Soldering Guide for Custom Keyboard Builds
Hot-swap sockets have made mechanical keyboard assembly more accessible, but many high-end and vintage-inspired PCBs still require through-hole soldering. The technique is straightforward once the fundamentals are understood — and the few minutes spent on each switch create a permanent connection that outlasts any socket.
Equipment Checklist
- Soldering iron — a temperature-controlled station rated at 60–75 W handles keyboard work comfortably. The Hakko FX-888D and KSGER T12 are popular among Singapore-based builders.
- Solder wire — 63/37 tin-lead with rosin core, 0.8 mm diameter. Lead-free (SAC305) is an alternative but requires higher temperatures and slightly different technique.
- Flux pen — Kester 951 or equivalent no-clean flux. Essential for re-work and helpful even on fresh joints.
- Desoldering pump or wick — brass wick (2.0 mm width) absorbs excess solder quickly; a spring-loaded solder sucker provides stronger suction for filled-through holes.
- Brass wire tip cleaner — gentler on plated tips than a wet sponge and does not cool the iron between joints.
- PCB holder or third hand — keeps the board stable at a comfortable angle during soldering.
Step-by-Step Process
1. Preparation
Insert the switch into the PCB from the top side, ensuring both pins pass cleanly through the corresponding holes. If a pin bends on entry, straighten it with tweezers before pushing down — forcing a bent pin risks cracking the pad.
2. Temperature Setting
For 63/37 leaded solder, set the iron to 320–350 °C. Lead-free SAC305 requires 370–390 °C. Higher is not better: excessive heat can delaminate the pad from the PCB substrate within 3–5 seconds of sustained contact.
3. Applying Solder
Touch the iron tip simultaneously to the pad and the switch pin. Wait one second for the metal to reach temperature, then feed solder wire into the junction — not onto the iron tip. A correct joint forms a small cone or concave meniscus around the pin. The entire operation should take no more than 3 seconds.
4. Inspection
A good joint looks smooth and shiny (leaded) or slightly matte (lead-free). Cold joints appear grainy or blobby and indicate insufficient heat or movement during cooling. Bridges between adjacent pads mean too much solder was applied; wick away the excess and reflow.
5. Desoldering Mistakes
Apply flux to the joint, reheat with the iron and press desoldering wick flat against the pad. The wick draws molten solder away by capillary action. For stubborn joints, add fresh solder first — the additional flux and mass help the old solder flow more readily.
Pad Repair
Overheating can lift a pad from the PCB. If the trace underneath is intact, the fix is to scrape a small section of trace bare with a craft knife, then bridge the gap with a short length of 30 AWG enamelled wire soldered to both the bare trace and the switch pin. Apply a drop of UV-cure adhesive over the repair to secure the wire mechanically.
Safety in Singapore
Lead-based solder requires ventilation. A fume extractor with an activated-carbon filter placed 10–15 cm from the work area captures rosin fumes effectively. The National Environment Agency (NEA) classifies solder waste as e-waste; used solder and desoldering wick should be disposed of at designated e-waste collection points rather than in general household bins.
A common first-timer error is soldering a switch with the plate already sandwiched in place but upside down. Always confirm the switch orientation before soldering — the two pins should be on the bottom side of the PCB, and the plate should sit flush on the top side.
Recommended Suppliers for Solder & Flux in SG
RS Components Singapore (sg.rs-online.com) stocks Kester and Multicore solder wire. For budget alternatives, Sim Lim Tower's electronics shops on the ground floor carry 63/37 rosin-core wire at SGD 4–8 per 100 g roll.