Soldering switches is a straightforward process once you understand the basics: heat the joint, feed the solder, and inspect your work. Most people searching for this are building or repairing a mechanical keyboard, so that’s exactly what we’ll cover, from choosing your materials to verifying every connection works.
What You Need Before You Start
A temperature-controlled soldering iron is the single most important tool. Fixed-temperature irons from the hardware store technically work, but they make it far too easy to overheat a circuit board pad and lift it right off. Set your iron to around 330°C (626°F). You can go as high as 350°C (662°F), but don’t exceed that. Higher temperatures risk damaging the board, and lower temperatures mean you’ll hold the iron on the joint too long, which causes its own problems.
For solder, use a thin rosin-core wire in either 0.8 mm or 1.0 mm diameter. Leaded solder (typically a 60/40 or 63/37 tin-lead mix) melts at around 183°C and flows smoothly into joints, making it the easier option for beginners. Lead-free solder melts at higher temperatures, up to 218°C or above, and tends to be less forgiving. If you use leaded solder, work in a ventilated space and wash your hands afterward.
You’ll also want a brass wire tip cleaner (better than a wet sponge for tip longevity), a desoldering pump for fixing mistakes, thin solder wick for cleanup, and flush cutters if your switch pins are long enough to trim. A multimeter is helpful for testing your work at the end.
Plate-Mount vs. PCB-Mount Switches
Before you solder anything, it helps to know which type of switch you’re working with. PCB-mount switches have five pins: two metal electrical pins, two small plastic side pins for stability, and one center plastic pin for alignment. Plate-mount switches have only three pins: the two metal pins and one center guide pin. They rely on a metal plate above the circuit board to hold them steady.
If your board has five holes per switch, you can use either type. If it only has three holes, you’ll need plate-mount switches, or you can convert PCB-mount switches by clipping off the two extra plastic side pins with flush cutters. The two metal pins are the only ones that get soldered in either case.
Prep Your Iron and Workspace
When you first power on a new soldering iron, let it reach temperature and then immediately melt a small amount of solder onto the tip. This is called tinning, and it protects the tip from oxidation. A well-tinned tip looks shiny and wet with solder. An oxidized tip looks dark and repels solder, which means heat won’t transfer properly to your joints. If your tip starts looking dull during a session, wipe it on the brass cleaner and apply fresh solder.
Secure your circuit board so it won’t move while you work. A PCB holder or even a folded towel works. If you’re using a plate, mount all your switches into the plate first, then seat the assembly onto the board so the metal pins poke through the holes on the back side. Make sure every switch is fully seated and flush before you solder anything, because desoldering a crooked switch is tedious.
The Soldering Technique
This is where most beginners go wrong: they put solder on the iron tip first and then try to transfer it to the joint. Don’t do this. Melting solder onto the tip before touching the joint burns off the flux inside the solder wire. Flux is what cleans the metal surfaces and helps solder flow smoothly. Without it, you get poor joints.
Here’s the correct sequence:
- Touch the iron to the joint. Place the tip so it contacts both the metal pin and the copper pad on the circuit board simultaneously. This heats both surfaces at once.
- Wait about one to two seconds. The pad and pin need to come up to temperature before solder will flow onto them properly.
- Feed solder into the joint. Touch the solder wire to the point where the pin meets the pad, on the opposite side from the iron tip. The solder should melt and flow around the pin on its own.
- Remove the solder wire, then the iron. The whole process takes about three to four seconds per joint. Holding the iron on longer than five seconds risks damaging the pad.
A good joint forms a small cone or volcano shape with concave sides. The solder should feather out smoothly from the pin onto the pad, with no gaps between the solder and either surface. With leaded solder, a good joint looks shiny and smooth. Lead-free solder naturally looks slightly duller, which is normal.
Recognizing Bad Joints
Two common problems show up when soldering switches: cold joints and bridges.
A cold joint happens when the pad or pin didn’t get hot enough. The solder looks dull, grainy, or balled up, sitting on the surface like a blob rather than flowing into a smooth cone. The edges are abrupt instead of tapering. Cold joints create unreliable electrical connections. They might work at first and fail later. The fix is simple: reheat the joint by pressing the iron against it for two to three seconds, letting the existing solder reflow. If it still looks bad, add a tiny bit of fresh solder (and its flux) to help things along.
A solder bridge is when solder connects two adjacent pads that shouldn’t be connected. This is more common on closely spaced pins. If you spot a bridge, press your iron tip between the two pads and drag the excess solder away, or use solder wick to absorb it.
Fixing Mistakes and Removing Switches
If you need to remove a switch entirely, you’ll need to clear solder from both pin holes. A desoldering pump (also called a solder sucker) works best for this. Heat the joint until the solder melts, then press the pump’s nozzle against it and trigger the vacuum. The pump pulls molten solder out of the hole in one shot. One useful trick: if old solder isn’t melting cleanly, add a small amount of fresh solder to the joint first. The fresh flux helps everything flow, and then you can suck it all out at once.
Solder wick (a flat copper braid) is better for cleaning up residue or removing small amounts of solder from a pad’s surface. Press the wick against the joint, then press your iron on top of the wick. The copper absorbs molten solder through capillary action. Between the two tools, the pump handles bulk removal and clearing holes, while the wick handles detail work and final cleanup.
Testing Your Connections
After soldering all your switches, test every one before assembling the rest of the keyboard. The fastest method is to plug the board into a computer and use a keyboard testing website that shows which keys register when pressed. Press each switch and confirm it appears on screen.
If a switch doesn’t register, grab a multimeter. Turn the dial to the continuity setting, usually marked with a sound wave or speaker symbol. Touch one probe to each of the two solder joints on the back of that switch. When you press the switch, the multimeter should beep, indicating a closed circuit with essentially zero resistance. If there’s no beep with the switch pressed, one or both joints have a bad connection. Reheat and reflow those joints, then test again.
If a key registers as constantly pressed without you touching it, check for solder bridges near that switch or on the controller area of the board. A bridge between the wrong pads can short a circuit and produce phantom key presses.
Tips for Cleaner Work
Work in batches rather than one switch at a time. Many builders solder one pin on every switch first, check alignment, then go back and do the second pins. This gives you a chance to reheat and straighten any switch that shifted before it’s fully locked in with two solder points.
Use only enough solder to form a proper fillet. If solder is climbing up the pin or spreading beyond the pad, you’re using too much. A keyboard typically has 60 to 120 switches with two pins each, so even small time savings per joint add up. Keep your movements consistent: iron to joint, pause, feed solder, remove solder, remove iron. After every ten or fifteen joints, wipe the tip on your brass cleaner and re-tin it with a touch of fresh solder. A clean tip transfers heat faster and keeps your joints looking sharp across the entire build.