[0:00] I’ve got a new PCB, but in a shocking development for the channel, this one did not come from PCBWay.
[0:06] Is this the end of the PCBWay atomic 14 relationship? Watch on to find out.
[0:11] I actually printed this PCB at home. These Voltera machines have been around for a couple
[0:17] of years now and I finally got my hands on one to do some prototyping.
[0:21] The printer uses conductive silver ink to lay down the tracks and pads.
[0:25] It’s pretty mesmerising to watch, but I’m going to speed it up a bit for this video.
[0:30] I will upload the complete print sequence as a separate video on the extras channel for you to watch.
[0:35] Once the board has been printed, we need to cure the ink by baking it.
[0:49] This is what it looks like under the microscope before it’s been baked.
[0:53] It looks kind of like someone has squeezed some marshmallows onto the PCB.
[0:56] After baking, it looks much flatter and to my eye it also looks shinier.
[1:01] We’re now ready to assemble the board, but I have jumped ahead over a whole bunch of steps,
[1:07] so let’s rewind a bit and have a look at the PCB layout and design.
[1:11] We’ve got some limitations on what we can do.
[1:13] In theory, with the Voltera you can do double sided boards. There is a drill attachment
[1:19] and you can create the equivalent of vias and plated through holes using small rivets.
[1:24] I don’t have the drill attachment and to be honest,
[1:26] I think trying to line up both sides of the board would be pretty difficult.
[1:30] So the first limitation is that I can only do single sided boards.
[1:34] To be honest, this does lead to a few routing issues, but people managed with single sided
[1:39] boards for a long time before PCB manufacturing became super cheap.
[1:43] The other limitation is that the bonding between the conductive ink and the board is not that strong.
[1:49] Here’s the previous version and I managed to snap off the header quite easily.
[1:53] So instead of trying to use a surface mount USB socket,
[1:56] which would put a lot of strain on the connection as you plug and unplug it,
[2:00] I have used a breakout board and one of these vertical surface mount sockets.
[2:03] I may try a direct USB connection in the future just to see how robust it is,
[2:08] but I’m not holding out much hope.
[2:10] The minimum trace width is 8mm or 0.2mm and we’ve also got a minimum pin pitch of 0.65mm
[2:18] for SMT/IC packages and 0603 is the smallest component size we can use.
[2:24] There’s also no silkscreen or solder resist and we have to use lead-free low temperature solder.
[2:30] Those are the only real limitations we have, but they are pretty big limitations.
[2:36] So to answer the question at the start of the video, the Atomic 14 PCBWay partnership is still
[2:42] on. We’re still going to need to use them for most of our boards, in fact they are just finishing up
[2:47] a board for me now with SMT assembly on both sides. I’m really looking forward to getting my hands on them.
[2:53] For this initial test I’ve made my traces all 0.4mm wide.
[2:58] This results in two passes of conductive ink. For a lot of the connections I could have probably
[3:03] used thinner traces and just had one pass but I decided to play it safe.
[3:07] The circuit is very simple. It’s just an ESP32-S3 module,
[3:12] a voltage regulator to take the 5v from USB down to 3.3v,
[3:16] and some LEDs so we can see the board working.
[3:19] There’s a bit of prep work to do before we can actually print.
[3:23] The first thing to do is position the circuit. The software shows us where it’s going to draw
[3:27] the PCB by moving the probe around the outline of the circuit. We can then adjust the position
[3:33] to match where we’ve clamped the board. With our circuit located, we then need to probe the height
[3:38] of the board. This needs to be really accurate so it probes a lot of points. From my board,
[3:43] this took around 3 minutes. With our height map measured,
[3:47] we can start to print. The first step is a quick calibration of the ink printing.
[3:52] I’ve attached the conductive ink and we print out a test pattern to make sure we get good results.
[3:57] With my setup, I didn’t need to tweak any of the settings so we can just wipe off the ink and print
[4:02] the PCB. This generally wipes off without any problems but you can use a bit of isopropyl
[4:08] alcohol if needed. We’ve already seen the printing stage of the process
[4:12] so I’ll speed it up to make it super fast. As I say,
[4:16] I’ll upload a normal speed version of this to the extras channel.
[4:19] Baking the conductive ink takes around 20 minutes. And once it’s cured and the machine has cooled
[4:31] down, we’re ready to dispense the solder paste. The first thing we need to do is get everything
[4:35] aligned again. The software identifies a pad on the circuit and we manually position the probe
[4:41] at the centre of that pad. We then get given another pad and we repeat the process.
[4:46] These two points are enough for the software to know where all the pads are on the board
[4:50] and we can easily sanity check this by making it go to various positions on the board and
[4:54] checking that it does actually reach the right pads. Dispensing the solder paste is really quick.
[5:00] It takes just under 3 minutes from my design and I have quite a few pads for the ESP32’s module.
[5:06] [Solder paste sounds]
[5:17] I’m always fascinated by what solder paste looks like under the microscope.
[5:21] Tiny balls of solder suspended in flux. It’s amazing technology.
[5:25] Now, my alignment was not perfect but that doesn’t really matter that much,
[5:30] we’ve got solder paste on the pads. Placing the components is all pretty straightforward,
[5:35] though I am wondering now if a pick and place machine is the next thing to add to the home
[5:39] workshop. We’ve got the various decoupling capacitors along with the RC circuit for the
[5:44] enable pin. The voltage regulator is pretty easy as it’s such a big component. And the two buttons
[5:51] are also very simple. For the LEDs, we just need to make sure we get the orientation of these
[5:56] correct. For the ones I’m using, green end is the cathode or negative. And we’ve got the matching
[6:02] current limiting resistors. I have gone for fairly arbitrary 510 ohms which will give us around 6
[6:09] milliamps for each LED. We’ve got our vertically mounted SMD header. I quite like this one as it
[6:15] has pins on both sides which should give us a nice strong connection to the board. And finally,
[6:20] the last component is the ESP32 S3 module. This is so large I can just do it by hand and gently
[6:27] nudge it into position. Reflow takes around 20 minutes. The solder does behave slightly
[6:33] differently from what you’d normally see as it doesn’t really flow on the conductive ink pads,
[6:38] but it does make a solid electrical connection between the component pins and the pads so that’s
[6:43] pretty good. Looking at the joints under the microscope, it all seems to have worked nicely.
[6:48] It is really interesting to see how different this is from normal PCBs where the solder really
[6:53] wets the pads and pins. I might tweak the footprints for the buttons in the future
[6:58] to make a more solid connection. Now of course you’ve seen this working at the start of the
[7:03] video, but when I recorded this I had no idea if this would work, so the first thing I always do
[7:08] is check that I actually get a USB device showing up when I plug the board in. And I do! Fantastic.
[7:15] So the next check is can I actually program it? I got a very basic sketch that will cycle through
[7:20] the LEDs and it uploads without any problems. Our LEDs work nicely, cycling through the blue,
[7:27] green and red. We can even get the serial output working. It’s pretty neat. Now if you observe it,
[7:33] you’ll have seen something interesting during programming. When the board is in firmware
[7:37] download mode, the red and green LEDs are both powered on. This is the real benefit of being
[7:42] able to quickly prototype things. I’ve used GPIO39 for green and GPIO40 for red. These are both used
[7:50] by the JTAG interface and this seems to have some funny behaviour in download mode. I think I’m
[7:55] going to find this new tool a really nice addition to my workshop. Well thanks for watching. If you
[8:01] want to learn more about ESP32-S3 schematics, then the playlist highlighted right now is for you.