Hot plate
If you have one, this is the quickest and the most consistent. You put solder paste on every pad, place all the parts, then heat the whole board until the paste turns from grey to shiny silver.
SMD soldering kit
Ornament Assembly Guide
1 What's in the kit
Everything here is 0805 or larger, so it is all hand-placeable. Every pad on the board is printed with the value of the part that goes on it.
| Qty | Part | Where it goes | Watch out for |
|---|---|---|---|
| 1 | Yellow LED, 0805 | Very top of the tree - it's the star | Polarised |
| 4 | Green LED, 0805 | Sides of the tree - two left, two right | Polarised |
| 4 | Red LED, 0805 | Sides of the tree - two left, two right | Polarised |
| 1 | 4.7 µF capacitor, 0805 | Center of the board, above the ATtiny footprint | Unpolarised |
| 1 | 0.1 µF capacitor, 0805 | Center of the board, above the ATtiny footprint | Unpolarised |
| 5 | 310 Ω resistor, 0805 | One at the yellow LED, one beside each green LED | Unpolarised |
| 4 | 390 Ω resistor, 0805 | Beside each red LED | Unpolarised |
| 1 | ATtiny1614 | Dead center of the board, front side | Dot marks pin 1 - top-left |
| 1 | Button | Near the base of the tree | Works either way round |
| 1 | CR2032 holder | Center of the back of the board | Through-hole - always last |
| 1 | CR2032 cell | Into the holder, once the firmware is flashed | Not fitted until the very end |
Spares included
The kit ships with an extra of each LED, each capacitor and each resistor value, because 0805 parts are easy to lose. If one pings off into the carpet, you don't have to stop and order another.
What you'll need
- Iron, hot air or hot plate - any one of the three. A fine tip for hand soldering; paste plus a hot plate or air gun for reflow.
- Solder or solder paste - thin wire for hand soldering, paste if you're reflowing. Don't use both on the same joint.
- Flux - a pen or a paste. Reflow paste already contains some, but a little extra makes the joints flow.
- Fine tweezers - you cannot place an 0805 part with your fingers.
- A magnifier - a loupe, a USB microscope, or your phone's camera zoomed right in. You'll need it to check LED orientation and joints.
- Isopropyl alcohol and a small brush - to clean the flux off at the end.
- A UPDI programmer - plus a computer running Chrome, Edge or Opera. Needed at step 12.
2 Three ways to build it
All three routes end at the same board, the only real difference is when the solder goes on: with an iron you solder each part as you place it, whereas with paste you place everything first and melt it all in one pass. Use whichever you already own.
Hot air reflow
Solder paste plus a hot air gun. Reflow the whole front side at once, or work one area at a time if you'd rather keep an eye on a small section. It's also the easiest way to re-seat a single part later.
Hand soldering
A fine-tip/chisel-tip iron and a little thin solder, and you're set - that's the whole shopping list. You tack down one side the component, then solder the other side. 0805 parts are comfortably big enough to place by hand, and the whole board is about an hour's work.
What each method looks like
3 Hand soldering technique
A fine-tip/chisel-tip iron and a little thin solder is genuinely all this kit needs - 0805 parts are comfortably big enough to place and solder by hand.
Using solder paste instead?
Skip ahead to Before you start. Steps 1–9 are placement only for you, and step 10 melts everything in one pass.
Tack one pad, then solder the other
The trick with an 0805 part is never to try to solder both ends at once:
- Put a small blob of solder on one pad only.
- Pick the part up with tweezers and set it down on that tinned pad.
- Touch the iron to the pad for a moment to reflow the joint, then let go of the part.
- Now solder the other pad normally. The first joint holds the part still while you work.
What a good joint looks like
A good joint is a small, shiny fillet curving up from the pad onto the part - a concave slope, not a ball. It's smooth and it catches the light, and once you've made a couple you'll recognise one instantly. Here's the whole vocabulary:
- Shiny and concave - correct. Move on.
- Dull, grainy or blobby - a cold joint. Either the solder never fully melted or the part moved while it set. Add flux and reflow it.
- A ball sitting on top of the pad - not soldered at all: the solder never wet the part. Flux and reflow.
- Solder joining two pads - a bridge. Add flux and drag the iron away from the bridge to pull the excess solder off with it.
Every one of those is a case of adding flux and touching the joint again with the iron - nothing on that list is a disaster, and none of it needs a new part.
4 Before you start
Every pad on this board is printed with the value of the part that goes on it. That's the whole reason this guide can be a plain list: you never have to count pins or cross-reference a schematic, you just read the board. Work through it one value at a time, in the order below.
The one thing you can get wrong: LED orientation
The LEDs are polarised, and unlike a resistor or a capacitor you can't shrug and carry on if one goes on backwards - it has to come back off. Two marks make it easy to get right the first time:
- On the LED's underside there's a small printed line. It points towards the cathode end of the part.
