When you get deep into the custom keyboard scene, you necessarily become intimately associated with soldering. Building a keyboard with your preferred switches requires at least a bit of soldering to get the switches attached to the PCB. That might not be the case forever, though. An increasing number of keyboards have moved to Kailh hot swap sockets, which let you change out switches in just a few seconds with no soldering required.
Soldering switches onto a PCB simply ensures the pins remain in contact with the sockets on the board. There have been various attempts over the years to make keyboards hot-swappable, but they haven't worked very well. For example, some people attach small metal tubes called "holtites" to PCB contacts that act as sleeves for switch pins. You just cram a switch in there so it mates with the board and can be removed later without desoldering. The issue with holtites and many similar solutions is that they aren't very robust, and they don't fit in all PCBs.
The Kailh hot swap sockets require boards specifically designed for them, but they solve the durability problem quite well. The sockets themselves are soldered to the bottom side of the PCB with the plugs poking through to the top where you attach the switches. The above image shows the Kailh sockets on an Input Club K-Type, the first keyboard to ship with them. To change a switch, you just need to push in the plastic tabs that hold it in the plate and pull up. You can buy hot swap sockets from retailers like NovelKeys and KBDfans for your projects, but you can't just slap them on any PCB.
Hot swap sockets make custom boards much more accessible, but they come with some drawbacks. The most prominent problem is most boards with Kailh sockets are limited to plate-mount designs. Switches with the extra PCB-mount legs on the bottom can be crowded by the socket design on the underside of the board. This problem is more pronounced on boards that also have RGB LEDs on the PCB. If you do have PCB-mount switches you want to install in Kailh sockets, you can just clip the legs off.
Without solder holding them in place, switches can come loose and wobble. Using a plate design to hold the switches (most keyboards are plate-mount) can add the necessary stability. There are some promising upcoming keyboards that might be able to address these issues, though.
Despite the compromises, hot-swappable designs are a necessary evolution in custom keyboard design. I personally like soldering to assemble my keyboards, but that's a no-go for most people. There are a few projects we'll talk about in the coming weeks that make use of Kailh hot swap sockets for exactly this reason.