Electronic – Through-hole footprints: pad size from technical drawings


I'm creating some footprints for through-hole components in KiCad, and I've got some issues determining the correct pad dimensions from manufacturer's technical drawings.

As an example, here's the drawing for a Fairchild BC547 – TO-92 package (line spacing lead form – dimensions in millimetres):

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First of all, having two values for the same dimension should in my understanding indicate min/max values.

I don't want the drills to be too large, as I like when the component somehow stick to the board when soldering from the bottom side.

So in such a case, what would the ideal drill size and pad size for 0.56/0.36 and spacing for 2.80/2.40?

Best Answer

You may want to have a look at the IPC through hole standards or have a look at this page, where it is a little easier to understand.

In your example:

Minimum Hole Size

Pad is 0.56mm x 0.52mm => sqrt(0.56^2 + 0.52^2) = 0.76mm Minimum Hole Size = Maximum Lead Diameter + 0.25mm = 0.76mm + 0.25mm

If you like your components to "stick" you may want to choose Level C (+ 0.15mm)

Pad Diameter

Pad Diameter = Minimum Hole Size + 0.1mm + 0.60mm = 1.01mm+0.1mm+0.6mm = 1.71mm