How do you decide what the pad size should be?

[jab99407]

When we design PCB, we know the size of the leads of the components but how should we decide what will be the size of the pad?

Let's assume the below three parts are being used in my PCB, what should I put the pad size for them,

5.08mm-4P PCB Mount Screw Pluggable Terminal Block Connector (4 Pin 20pair)​

1N4007

10K Resistors

 

[rjenkinsgb]

Looking at stuff I've done:

Pluggable terminals: Approx. 3.2mm pad.
4007 etc., approx. 2mm pad.
Half watt resistor around 1.6mm.

It's a balance between having enough copper for easy soldering and not making them unreasonably large.

Note that those are for PTH boards; if I were designing a single-sides board I would use somewhat larger pads where practical, as there is much less metal for solder to flow and make a good joint (and without the pad being too fragile & lifting during assembly).

 

[eTech]

For a through hole pad:

Hole size + (2 x min annular ring)
The min annular ring size is specified by the PCB manufacturer.

so...if,
Hole size = 32 mils
Min annular ring = 12 mils (JLCPCB)
then,

32mils + (2 x 12mils=24mils) = 56 mils (min PAD size)

The PAD size can be larger if you want, but it cant be smaller than min PAD size.