DIY "Pico Slim" Upgraded Raspberry Pi Pico-based Microcontrollers!

Introducing what I call... The Pico Slim! Or the Pico Stick. I'm kind of torn between the two names, but in any case, I probably can't use something with "Pico" in it as anything more than a nickname, due to trademark issues, so that's all that the name can be today. Anyhoo, this is what I call the Pico Slim, and it's a miniaturized (at least slightly), upgraded version of the Raspberry Pi Pico that so many of us know and love!

So what's special about it? Well, there are actually only a few upgrades that this board has over the Pico, but they do make it a worthwhile project to consider!

1. USB-C Port - Unlike the regular Pi Pico, I've implemented a USB-C port onto my Pico Slim boards, as that's one of my biggest gripes with the Pico.
2. Smaller Size - While my Pico Slim is a little bit longer than the original Pico (56mm vs 51mm), the Pico Slim is, as you'd expect, slimmer than the Pico! My board comes in at a width of 16.1mm as opposed to the original's 21mm. This size still allows it to fit beautifully on a breadboard, with a whole 3 free breadboard holes on the side of each of its two rows of GPIO pins when placed in the center. This also makes it more suitable for compact projects, which I think is awesome.
3. More GPIO - The Pi Pico actually doesn't fully utilize all of the I/O on the RP2040 chip that it's designed around. The RP2040 has a total of 30 GPIO pins on it, and the Pi Pico only breaks out 26 of them. My board allows access to all 30!
4. More Program Storage - The Pi Pico comes with 2MB of program storage, which is generally plenty, however for some projects, having more storage available is a must. My board is designed with the biggest flash chip that the RP2040 can support in mind, a 16MB flash chip entirely for program storage!
5. Linear Voltage Regulator - Finally, my board is designed around a linear voltage regulator instead of a switched mode power supply. This is both an advantage and a disadvantage, as this regulator is far less efficient, however, it does mean that the ADC readouts of my board should have far less noise in them than the readouts found on the original Pico.

Interested yet? If so, keep reading and I'll show you everything you need to build your own! Oh, and did I mention, it's designed with components that shouldn't require a surgeon's hands to solder? Yep! This board is designed with components that should be as hand-solder friendly as possible. Obviously the USB-C port and the RP2040 itself are more challenging, but they're still totally doable. And the smallest of the rest of the components on the board are of the 0805 size, which isn't bad to solder at all.

This project, unlike some of my others, doesn't have a supplies page that goes on for as long as some novels, which is honestly really nice. There are obviously a lot of electronic components that you'll need to buy, along with the PCBs, but outside of that, there's not too much more to worry about aside from soldering equipment. (Unless otherwise specified, the following links are not affiliate links)

Soldering Equipment

Soldering Iron - An iron with good temperature control is crucial for soldering small parts like are on this board. This is the one I use, but you can use a less expensive one as well. Make sure you have a fine-point tip!

Hot Air Reflow Station - Although this board is hand-solder friendly, the RP2040 chip is in a package that has a large ground pad on the bottom of the chip. This means that at least this chip needs to be hot air soldered, and because of that, you might as well hot air reflow the whole top side of the board. A good hot air station is important for this, this is the one I use, but a cheaper one should also suffice.

Solder - Good quality solder will make your life so much easier. Get good solder. Leaded will play nicest, but obviously uses lead which some people (myself included) don't like the idea of. This is the one I used to solder my boards.

Solder Paste - This is necessary for the hot air reflow process. Like with the solder, leaded will play nicest, with the disadvantage of the lead being present. This is the one I used to solder my boards.

Flux - Do yourself a favor, get flux! You will probably break all of your boards and cry if you don't. This is the stuff I use, and although it says its for BGA rework, I've found it to work great in pretty much everything.

Solder Wick - This is very helpful for cleaning up any solder bridges that may form when soldering the USB-C port, any wick should do as long as you add standalone flux to it when you use it.

Microscope - This is completely optional, but it sure does help a lot with aligning components and ensuring they're soldered well.

Electronic Components

Each board needs:

1x RP2040 Chip - Main CPU

1x LM1117MPX-3.3 - 3.3V Regulator

1x USB4105-GF-A-060 - USB-C Port

1x W25Q128JVSIQ - 16MB Flash Chip (Feel free to use a smaller capacity chip from the same product line if you want to save a buck)

1x ABM8-272-T3 - 12MHz Crystal Oscillator

1x PTS526SM20SMTR21 LFS - SMD Push Button

1x Red 0805 LED

2x 15pF 0805 Ceramic Capacitor

10x 100nF 0805 Ceramic Capacitor

2x 1uF 0805 Ceramic Capacitor

2x 10uF 1206 Ceramic Capacitor

2x 27 Ohm 0805 Resistor

1x 150 Ohm 0805 Resistor

1x 1K Ohm 0805 Resistor

2x 5.1K Ohm 0805 Resistor

2x 1x18 2.54mm Pitch Pin Headers

Purchase these parts from your favorite electronics components reseller (I bought mine from Mouser).

