Walking around the alley at Hackaday Supercon 2024, we noticed an interesting project was getting quite a bit of attention, so we got nearer for a close-up. The ‘Circuit Graver’ by [Zach Fredin] is an unconventional PCB milling machine, utilizing many 3D printed parts, the familiar bed-slinger style Cartesian bot layout and a unique cutting head. The cutting tool, which started life as a tungsten carbide lathe tool, is held on a rotary (‘R’) axis but can also move vertically via a flexure-loaded carriage driven by a 13 kg servo motor.

The stocky flexure took a lot of iteration, as the build logs will show. Despite a wild goose chase attempting to measure the cutting force, a complete machine solution was found by simply making everything stiff enough to prevent the tool from chattering across the surface of the FR4 blank. Controlling and maintaining the rake angle was a critical parameter here. [Zach] actually took an additional step, which we likely wouldn’t have thought of, to have some copper blanks pre-fabricated to the required size and finished with an ENIG coating. It’s definitely a smart move!

To allow the production of PCB-class feature sizes compatible with a traditional PCB router, the cutting tool was sharpened to a much smaller point than would be used in a lathe using a stone. This reduced the point size sufficiently to allow feature sizes down to 4 mils, or at least that’s what initial characterization implied was viable.  As you can see from the build logs, [Zach] has achieved a repeatable enough process to allow building a simple circuit using an SMT 74HC595 and some 0402 LEDs to create an SAO for this year’s Supercon badge. Neat stuff!

We see a fair few PCB mills, some 3D printed, and some not. Here’s a nice one that fits in that former category. Milling PCBs is quite a good solution for the rapid prototyping of electronics. Here’s a guide about that.

We’ve always been fascinated by things that perform complex electronic functions merely by virtue of their shapes. Waveguides come to mind, but so do active elements like filters made from nothing but PCB traces, which is the subject of this interesting video by [FesZ].

Of course, it’s not quite that simple. A PCB is more than just copper, of course, and the properties of the substrate have to be taken into account when designing these elements. To demonstrate this, [FesZ] used an online tool to design a bandpass filter for ADSB signals. He designed two filters, one using standard FR4 substrate and the other using the more exotic PTFE.

He put both filters to the test, first on the spectrum analyzer. The center frequencies were a bit off, but he took care of that by shortening the traces slightly with a knife. The thing that really stood out to us was the difference in insertion loss between the two substrates, with the PTFE being much less lossy. The PTFE filter was also much more selective, with a tighter pass band than the FR4. PTFE was also much more thermostable than FR4, which had a larger shift in center frequency and increased loss after heating than the PTFE. [FesZ] also did a more real-world test and found that both filters did a good job damping down RF signals across the spectrum, even the tricky and pervasive FM broadcast signals that bedevil ADSB experimenters.

Although we would have liked a better explanation of design details such as via stitching and trace finish selection, we always enjoy these lessons by [FesZ]. He has a knack for explaining abstract concepts through concrete examples; anyone who can make coax stubs and cavity filters understandable has our seal of approval.

Usually when we present a project on these pages, it’s pretty cut and dried — here’s what was done, these are the technologies used, this was the result. But sometimes we run across projects that raise far more questions than they answer, such as with this printed circuit board that’s actually printed rather than made using any of the traditional methods.

Right up front we’ll admit that this video from [Bad Obsession Motorsport] is long, and what’s more, it’s part of a lengthy series of videos that document the restoration of an Austin Mini GT-Four. We haven’t watched the entire video much less any of the others in the series, so jumping into this in the middle bears some risk. We gather that the instrument cluster in the car is in need of a tune-up, prompting our users to build a PCB to hold all the instruments and indicators. Normally that’s pretty standard stuff, but jumping to the 14:00 minute mark on the video, you’ll see that these blokes took the long way around.

Starting with a naked sheet of FR4 substrate, they drilled out all the holes needed for their PCB layout. Most of these holes were filled with rivets of various sizes, some to accept through-hole leads, others to act as vias to the other side of the board. Fine traces of solder were then applied to the FR4 using a modified CNC mill with the hot-end and extruder of a 3D printer added to the quill. Components were soldered to the board in more or less the typical fashion.

It looks like a brilliant piece of work, but it leaves us with a few questions. We wonder about the mechanics of this; how is the solder adhering to the FR4 well enough to be stable? Especially in a high-vibration environment like a car, it seems like the traces would peel right off the board. Indeed, at one point (27:40) they easily peel the traces back to solder in some SMD LEDs.

Also, how do you solder to solder? They seem to be using a low-temp solder and a higher temperature solder, and getting right in between the melting points. We’re used to seeing solder wet into the copper traces and flow until the joint is complete, but in our experience, without the capillary action of the copper, the surface tension of the molten solder would just form a big blob. They do mention a special “no-flux 96S solder” at 24:20; could that be the secret?

We love the idea of additive PCB manufacturing, and the process is very satisfying to watch. But we’re begging for more detail. Let us know what you think, and if you know anything more about this process, in the comments below.