- On the board, the silkscreen outline around each LED has a half-square notch on one end. That's the cathode end.
Point the line at the half-square and the LED is facing the right way.
Soldering Steps
Steps 1 to 9 place every surface-mount part on the front of the board. What you actually do during each of those steps depends on your method:
- Hand soldering - solder each part as you place it, so steps 1–9 finish the front side on their own, and skip step 10. The technique is in Hand soldering technique above.
- Paste methods (hot plate or hot air) - only place the parts during steps 1–9. Nothing gets soldered until step 10's single reflow pass, so don't worry that the parts are loose.
The finish line
Step 11 solders the battery holder to the back of the board, step 12 flashes an animation over UPDI, and step 13 fits the coin cell and tests. Do not fit the battery before step 12 - the chip has to be flashed first, and the cell is the last thing that goes on.
5 Assembly steps
Thirteen steps, in the order that keeps the board easiest to work on: the parts with the tightest clearance around them first, the through-hole battery holder last, and the coin cell only once the firmware is in.
-
01
The yellow LED - the star on top
Find the single yellow LED and place it at the very top of the tree. It's the star.
- The line printed on the LED's underside points at the half-square mark on the silkscreen.
Hand soldering: tack one pad, check the LED is flat and centered, then reflow the other pad. Paste: place it only - step 10 melts it.
The star of the tree - one yellow LED, one footprint, at the top. -
02
The four green LEDs - the tree's sides
Place the four green LEDs on the sides of the tree: two on the left edge, two on the right, facing each other in pairs.
Four green LEDs: two down each side, in matching pairs. -
03
The four red LEDs
Place the four red LEDs on the remaining side footprints - again two down the left edge and two down the right. Each side of the tree has four LED footprints in total, so the reds sit alongside the greens you just placed. The silkscreen tells you which footprint takes which color.
All nine LEDs placed - the star, four green, four red. -
04
The 4.7 µF capacitor
Place the 4.7 µF capacitor in the middle of the board, in the footprint directly above where the ATtiny1614 will sit.
Capacitors are unpolarised, so either orientation is correct - just make sure it's sitting flat and centered on both pads.
The 4.7 µF cap, sitting above the chip footprint in the middle of the board. -
05
The 0.1 µF capacitor
Place the 0.1 µF capacitor in the remaining mid-board footprint, sitting below the 4.7 µF you just placed. Both capacitors end up in the middle of the board, above the chip.
The two capacitors look almost identical once they're out of the bag, so the only reliable way to tell them apart is the label on the pad you took each one from.
Both capacitors in place, in the middle of the board above the chip footprint. -
06
The five 310 Ω resistors
Place the five 310 Ω resistors: one at the yellow LED on top, and one beside each of the four green LEDs.
- The resistor at the yellow LED.
- Beside each of the four green LEDs.
The 310 Ω and 390 Ω resistors look identical once they're out of the bag. Keep them in two separate piles from the moment you open the kit - the value printed on the pad is the only thing that tells them apart.
Five 310 Ω resistors: one for the star, one beside each green LED. -
07
The four 390 Ω resistors
Place the four 390 Ω resistors - one beside each of the red LEDs. That's the last of the passives.
Four 390 Ω resistors, one per red LED. Front-side passives are done. -
08
The ATtiny1614
Place the chip in the dead center of the board. This is the one part where the orientation is not optional: there's a small dot on one corner of the package, and that corner has to sit at the top-left of the footprint. The silkscreen mark (small triangle) indicates the matching corner, so line the two up before you set the chip down.
Hand soldering: tack one corner pin, re-check the alignment, then work around the rest of the pins. Paste: place it and let step 10 do the work.
The dot on the package lined up with the corner mark on the silkscreen. -
09
The button
Place the button near the base of the tree. There's no polarity to worry about - it works either way round - so just seat it flat on its pads.
That's the last of the surface-mount parts. Once this one is down, the front of the board is fully populated.
Hand soldering: hold the button flat with a finger or a pair of tweezers while you tack the first pad.
The button, seated flat near the base. Front side complete. -
10
The reflow pass
Hand soldering? Skip this stepIf you soldered each part as you placed it, the front of the board is already finished. Go straight on to step 11.
Everything on the front of the board gets soldered in this one pass. Heat the board evenly and watch the paste change appearance as it heats up and flows out.
- Hot plate - set the plate 20–30 °C above the melting point of your paste and follow the paste's datasheet. Leaded paste melts around 183 °C; lead-free (SAC305) around 217–220 °C.
- Hot air - keep the airflow at the lowest setting that works. An 0805 part weighs almost nothing and a strong stream will blow them clean off the board. Move the nozzle in slow circles and never park it in one spot.
Once the solder is molten, surface tension pulls a part that's slightly off-center back into line and up onto its pads.
