Before you solder: parts check and build order

The kit is here. The iron works, because you proved it on practice boards in Chapter 7. The urge to start melting solder in the next ten minutes is strong, and this chapter exists to slow you down for about an hour, because the mistakes you can make before the first joint are the most expensive ones in the whole build. Soldering a diode badly costs you two minutes of rework. Soldering fifty-eight sockets to the wrong side of a board costs you an evening with the desoldering pump and a bruised ego.

So: a parts inventory, a damage inspection, one genuinely important concept (the reversible PCB), a labeling ritual that makes the concept harmless, and the build order with its reasons. Treat it as a lab, same as always.

Lab part 1: unbox and inventory

Clear the desk, lay out a towel or a silicone mat so small parts do not bounce, and open every bag in the kit. Count everything against this checklist. Kits are packed by humans, and a missing part discovered now is an email to the vendor; a missing part discovered mid-build is a stalled project.

Print this table or copy it onto paper and tick the boxes for real:

Counts vary a little between vendors, and some pack the screws and standoffs by weight rather than by count, so a screw or two either way is normal. What you are really checking is that every row of this table is represented and that nothing electronic is short. The exact hardware counts for your kit are in its own documentation; when this table and your kit's list disagree, the kit's list wins.

Don't be confused. The PCB (printed circuit board) and the plates look similar, flat fiberglass or acrylic shapes cut in the Lily58 outline, but only the PCB has copper traces, silkscreen printing (the white lettering and symbols), and pads to solder. The plates are purely structural: the top plate holds switches straight, the bottom plate is the floor of the case. You never solder anything to a plate. If a flat part in the bag has no metal circuitry on it, it is a plate.

You are done when every row is ticked, spares are set aside in a labeled bag, and any shortage has been photographed and reported to the vendor.

Lab part 2: inspect the PCBs

Hold each main PCB up to the light and look it over on both sides:

1. Edges: no cracks, no delamination (layers of the board peeling apart), no chunks missing. Small roughness where the board was snapped from its manufacturing panel is normal.
2. Surface: no deep scratches that cut through the traces (the thin copper lines under the coloured coating). Hairline scuffs in the coating alone are cosmetic.
3. Sockets and holes: peer at the through-holes (TRRS, reset, controller rows). They should be clean rings of metal, not torn or filled with debris.
4. Bend test, gently: the board should feel stiff. Any flex with a crackling sound means shipping damage; stop and contact the vendor.

Do the same quick pass on the controllers and OLEDs. Their components are tiny and pre-soldered; you are only looking for anything visibly knocked off or crushed.

You are done when both PCBs, both controllers, and both OLEDs have passed a visual check under good light.

The one concept this chapter exists for: reversible PCBs

Here is the thing that trips up more first-time Lily58 builders than any soldering mistake, so we are going to take it slowly.

Open the kit and you will find that the two main PCBs are identical. Not mirror images. Identical, same shape, same holes, same printing. But a split keyboard needs a left half and a right half, and those are mirror images of each other. How can two identical boards become mirrored halves?

By flipping one of them over. That is the entire trick. A board that is the left half when face A points up becomes the right half when you turn it over so face B points up. Designing one board that works both ways is cheaper than designing two, so that is what the Lily58 (and most hobbyist split keyboards) does. This design is called a reversible PCB.

        The same physical board, used two ways:

        LEFT half                      RIGHT half
     (face A toward you)           (face B toward you)

      ___________                       ___________
     /  q w e r  |                     |  u i o p  \
    |  a s d f   |     same board,     |   j k l ;  |
    |  z x c v   |    flipped over     |   m , . /  |
     \___thumb___|                     |___thumb___/

     Face B is now the                Face A is now the
     BACK of this half                BACK of this half

The consequence you must burn in: every pad exists on both sides of the board. Each diode position has pads on face A and matching pads on face B. Each socket outline is printed on both faces. The board cannot know which half you have decided it is. Only you know, and you tell it by soldering components onto one specific side. Solder them to the wrong side and the board is electrically fine but physically inside out: the sockets end up where the switches should be, and everything must come off again.

So which side do the components go on? The rule, and the convention this book uses from here to the end:

Components go on the BACK. Switches go on the FRONT.

The front of each half is the side that faces you when you type: the top plate and the switches live there. The back is the side that faces the desk: the diodes, hotswap sockets, TRRS jack, reset switch, controller, and OLED headers all mount there, hidden between the PCB and the bottom plate. When you flip a finished half over, you should see all the electronics; when you look at it as you type, you should see only switches.

The labeling ritual (do this now, not later)

Decide, right now, which physical board is your left half and which is your right. There is no wrong choice, the boards are identical; the decision only becomes real when you commit solder. Then:

1. Lay a board down and orient it as the left half (thumb cluster at the bottom right of the board, keys arcing like your left hand). The side now facing up at you is its front. Flip it over.
2. Tear off a piece of masking tape, write "LEFT BACK, PARTS GO HERE" on it, and stick it to the face now showing.
3. Repeat with the other board as the right half: orient it, flip it, label the exposed face "RIGHT BACK, PARTS GO HERE".
4. From this moment, before every soldering stage in Chapter 10, you glance at the tape and confirm you are working on a labeled face. Every component in this build goes on a taped side. If you are about to solder something to a face with no tape on it, stop; something has gone wrong.

