Adding Backlighting to Your Build

You've decided on the style of lighting you want for your keyboard. Now, let's get down to the practical steps of making it happen. Adding backlighting requires ensuring that all your components are compatible and, in some cases, a bit of soldering.

This guide will walk you through the process of checking compatibility, gathering the right components, and successfully installing lighting in your custom keyboard.

Step 1: Check Your PCB for LED Support

This is the most critical step. Not all PCBs support backlighting. You need to check the product description or documentation for your specific PCB to confirm its capabilities.

For Per-Key Backlighting:
- SMD RGBs: Look for terms like "per-key RGB" or "pre-soldered SMD LEDs". If the PCB already has small, square LEDs on it, you're all set! This is the easiest option as no soldering is required from you.
- Through-Hole LEDs: Look for "supports through-hole LEDs" or "2-pin LED support". You will see two small holes next to each switch position on the PCB. This means you will need to buy and solder the LEDs yourself.
For Underglow:
- Look for "RGB underglow" or "underglow support". You will typically see a strip of pre-soldered SMD LEDs on the bottom of the PCB.

If your PCB does not explicitly mention any LED support, it likely cannot have backlighting added to it.

Step 2: Ensure Your Switches are Compatible

If you're adding per-key backlighting, your switches need to let the light through.

SMD LEDs: You need switches with a large cutout at the bottom of the housing to allow the surface-mounted LED to shine through. Most modern switches designed for enthusiasts (often called "SMD compatible") have this.
Through-Hole LEDs: You need switches with a "slot" or holes in the top and bottom of the housing that allow the two legs of the LED to pass through the switch itself.

Step 3: Installing Through-Hole LEDs (If Necessary)

If your PCB uses through-hole LEDs, you'll need to install them yourself. This is usually done after you have soldered your switches to the PCB.

Get the Right LEDs: You'll typically need 1.8mm or 2x3x4mm LEDs, as larger 3mm or 5mm LEDs may interfere with keycaps.
Check Polarity: LEDs have polarity, meaning they only work in one direction. There's a long leg (anode, positive) and a short leg (cathode, negative). The PCB will have markings to show you which way to insert them. A square pad usually marks the anode.
Insert the LED: Push the LED legs through the switch and then through the corresponding holes in the PCB.
Solder: Solder the legs to the pads on the PCB.
Trim: Use a pair of flush cutters to trim the excess length from the LED legs.

Tips for Clean, Consistent Results

Polarity marking: Use a sharpie dot on the short leg as you unpack LEDs so you don’t mix orientation.
Batch workflow: Seat and bend 10–15 LEDs at a time, then solder that group. This keeps the board manageable.
Thermal control: A small chisel tip at ~320–350°C with leaded solder makes quick, shiny joints that reduce heat stress on LEDs.
Avoid mechanical stress: Don’t twist LED bodies after soldering; trim legs flush to prevent shorts against cases or plates.

Step 4: Firmware Enablement and Tuning

Once the hardware is in, ensure your firmware knows how to drive it.

QMK keycodes: Map controls like RGB_TOG, RGB_MOD, RGB_VAI/VAD, RGB_HUI/HUD, and RGB_SAI/SAD to a function layer.
Brightness cap: Set a safe global limit in your keymap or via VIA/VIAL to avoid brownouts and flicker.
Modes and speed: Start with static colors to verify all LEDs, then explore animations. Slow down waves to reduce perceived flicker on low-refresh cameras.

Step 5: Underglow Considerations

If your PCB features an underglow strip:

Diffusion matters: A frosted acrylic bottom or polycarbonate mid-layer spreads light and hides LED hotspots.
Clearance: Ensure standoffs and screws don’t block LEDs; choose shorter hardware or countersunk screws if needed.
Desk surface: Light wood or white mats enhance glow; black mats absorb it.

Step 6: SMD Rework (Advanced)

If replacing a failed SMD RGB LED:

Mask nearby components with Kapton tape.
Apply flux, then heat with hot air until the LED floats; lift gently.
Clean pads with wick, re-tin lightly, align a new LED observing orientation notch.
Reflow and nudge into place; verify color channels before reassembling.

Final QA Checklist

All LEDs light in a static white test without flicker.
No single-color failures (check red/green/blue individually).
Brightness at everyday setting (<40%) looks even across the board.
Case assembled without pinching wires or contacting trimmed LED legs.
Firmware layer with lighting controls is reachable and documented in your README or build notes.

Step 4: Choose a Compatible Case

As we mentioned in the previous section, if you want underglow, you must have a case with a transparent or translucent element to let the light out. A solid aluminum case will block all underglow.

With your hardware all sorted, the final step is to take control of your lights. Next, we'll explore how to do that with the most popular keyboard firmware: Controlling Your Lights with QMK.

Common Mistakes to Avoid

Expecting per-key RGB through opaque keycaps—use doubleshot shine-through or pudding caps for maximum effect.
Forgetting LED height: Tall through-hole LEDs can interfere with some keycaps; stick to 1.8mm or 2x3x4mm profiles.
Maxing brightness on old USB hubs: Sudden disconnects can be power-related; try a direct motherboard port or lower brightness.