When I created the PCBs for my Learn to Solder kit I was going for quick and dirty and cheap, and I achieved those goals, but for better PCBs it would make sense to tin them. Tinning the boards puts a thin layer of tin over the copper, which helps prevent oxidation, which can make soldering more difficult.
For a Learn to Solder kit the last thing you want is something that’s difficult to solder. (Or maybe you do want that, so it’s a challenge!) Anyway, for the PCBs I made I was able to easily scrub them with some steel wool before using, and didn’t really see much oxidation when we used them, but take a look at the photo above and you’ll see the condition of the copper just a few weeks after I made some of the boards. The one in the middle is the exception, because it has been tinned.
Just like etching, there are a number of ways to tin a PCB, and since I haven’t done it before I chose to go with the easy/expensive option. MG Chemicals has something called 421 Liquid Tin in a 125 ml Bottle. At $15 a pop it’s more expensive than other methods, but doesn’t involve heating chemical solutions, or mixing up a bunch of chemical. Don’t worry though, this stuff is still pretty dangerous, as the label on the back of the bottle will warn you.
Warnings aside, it was dead simple to use. I just put some in a plastic container with my PCB and a few minutes later it was all tinned!
This isn’t something I would have done to all of the PCBs in my Learn to Solder kit, mainly because one of the goals was to make the kits as cheaply as possible. I will be exploring the use of tinned PCBs for some future projects, some of which are more at the intersection of art and electronics, where aesthetics and how the final piece looks really matter.
I’m almost set for the Zoom Milwaukee Symposium this week. I’ll be in the Maker Plaza teaching people how to solder with the DIY kit I’ve been working on for the last few weeks. (Check out Part I, Part II, Part III, and Part IV if you haven’t seen them yet.)
It doesn’t look like a lot, but there’s over 100 PCBs that were made at home. I cut all the vinyl, etched them, drilled them, cut them apart, and sanded the edges.
There are a few options for LEDs, ranging from plain green and blue to flashing red and flickering orange. (There’s probably over 400 LEDs here.)
The resistor you use will depend on the LED you choose. I’ll be able to talk about limiting current and how it is calculated for different LEDs.
And of course there are batteries. I’ve got 100 CR2032 cells, which came in just under $18 for all of them thanks to ebay.
There are 144 binder clips to hold the batteries to the PCBs. Again the cheapest I could find, thanks to Amazon.
A few spools of solid core wire and some solder. (I’ve got more solder than this, not that we’ll need a lot, but multiple rolls are helpful.)
I also went crazy and got some Neodymium magnets in case people want to attach their PCB to other things. (I tried to arrange the magnets a bit more orderly for the photo but it was impossible!)
Here’s the back of the PCB. You can see how the board has been etched to leave just the copper traces to complete the circuit. (The ring around the edge is just a guide for the cutting and sanding.)
Here’s the front of the PCB. You can see the LED, resistor, and the wire that leads to the back through the hole which serves as the battery connector. And of course the binder clip holds the battery in place.
You can remove the arms of the binder clip if you want to stand the PCB up, attach it to something, or just be more streamlined.
And hey, with the addition of the magnet you can even turn it into a wearable! Be the envy of the Zoom After Party (wait, is there one?) with your flickering, flashing, or constantly lit LED PCB!
This is just one post in a series, check out the other posts as well:
This installment of the Learn to Solder Kit series will focus on the cutting and sanding of the PCBs we’ve been creating. This is the loud and messy part. (Check out Part I, Part II, and Part III if you haven’t seen them.)
We start with taking one of the larger board to the bandsaw and cutting apart the six boards. (The bandsaw, like many of my tools, belonged to my father. It’s quickly become one of the most used tools in the shop, right after the drill press.)
In an earlier revision of the board I left very little room to cut things apart. I just barely had the width of the saw blade, so as I etched more boards, I revised the design and increased the space to make things a bit easier.
One large board cut down to six individual boards. I also cut off any excess on the edges to make the sanding process that comes later easier.
You can see that straight lines aren’t the order of the day, which is fine. Our goal with the cutting apart is just to get things cut apart. We’ll straighten out the edges later…
Here’s a big pile of individual boards ready to have their edges cleaned up. You’ll noticed the thin edge pieces that got cut off as well, which saves us time (and dust!) when sanding.