Masking tape survives soldering heat at a polite distance and peels off cleanly at the end. Two labels and thirty seconds now retire the single most common Lily58 build error.

You are done when both boards wear a tape label on their back face and you can say out loud, for each board, which half it is and which side gets parts.

The build order, and why it is not negotiable

Chapter 10 works through the components in this sequence:

1. Diodes (58 tiny ones, the flattest parts)
2. Hotswap sockets (58, low-profile)
3. TRRS jacks and reset switches (small through-hole parts)
4. OLED jumpers and 4-pin headers
5. Controller headers or sockets
6. Controllers
7. OLED screens
8. Test with tweezers before any assembly (that step lives in Chapter 12: you flash the firmware first, then short each switch position with metal tweezers and watch letters appear)

Two principles generate this order, and knowing them means you can recover if your kit's guide differs slightly.

Shortest to tallest. While you solder, the board lies component-side up, and to solder a joint well you want the part pressed flat against the board. A flat board resting on the desk does that for free. But once tall parts are mounted, the board rocks on them like a table with one long leg, and every shorter part you add afterward is a wrestling match. Diodes are about a millimetre tall; the controller on its headers is over a centimetre. Do the millimetre parts while the board still lies flat.

Hardest to undo goes last. A misplaced diode is a ten-second fix with the techniques from Chapter 8. A direct-soldered controller is 24 joints on a part you cannot afford to cook, the hardest desoldering job in the hobby. So the controller goes on last among the soldered parts, after everything under it is confirmed, and the test comes before the case closes so that any rework happens with everything still accessible.

That last point deserves its own sentence, because it is the difference between a smooth build and a frustrating one: you will test the electronics before you assemble the case. Screwing the plates on and then discovering a dead column means unscrewing everything again. Chapter 11 and Chapter 12 are deliberately interleaved for this reason, and Chapter 11 tells you exactly when to jump ahead.

Workspace, time, and your own battery

Set the bench up the way Chapter 6 described: iron and stand on your dominant side, brass-wool tip cleaner in reach, flux pen, solder, flush cutters, tweezers, and the safety glasses on your face whenever anything gets clipped. Good light matters more than any gadget here; the parts in stage 1 are the size of a grain of rice. A window open or a small fan pulling the flux smoke away from your face, as always.

Now the honest schedule. A first Lily58 build is 4 to 8 hours of bench time, and you should plan it across a weekend, not a single heroic sitting. The build is 116 diode joints, 116 socket joints, and change; none of them are hard, but they are repetitive, and soldering quality tracks your freshness almost perfectly. The first bad joint of a session is usually a sign the session should end. Natural break points: after each diode half, after each socket half, before the controllers. Stand up, drink water, come back with fresh eyes. The keyboard does not care if it gets finished Sunday instead of Saturday.

One calm paragraph about static electricity (ESD, electrostatic discharge). Chips can in principle be damaged by the little zap you sometimes feel touching a doorknob. Keyboard parts are on the forgiving end of the spectrum, and hobbyists build these boards on kitchen tables every day without incident, so no special equipment is needed. Just adopt two habits: touch something grounded (a metal lamp base, a plugged-in computer case, a radiator) before handling the controllers or OLEDs, and do not build while shuffling your socks across carpet on a dry winter day. That is the whole ESD policy.

Read the official guide too

Your kit either includes a build guide or links to one, and the original Lily58 guide lives in the kata0510 Lily58 repository on GitHub. Read it once before Chapter 10, even though it is terse and this book is not. This book explains why and teaches technique; the kit's guide is the authority on kit-specific facts: exactly which jumper pads your PCB revision uses, which way its silkscreen says the controller faces, what its plate stack order is. Where this book and your kit's guide disagree on a detail like that, the kit's guide and the silkscreen printed on your actual PCB win. Boards get revised; books cannot chase every revision.

Takeaways

• Inventory everything against the checklist before soldering anything; report shortages now, while the vendor can fix them painlessly.
• The two Lily58 PCBs are identical reversible boards; flipping one makes it the mirror half, so every board has pads on both sides and only your choice of side makes it a left or a right.
• The convention: components on the back, switches on the front. Tape labels ("LEFT BACK", "RIGHT BACK") make the convention physical. Check the tape before every stage.
• Build shortest to tallest, hardest-to-undo last: diodes, sockets, TRRS and reset, OLED jumpers and headers, controller headers, controllers, OLEDs, then an electrical test before the case goes together.
• Budget 4 to 8 hours across a weekend, take breaks before you need them, touch something grounded before handling the chips, and let the kit's own guide overrule this book on kit-specific details.

👉 Boards labeled, parts counted, bench lit. Time to make some joints. On to Soldering the boards.