic insertion of parts with bent leads. Usually 0.8mm is okay for most leads except fat diode leads, for which you can use 1.0mm.

Usually 1.3mm holes are specified for 1mm pins (for example on terminal block datasheets), sometimes 1.5mm which is really, really loose. Data sheet recommendations often err on the side of making the holes on the loose side, especially for parts like terminal blocks and relays.

If the leads are flat or square rather than round you can go a bit tighter on the diagonal dimension, assuming a round hole. For really flat leads it's better to specify a slot, of course.

Here are some recommendations (in inches, unfortunately, but 25.4 is fast to key in).

Of course if you're using some kind of special part such as a staked connector or press-fit part, follow the recommendations on the datasheet and pay attention to the tolerances too.