Electronic – How to connect external switches to this circuit board

I think that using anything to dissipate the heat when doing soldering is just some very nasty folklore, best forgotten unless fully understood.

On surface mount parts, you want to do exactly the opposite. When soldering or desoldering, you ideally want all parts to be at the same temperature: that's why people use preheat plates. When all things are at the same temperature, there's minimal thermal stress on the terminals.

On through-hole parts with just a few terminals and good access, you may find it possible to grab all the pins at once with pliers to sink some heat away. You'll find that in practice you're more likely to mechanically damage your part by doing that, than just quickly desoldering without any heat sinking. For desoldering leaded parts, the important things are:

1. Have a high-powered iron. 50W would be bare minimum. Do not use fine tips. The wider the tip, the lower the thermal resistance between the heater and the tip, and the closer the tip temperature will be to your setpoint.
2. Have an iron with temperature control based on feedback close to the tip. Otherwise your tip, in presence of a heat sink, will be cold even though you think the temperature is right.
3. Ensure that you have good thermal contact with all the pins at the same time. This means that you need to heat up a big blob of solder with your iron, and then roll it over the pins of the device. In less than a second you should be able to pull it out.
4. If your device has leads far apart, you will need multiple soldering irons, no way around. Yes, you can try and pull leads out one at a time, but it's a hit or miss if you want to preserve the part.
5. Use flux-cored solder with electronics-compatible flux. That really means a rosin-core flux. I find that water based fluxes have too low boiling point for rework, and no-clean fluxes are irrelevant since you'll have to clean stuff anyway.
6. If you can avoid it, do not play with pulling the solder out of the holes before you desolder the part. It's easy to damage the PCB and/or the part while doing so. Apply the heat, pull the part out, and only then remove the solder from the holes so that you can replace the part.

Usually, there is one pin that is making it hard to remove. That is usually the ground pin, and it will be attached to the ground plane. The ground plane will try to suck away the heat as fast as you can apply it. This is where you need a high wattage iron, so you can get it hot quickly.

On a good day, you can remove the solder, then wiggle each pin until it breaks loose. Again, usually all except the one difficult one. Then you know which one to work on.

Failing all that, there is plan "B". Destroy the connector--crush it, for example--and once all the plastic is gone, each metal contact can be dealt with on its own, instead of having a 5-piece puzzle.