Using the disc sander is pretty quick, but it’s also dusty, and probably my least favorite part of the process. Also, the disc sander is a cheap model someone gave me, and while I’m thankful for it, it’s loud and vibrates way more than it should.
Cleaned up edges, courtesy of the disc sander. We’ve finally got those straight lines we didn’t get on the bandsaw.
Once we have those nice clean sides on the board it’s time to round the corners. This is the part that requires a some finesse to make it nice. Sometimes I get great results, and sometimes I go quickly and say “good enough!” because I’ve got 20 more boards to do.
Oh, you might also notice a bit of “fuzz” on the edges…
Here’s the back side of the board, where you can more clearly see the fuzz left from the sanding process. This is easy to clean up.
We just lightly clean the fuzz off using the belt portion of the sander. Every now and then I drop a board while doing this and have to fish it out of the exhaust port. It’s annoying.
Here’s our nice clean board. It’s been cut apart from the larger board, and then sanded to get straight edges, given rounded corners, and cleaned up of any fuzz. Ready to go!
A big pile of finished boards at the end of the night. I can only take so much sanding in one session. Right now I’ve got 40 completed boards, and another 25 that need to be sanded. With a goal of 100 total I’ll need to etch, drill, cut, and sand about 6 more large boards (to get 36 individual PCBs) in the next two weeks in time for the Maker Plaza at the Zoom Milwaukee Symposium!
This is just one post in a series, check out the other posts as well:
If you’ve been following along as I develop a Learn to Solder Kit (see Part I and Part II) you’ll know that after etching the boards, we’ll need to add holes for all of the through-hole components that will be soldered into place.
I’ve been using a Dremel Drill Press we have in the Physical Computing Lab at UWM to drill all the holes. The bits are tiny, at 1mm or less in diameter. I’ve broken two already, so I’ve got a bunch more on order to replace the broken ones. The first one I broke right when I started drilling boards, probably because I was trying to drill a bit too fast. It’s important to remember that the bit needs to do the work of cutting. The tiny tools don’t work quite like the big tools you can be rough with. The second bit I broke was due to moving too fast, basically I’d drilled a ton of boards and was getting near the end and just didn’t take my time when moving the board, and slid it a bit before I fully lifted the bit out of it. Oh well…
Here’s a collection of drilled boards. Some are cut apart, and some are not yet cut apart. (We’ll cover the “cutting” part in a future installment.)
You’ll notice there’s one hole that is much larger than the rest. That hole is for a wire to feed through, and I drill that hole with my big drill press. The large copper pad you see is just used as a guide, and gets obliterated by the drill.
Drilling the large holes is a quick and easy operation compared to the smaller holes for the components. You’ll notice that this drilling leaves a bit of “crap” around the hole after the drill bit is lifted out of the material, so we’re going to clean that up…
Using a much larger bit (and our hands instead of the drill press) we just lightly twist the bit around a few times in a clockwise direction. This is enough to let the bit shave away the excess material. It helps to have sharp drill bits when doing this. This too is a quick operation, with just a few twists for each hole, on the front as well as the back. Clean holes are good holes!
Here’s the difference between a cleaned up hole (left side) and a bunch of non-cleaned up holes. It is an extra step to clean things up, but when you make things (and you care) it’s just something worth taking the time to do…
Now, as I’ve mentioned, I’ve been using the Dremel Drill Press at UWM for the component holes, and while it works fine, the semester is over, so I won’t be there twice a week, so I’ve been thinking about other solutions for drilling all the holes.
I could buy a Dremel Drill Press for $35 and have our friends at Amazon deliver it in two days, but there’s a few issues with that, the first of which is, my Dremel tool is old, like really old, like 25 years old maybe? Perhaps more? It belonged to my dad, and maybe even his dad. It’s old, but it works great, and I’m not planning to replace it… and sadly, I don’t think it fits the modern Dremel Drill Press, at least not without modifications.
Right now though, I probably shouldn’t be spending time trying to DIY up my own solution to a miniature drill press since I can head over to Milwaukee Makerspace and use what we have there. I know we’ve got a “ProtoDrill” thing that drills out boards. It drills from the bottom, and has a foot switch to control it. It didn’t work amazing last year when I tried it, but I’m guessing there’s a few tips to using it I wasn’t aware of. There’s also a bunch of newer Dremel tools and a mini press at the space. The fine folks at Dremel were kind enough to donate some nice tools to us after Maker Faire Milwaukee in 2014.
