My flex pcbs showed up and they are just lovely. Unlike a rigid PCB, they are a kind of coppery gold translucent color with shiny copper underneath. And unlike a rigid PCB, I had to spend hours and hours carefully routing every trace in smooth, even curves, so the whole thing just has a delightful aesthetic. They came in sheets of two (right and left) with the flexes being retained in the sheet by a few small tabs. This is a great way for them to come because once they are free of their nest, they become very flexy and floppy (as planned).
Time Savings vs Handwiring:
Wiring up a dactyl with these flexes is dead simple and fast. I estimate that it takes about an hour to put on all the diodes and to solder all the switches. I’ll time myself next time when I am not taking photos (and running to microcenter), but it would be easy for someone to do in an evening, provided you are used to surface mount soldering. My first dactyl took me multiple evenings of careful snipping, bending, soldering, stripping, and checking, I would estimate that took 8++ hours.
Assembly Steps+ Notes:
Soldering to a flex pcb is a little different than soldering to a regular pcb. The big differences are that it is very floppy, and that the pcb coverlay (kind of like solder mask) has very low thermal conductivity, and it is very thin. I did all my soldering on a heat proof silicone mat, with a normal sized chisel tip on a hakko FX888D with tweezers and no magnification. You don’t need a fancy iron, but magnification can help if you are not used to components of this size. The small size components (and orientation) are important to preventing stress on the solder joints when the flexes are flexed. Below are the steps I took to solder this thing. These steps assume you already have a keyboard with the keys installed (look at the flex to make sure you install them in the right orientation- pins should be close to the bottom of the keyboard).
A note on safety: unlike rigid boards, flex boards are springy and if they release at the right time, I’m sure they could shoot some molten solder somewhere bad- say your eyes. It seems like a very good idea to wear some eye protection while working with these.
1: Remove the flex from the backing sheet. This should be done by carefully pulling the flex apart instead of tearing the flex or using a knife. find each tab and pull perpendicular to the tab take your time. Once the flex is fully free, double check to make sure there are no tabs left between the flexes.
2: Diode soldering. The cathode (marked with a line) goes on the “cup” side of the solder mask. Solder the diodes on, or if you want super detailed instructions, continue on. First, I deposited a small blob of solder on one side of every diode pad. I put the solder on the pad on my dominant hand side. Then I laid out a bunch of diodes, and lined them up so all the cathodes were facing one direction. on this board, most of the diodes are cathode-on-left so that is how I lined them up.
Once I had all my diodes ready to go, I started tacking them to the board, working towards my dominant hand. that way the iron/iron wielding hand does not have to cross over already soldered components. Once the diodes were soldered, I rotated the mat that the flex was on and tacked on the other side. if a diode didn’t look flat, I took it off and reworked it.
3: The next step is to start to install the flex. I started on the outermost row (outside the pinky row). I simply pulled the pcb up and into the shell- it was happy to extend out like a slinkie so that some of it was outside the shell while I worked. First, I made sure that the pins from the switches went through all the holes on the pcb, then I tacked down the first and last pins with solder. Once the flex was tacked, I went through and soldered each pin to its pad, making sure to get a good connection. Once the row was done I would start the next row.
4: Thumb cluster buttons are a little different- each one lives on its own little mini flex connection. It worked well for me to tack them down one at a time. NB the “L” peninsula buttons do not change orientation- the bottom side of the PCB should always face the switches.
5: Solder the micro. NB the island that the micro sits on is meant to be folded over, so that the micro sits on top of it. There is some text that says “THIS SIDE UP” to indicate the right side. If your micro came with headers on all the pins, and you don’t want to remove it, you can snip off the extra flap of material. The USB connector should point “down” towards the thumb cluster. The micro orientation might seem strange to some- its mean for a USB bulkhead like this one, so the “wrong” orientation is meant to let the cable have a nice service loop in the shell.
6: Program the micro. Plenty of tutorials on that, and I will have some files up soon to fix a few pin order mishaps that happened on these boards (one header is flipped). NB some kapton tape should be placed under the micro to prevent shorts.
What went wrong:
Inexplicably, I flipped a single header, so there may need to be separate firmwares for the left and right hands. This is annoying, but not nearly as annoying as wiring up a whole dactyl or screwing up in some way that is not a small matter of programming (SMOP).
I need to test the right side and finish my second keyboard (for the office).
How do I get one?
Twoards the end of the week I will be putting the extra prototypes up for sale. If you are interested, you can submit some info here to be notified.
Hey! where are the design files?
At the moment, I have decided not to share the design files. Unlike many projects there is little to be learned from them for repair or use. The boards are literally transparent, and the schematic is the same one thats been used on pretty much every dactyl. I have decided I want a bit of a head start selling these to recoup some of my costs before I make it easy for anyone to just go and buy a grip of them and sell them and put them up for sale (however unlikely that is).