Let it cool before you touch itPull the heat and let the board come back to room temperature on its own. Don't move it, don't blow on it, and don't pick it up while the joints are still liquid - a joint disturbed while it solidifies sets dull and brittle.
Freshly reflowed board, with all joints shiny and properly formed. -
11
The battery holder - the back side
Turn the board overThe holder is the only through-hole part in the kit and it goes on the back of the board.
Before the holder gets installed: put a small blob of solder on the single pad in the middle of the footprint - the one the cell's ground terminal contacts. That blob gives the cell a better connection than a bare flat pad would, and it's far easier to do now than once the holder is soldered down around it.
A small bump is all you want - just visibly raised above the surrounding copper. A big dome of solder will stop the cell sitting flat.
One small blob on the center pad - the cell's ground contact. Now drop the holder into its holes in the center of the back of the board. Orient it so the cell goes in from the top - check it against the footprint before you commit, because it only goes on one way round. Then solder the pins from the back.
Press the holder down flush before you solder the first pin, and keep holding it while that joint sets. If the pins stick through a long way, trim them with flush cutters once every joint has cooled.
The holder seated on the back with the cell opening facing up. Its pins are the only through-hole joints on the board. -
12
Flash an animation - with the cell still out
The board is built, but the chip is still blank and the board will do nothing until it's programmed. Leave the cell out of the holder for now and flash the ornament first.
- Hook up a UPDI programmer to the board's UPDI pads - either the programmer sold alongside the kit or any UPDI adapter you already own.
- Open the flasher at unixvoid.github.io/Tree_SMD_Kit in Chrome, Edge or Opera. Web Serial is required, so Firefox and Safari will not work.
- Click Connect, pick an animation from the list, and click Program Device. It writes the firmware, then reads it back to verify.
Programming also sets the brown-out fuse, which is what keeps the ornament behaving as the coin cell drains rather than glitching at the end of the cell's life. You don't have to do anything for that - it's part of the same programming step.
Stuck on "no device found"?Check the UPDI connection first, then that the board is actually getting power. Nothing has to be pressed or held for programming to work.
The programmer hooked up to the board's UPDI pads. The browser flasher does the rest. -
13
The coin cell, and the first light
Slide the CR2032 into the holder with the + marking facing up, away from the board. The flat side is the negative terminal, and that's the face that contacts the pad you pre-tinned in step 11. Check the marking on the cell against the holder before you slide it home.
Then press the button. The animation should start straight away, and pressing the button again stops it. After five minutes it stops on its own and the chip drops into a deep sleep to protect the cell - press the button to wake it up again.
A working ornament: cell in, animation running.
6 Final checks
One slow pass over both sides of the board with a magnifier catches almost everything. Work down this list before you call it finished:
- No bridges - no neighbouring pads joined by solder. Check the chip's pins first; they're the tightest thing on the board.
- No dry joints - every pad has a shiny fillet touching both the pad and the part.
- LED polarity - all nine lines pointing at their half-square marks.
- Chip orientation - the dot is still at the top-left.
- Button flat - not tilted up on one side.
- Holder flush - sitting down on the board, pins soldered from the back.
- Flux cleaned off - isopropyl alcohol and a small brush, then let it dry. Residue isn't purely cosmetic: over time it can go conductive, and it makes the next inspection harder.
Change the animation whenever you like
Whichever animation you flashed isn't permanent. Remove the battery, plug the programmer back in, open the flasher, and write a different one. Just make sure to remove the battery before hooking it up to the programmer.
7 Troubleshooting
Nearly everything that goes wrong on this board is one of three things: an LED in backwards, a dry joint, or a bridge. Here's what each symptom usually means.
| Symptom | Usually means | What to do |
|---|---|---|
| Nothing lights up at all | The cell is in the wrong way round | Take it out and refit it with the + marking facing up, away from the board. |
| Nothing lights, and the cell is correct | The programming in step 12 didn't verify, or the chip has a dry joint | Re-run the flasher, then inspect the chip's pins for joints that look dull or aren't touching the pad. |
| One LED much dimmer than its neighbours | A dry joint on one side of that LED | Reflow both pad joints at that LED. |
| The animation stops by itself after a few minutes | Nothing is wrong - it auto-stops after five minutes | Press the button to wake it up again. |
| The flasher can't find the device | The UPDI connection, or the board isn't getting power | Check the clip or probes are actually on the UPDI pads, then check the board has power. Nothing needs pressing or holding for programming. |
| Two adjacent pads joined by solder | A bridge - too much solder on one joint | Add flux and drag the iron away from the bridge; the surplus solder follows the tip. Don't try to flick it off. |
If you have to remove a part
Add flux, then heat both of the part's joints and slide it off with tweezers the moment the solder goes liquid. Don't lever it off one pad at a time - that's how pads get lifted off the board, and a lifted pad is a much bigger job than a refit.