I'm working on an updated design of a PCB I made earlier this year.
The thing I want to change is to split up the single ground plane into multiple smaller ground planes, because the big ground plane acted as a huge heatsink, making it difficult to solder some parts.
Do I simply make multiple smaller ground planes, leaving small gaps between the different copper areas? Will they all still work as GND although they're not physically connected?

 

No they won't. If they are not connected, they could all be at different potentials.

 

Splitting up your ground planes is the last thing you ever want to do. Ground is your friend and you can never have too much of it. If you're having problems soldering, use a heat gun to first heat up the area where you want to solder.

 

Or use pads with thermal reliefs. Also called spoke-wheel.
Every CAD program worth its salt, offers the option that any pad soldered to a plane to be connected solid or with spokes.

 

Welcome to AAC!

the big ground plane acted as a huge heatsink, making it difficult to solder some parts.

Did you use thermals? Soldering shouldn't pose much of a problem with an adequate iron. Removal can sometimes be a problem. I've had to use a hot air tool to remove some components. Never had much problem soldering though.

I bought some low temp solder for the next time I need to remove something on a big plane.

 

Splitting up your ground planes is the last thing you ever want to do. Ground is your friend and you can never have too much of it. If you're having problems soldering, use a heat gun to first heat up the area where you want to solder.

The thing is that I'm selling this PCB as a part of a DIY-kit and some people have had difficulties soldering the ground-pins due to them taking very long to heat up. So I was wondering if there's any way to break up the ground plane to make it easier for customers to solder.

 

Welcome to AAC!
Did you use thermals? Soldering shouldn't pose much of a problem with an adequate iron. Removal can sometimes be a problem. I've had to use a hot air tool to remove some components. Never had much problem soldering though.

I bought some low temp solder for the next time I need to remove something on a big plane.

Yes, I did use thermal pads.
The thing is that I'm selling this PCB as a part of a DIY-kit and some people have had difficulties soldering the ground-pins due to them taking very long to heat up. So I was wondering if there's any way to break up the ground plane to make it easier for customers to solder.

 

Do I simply make multiple smaller ground planes, leaving small gaps between the different copper areas?

It depends. Does the design really require a ground plane? Or have you just used it for convenience?

Will they all still work as GND although they're not physically connected?

All fills to be used as ground need to be connected to ground.

 

Like everyone says - use a thermal relief. There are settings for the thermal relief, dont use the 8 point wagon wheel with thick short spokes.

Maybe configure the layout program for 2 spokes that are 100 mil long and 8 mil thick. That should desolder well, and if your customer is not great at soldering there is still one spoke left if they murder one. Finally, double check that the pins current requirement is suitable for the trace width used (google for current calculator).