Thanks to [dennis1a4] and about half a dozen other readers for the nearly simultaneous tips.

The software and hardware worlds have overlaps, and it’s worth looking over the fence to see if there’s anything you missed. You might’ve already noticed that we hackers use PCB modules and devboards in the same way that programmers might use libraries and frameworks. You’ll find way more parallels if you think about it.

Building blocks are about belonging to a community, being able to draw from it. Sometimes it’s a community of one, but you might just find that building blocks help you reach other people easily, touching upon common elements between projects that both you and some other hacker might be planning out. With every building block, you make your or someone else’s next project quicker, and maybe you make it possible.

Sometimes, however, building blocks are about being lazy.

Just Throw Pin Headers

Back when I was giving design review on a LVDS driver board for a Sony Vaio display, there was a snag – the display used, doesn’t generate its own backlight voltage, so you have to bring your own backlight driver. Well, I didn’t want to bother designing the backlight driver portion of the circuit.

The way I justified it, adding that circuit to the board didn’t make much sense – the entire board was an experimental circuit, and adding one more experiment onto it would result in extra board revisions and reassemblies. Honestly, though, I just really didn’t want to design the LED driver circuit at the time – it didn’t feel as interesting.

So, I had an easy-to-follow proposal – let’s put all backlight-driver-related signals onto three pin headers, forming a “module” footprint of sorts, and then develop the module separately! The hacker agreed, and in the meantime, used a spare panel’s LED backlight to test the display in the meantime – way more accessible of a solution. The pin headers remained, at the time, bound to be unpopulated for, at least, until the next PCB order.

New revisions of the module came and went, now bearing a HDMI port and a whole new ASIC – easy to design, because, again, the hacker didn’t have to worry about the backlight circuit, and just kept the module footprint from the previous design. Was the backlight driver module PCB designed yet? Well, simply put, no.

A friend of mine, just a month later, was designing a motherboard replacement for a tablet computer, and she asked me for advice on how to power the backlight. I thought for a second, and, I had an easy answer for her – use the module footprint. At that point, I still haven’t designed the module, but I didn’t have to mention that. She rejoiced, put the module footprint onto the board, even designed her own neat symbol for it, and then promptly went on to lay out diffpairs and reverse-engineer pinouts, both significantly more fun activities than designing a backlight driver with zero experience in design of backlight drivers.

Some time later, I started getting insistent messages from the original hacker, about needing a backlight driver. The funny part is that by that point, I have already had designed a backlight driver circuit for my own Vaio motherboard, but I never felt engaged enough to turn it into a module. A different friend of mine was looking for small projects, however. I gave her the task: here’s a footprint for a module, here’s a circuit that goes onto the module, and we need a module. Indeed, she has delivered a module – by that point, a module we could put onto three different PCBs.

Building Blocks

The entire occasion definitely helped cement my reputation as someone who delivers, eventually – with big emphasis on eventually. It also brought four people and three projects together, and it let us order the first revision PCB way sooner than otherwise, all because we set out to eventually add the backlight circuit as a module. Now, this module is a building block in our projects – whenever one of us, or maybe one of you, needs a backlight driver, we know that we have an option handy.

I have some unique experiences with PCB modules as building blocks – at one point, I’ve built an entire phone out of them, and I still build devices heavily based on modules. Whenever I’d have the occasion, I’d throw a TP4056 module footprint onto a board instead of reimplementing the whole circuit from scratch. In 2022, I designed a module with a RP2040 and the FUSB302 USB-PD PHY – it was the building block that led to my USB-C series on Hackaday, and eventually helped me, my friends, and other hackers develop a whole lineup of unique USB-C devices.

Building block use and design is the fun way, and it’s the lazy way, and it’s the friendly way – would you believe me if I told you it’s also the safe way? Say, does your circuit need a custom DC-DC, or can you slap a few pads onto the board to connect a commonplace generic module? If you can afford the increased space, might as well make your board as simple as it goes – if there’s less to test and bringup, you’ll get to your project’s finish line earlier, and have less hurdles to jump over.

The Practical Aspects

There are a few techniques you can use if you want to make a building block – pin headers are the simple obvious one. Castellations is a fun one, and here’s a trick – you don’t have to pay JLCPCB for castellated holes, as long as you are fine getting dirty ones, which are still wonderful for prototyping. If you’re using Aisler, you can get perfect castellated holes, though – good for scaling up a module of yours after you’ve verified the design. Don’t be scared of turning through-holes into castellations – it works, and it’s super easy if your board is thin enough. Oh, and you might just be able to get castellations through V-Cuts!

Got an Eastern or Western module, and it doesn’t quite use pin headers? Get out the calipers, measure its pads, and create a footprint for it – you will thank yourself later. I’ve done just once for a 5 V boost module, stocking up on them and putting them onto a bunch of boards. It’s not like I’d feel comfortable designing 5 V boost regulators at the time, so the module has bought me a couple years of worrying about something else instead. The modules have since vanished from the market, but, today I’ve got a few 5 V boost designs I can easily make modules out of. Now, it looks like I can even upgrade my own old boards that are still in use!

When designing your own boards, try to put all pin headers on a grid, 2.54 mm (0.1in) is a must – only use an integer millimeter grid or pin headers if you have no other options. Such a module isn’t just solderable – it’s breadboardable, which helps a ton when you’re trying to figure out an especially daring circuit technique. Castellated modules can be breadboardable, too, if you make sure to concentrate the core necessary signals on two opposite sides!

Are you designing a new module for your own use? See if there’s a footprint you can copy, or an unspoken standard you can follow. Boards speak about themselves through their looks, and footprints convey a purpose through their layout. Look at the boards above- it’s pretty easy to notice that they are TP4056 style battery chargers, but all of them upgraded in their own way. If you follow an existing footprint when designing your own board, it’s going to look more familiar for a newcomer hacker, channeling the power of skeuomorphism where you might not have expected to find it.

The Looks Make The Module

Board formats are underrated when it comes to accidentally creating building blocks. Sparkfun has example layouts for QWIIC devices – follow it, plop a JST-SH connector on, maybe order your PCB in red for a change, and your sensor PCB will shine in a whole new way in your eyes. Dangerous Prototypes, on the other hand, suggests a set of PCB formats known as Sick of Beige that work with existing enclosures and lasercut templates – that’s the surface-level benefit, the real deal is that these footprints also talk the Dangerous Prototypes language. If your programmer board feels like a generic rectangle, putting it into the frame of BusPirate fame will give it the air of hacker-oriented tooling. With both of these formats, you get mounting holes – mark of a hacker who knows what’s good.

Interconnect standards go hand in hand with making your building blocks’ features recognizable without reading the silkscreen – it’s why I talk so much about QWIIC, and a JST-SH connector is always a welcome addition on my boards. Adding a well-recognized standard connector makes your board recognizable as a potential building block. Now, the board looks interoperable if you just give it a chance, equipped with a familiar socket, and perhaps, you won’t feel as much need for designing a new one – quite likely, building a new device in a single day instead of two weeks’ time.

Sometimes, your board will be split apart into building blocks without your involvement whatsoever. Publishing a design that goes beyond connecting a button to an LED? Try to fill in the blanks – it’s about helping the hacker that follows in your footsteps. Sometimes it’s a highschool kid trying to put together a design, and sometimes it’ll be you again, just a couple years later. So, note down the part number of that switcher inductor in the schematic, and fill in the values of the resistor divider while you’re at it – and if you’re revisiting a board of yours where you haven’t done that, do it, then git commit and git push.

Beyond The Ordinary

There’s building blocks everywhere for those with the eyes to see. A single-board computer is one, I’d argue – a SoM in a DDR footprint is one without a doubt. An engineer once showed me a technique for creating building blocks out of thin air – taking unpopulated leftover large project PCBs, then sawing out the section with the circuit you need. Sometimes, you really only need a single piece of that one Ethernet transceiver circuit, and you need it now – you might have not planned for it, but the Dremel tool forgives all.

Circuit blocks are an often requested feature in KiCad. At the moment, you can copy-paste portions of a schematic between projects – which is more than good enough for many circuits. It’s not as great for switching regulators or MCUs, however, and we can’t help but hope to see new advancements in the field soon. Perhaps, one day, you’ll be able to click a few buttons and turn your favourite USB hub into a circuit block – and from there, who knows, maybe you can fill the void that the NanoHub’s eternal out-of-stock state has left in our hearts!

When you are troubleshooting, it is sometimes useful to disconnect a part of your circuit to see what happens. If your new PCB isn’t perfect, you might also need to add some extra wires or components — not that any of us will ever admit to doing that, of course. When ICs were in sockets, it was easy to do that. [MrSolderFix] shows his technique for lifting pins on SMD devices in the video below.

He doesn’t use anything exotic beyond a microscope. Just flux, a simple iron, and a scalpel blade. Oh, and very steady hands. The idea is to heat the joint, gently lift the pin with the blade, and wick away excess solder. If you do it right, you’ll be able to put the pin back down where it belongs later. He makes the sensible suggestion of covering the pad with a bit of tape if you want to be sure not to accidentally short it during testing. Or, you can bend the pin all the way back if you know you won’t want to restore it to its original position.

He does several IC pins, but then shows that you need a little different method for pins that are near corners so you don’t break the package. In some cases for small devices, it may work out better to simply remove them entirely, bend the pins as you want, and then reinstall the device.

A simple technique, but invaluable. You probably don’t have to have a microscope if you have eagle eyes or sufficient magnification, but the older you get, the more you need the microscope.

Needless to say, you can’t do this with BGA packages. SMD tools used to be exotic, but cheap soldering stations and fine-tipped irons have become the norm in hacker’s workshops.