For my immediate needs, I can drill holes at a variety of makery places around Milwaukee, so I’m not too concerned about a solution for my home shop. I have seen a few generic “rotary tool” drill press stands, which might be easily adaptable to work with my old Dremel tool. If I don’t go the DIY route, I may just grab one of those.
Since I’m etching my own boards, there’s a number of steps in the process. I’ve covered it all in the photos below, and I’ll add in a bit of text to explain things.
I start with cutting vinyl on a Silhouette Cameo. Any vinyl cutter will do, this just happens to be the one I have at home. (We have the same model at Milwaukee Makerspace, and the DCRL has a much larger vinyl cutter.)
The vinyl after being cut. I’m using old scraps of various sizes, and I’ve got an old blade, and an old cutting mat, and sometimes it cuts almost all the way through the vinyl, but for this application it all works out fine.
Next is weeding, or removing all of the bits of vinyl we don’t need. I tend to use an X-ACTO knife to pick and grab off the pieces. It works well for tiny things like this.
The vinyl is all weeded and we’ve got a piece of transfer paper ready to apply. (The transfer paper sticks to the top of the vinyl just enough to pull it from the backing sheet.)
Once the transfer paper is down on the vinyl I press hard and rub it on good so it’ll adhere to all the tiny pieces.
Peeling back the transfer paper is best done slowly, checking to see if any vinyl doesn’t get pulled up. Occasionally you have to press it down again to grab a piece of vinyl that didn’t stick properly.
Here’s the transfer paper with all the bits of vinyl stuck to it. At this point we can stick it down onto the copper board that will be our PCB. (I usually give the copper board a light scrubbing with steel wool before sticking the vinyl on.)
Once again we press hard and rub the transfer paper onto the copper board, and then peel back slowly making sure we don’t lose any tiny bits of vinyl in the process…
And here’s our copper board with the vinyl resist in place. The vinyl works as a mask to protect the copper from being etched away. Anywhere you don’t see vinyl you won’t see copper when we are done.
Over to the PCB etching machine! It’s what we might call “janky” because I constructed it very quickly to etch some PCBs and it worked well enough that I never built a better one. I did upgrade from a servo to a DC gear motor at some point, but the bearings are still riding on smooth rods much smaller than they should be. Again, it works, so I don’t mess with it.
After adding equal parts hydrogen peroxide and vinegar to the tank (which is a food container from Noodles & Company) I put the copper board into the solution…
The board tends to float at first so I push it down with a brush. (I also use the other end of the brush to wipe away the solution while the board is etching.)
Yes, my chemical mix is hydrogen peroxide and vinegar, with a dash of salt. There are other things you can use, but this combo isn’t really dangerous, and can be easily disposed of by pouring down the drain with plenty of water. If I can avoid harsh acids, I will. It does take a bit longer to etch, but that’s where the salt comes in.
Once I start the agitation process to keep the board and liquid moving back and forth, I throw a bit of salt into the mix, which activates things and tends to foam up a bit. The foam means it’s working!
This is about 45 minutes into the etching process. You can see that the copper is nearly gone all around the edges, but not as much in the middle.
Here’s the 50 minute mark after adding a pinch more salt to the mix. It’s mostly etched but still has more copper to eat.
At about an hour and ten minutes the board is fully etched. Time tends to vary depending on if I reuse the solution or start fresh. I’m typically not in a hurry and tend to reuse solution a lot, which does take longer, but means I’m wasting less solution.
Once the board is done I pull it out and use a razor blade to gently remove the pieces of vinyl. They tend to come off fairly easy, but they are wet and stick to everything, including fingers, razor blades, the board, and anything else within 50mm of the work area.
After the vinyl is removed I wash and rise the board and then dry it and give it another quick scrub with steel wool.
We’ve now got a PCB, or a “Printed Circuit Board” as they are commonly known. (Somehow almost everything I do revolves around “printing” somehow…)
That covers the etching, so the next steps are to drill all the holes and to cut the boards apart.
Oh, you’ll also want to check out this mesmerizing video featuring the PCB Etching Machine in action. Agitation is the name of the game!
This is just one post in a series, check out the other posts as well:
