What's the best way to install my foam in a soldered build?
People might notice that some plate foams offered are 4mm and some are 3mm. Why is this? Cherry spec for switches is 5mm between the switch and the PCB. Standard plates are 1.5mm, FR4 plates are frequently 1.6-1.7, so this leaves a gap of ~3.5mm, and the choice of using 3mm foam with a gap or 4mm foam with compression.
For builds that tend to be firmer like tray mounts and that have aluminum or brass plates as the "stock" build, I typically choose to use 4mm, as that is, in my opinion, the best choice for most folks. Using thicker foam with compression usually does a better job of suppressing plate ping and, for tray mount builds in particular, normalizes the feel across the plate leading to a more consistent typing experience.
For flexier builds like gasket mounts, I typically use 3mm, to respect the flexy feel that the build is trying to achieve.
Specifically for 4mm plate foams, though, using best practice for how to solder switches in is very helpful as far as establishing consistent compression and having the switches sit properly.
How do I usually do this?
Install all your switches into the plate, place the foam over the plate/switch combo, and then push it into the PCB. Then, compress it together.
Solder 1 pin of each switch in the board.
Then, holding the PCB/foam/plate sandwich between your fingers, reflow each switch under pressure, maintaining the pressure until the solder has resolidified. This establishes a mechanical connection at each switch point keeping the foam under compression with the switches firmly seated in the PCB. Once you have done this for the whole board, then continue on and solder the 2nd pin.
Hope this helps some people out there. Any questions, please feel free to hop into the discord and ask.