PCBs and Solder Stencil

To get the PCBs for this project, here is a link to my PCBWay shared project (PCBWay is my YouTube Sponsor) where the Gerber Files are available for both download and to order directly from PCBWay. If you order them directly with the button on the page, it won't cost you any more, and I will get a small cut of the money you spend on the boards, which helps me out a lot, as these projects can get expensive.

When ordering the boards, once the files are uploaded, all you have to do is select the color of solder mask you want, the surface finish you want, and then how many boards you'd like to buy. PCBWay should automatically detect that these are 4 layer boards, and if it prompts you to label the order of the layers, you can just close out of the window and it will be fine. Additionally, ensure that tented vias is selected, as if the vias are left exposed, some shorts under the microcontroller chip could be formed.

As for ordering an SMD stencil, at the bottom of the PCB options, you can tick the box to order a stencil with your boards. Select the settings that you want, and there are small explanations of what each setting is on the page, and you'll receive a stencil alongside your PCBs.

I'm a YouTuber, and I have made a YouTube video on this project. Please watch it before proceeding with this project, as it gives a good idea of what to expect when approaching this and there are some important details in the video that are important!

The first step to assemble one of these boards is to spread solder paste on the top of the board with a stencil. To do this, I'd recommend using some spare PCBs around the board you're putting paste onto to make sure that your stencil can sit nice and flush on the PCB, and to lock the PCB in place.

Then, place the stencil on top, align it (you'll know its aligned when you can't see any of the solder mask color through the holes) and while ensuring it won't move at all, apply some solder paste and spread it using something like an old credit card.

Carefully remove the stencil after paste has been sufficiently spread and packed into all of the holes in the stencil, and voila! There should be solder paste perfectly spread on your board, and you should be ready to stuff it with components.

Place the appropriate components on the top side of the board now. They should stick in place because of the solder paste, and once you've got everything in the right spot (which you can figure out based on the color coded diagram attached), you're ready to move on to the next step.

Now it's time to take your hot air gun and reflow the whole top side of the board. Make sure you use an appropriate temperature that won't melt the plastic on the USB-C port, but that will still melt the solder, and also ensure your air speed isn't so high that it will blow components all over the place.

Once all of the solder has melted, hold your heat on the main RP2040 chip for a while longer, and use a pair of tweezers to jiggle the chip around and even press it down slightly. This helps to ensure that you get the best possible solder connections to the chip, and that no connections will end up disconnected. There should be some balls of solder that get squished out of the sides of the chip, and these are a good sign. We'll clean them up in the next step.

Now we can use our soldering iron and a lot of flux to clean up the solder balls around the RP2040. Put flux on all four sides of the chip, and then run down each side slowly with your soldering iron to wipe away the excess solder and to melt and ensure that the joints between the chip and solder pads are formed properly. Inspect for any disconnected pads or bridged connections.

Then, on the USB-C port, check for any solder bridges and wick them away with a small piece of solder wick, a high temperature on your soldering iron, and excess flux on the area. With that done, it should be time to start work on the back of the PCB.

Now all you have to do is put the right components on the back of the PCB, and solder them in place with your soldering iron. You could use solder paste and hot air here, however it could be risky in regards to the possibility of your heat soaking through the board and desoldering things from the back of it. It is theoretically doable though, and if you're experienced in hot air soldering, by all means, go for it.

Like before, I have a color coded diagram for you to reference for the component positions, because the silkscreen component designators were too big to place on the board without a ton of overlap, making them unreadable.

Once everything is soldered, the board should be fully functional! If you're wondering about the small bodge wire that's present on my boards, it's explained in the video, but I can explain again here. I had a small design flaw on my board and had to make that connection manually for each of my boards, but this design flaw is fixed in the gerbers you'll be able to download, and you don't need to worry about it.

Now you can solder the two rows of pin headers on to the boards, if you want. If you're someone who doesn't like having these soldered to all of your boards, feel free to skip this step.

Test your boards! Plug them into a PC, and they should show up as a small flash drive. You should be able to see what is stored on them, and you should be able to upload a code to them through either Arduino IDE if you use the Pi Pico boards library, or you can drag and drop a code file onto the board through file explorer.

I also recommend testin the functionality of all 30 GPIO pins by connecting an LED to each of them and having them light the LEDs up one-by-one. This will make it obvious as to whether or not there are any bridges between pins, or pins that are flat out not soldered properly, so that you can fix them.

If your boards function properly, you're done! (Also, here's a pinout diagram) If they don't, here's a basic troubleshooting guide:

1. Check power - The red power LED should be illuminated. If it's not, there's a chance that your USB-C port's power pins aren't soldered properly, your regulator isn't soldered properly, or there's a short. You can find a short with a multimeter, or by checking the temperature of the regulator. Be careful though, when shorted, the regulator gets absurdly hot!
2. If there's a short, desoldering and resoldering the RP2040 with hot air almost always fixed it in my cases.
3. If there's no short and the LED won't light up, maybe it's soldered backwards.
4. Check USB Data - If the board doesn't recognize on the computer, make sure that the USB data line connections aren't broken or shorted together in any way.
5. If they are, check for solder bridges at the RP2040 chip and the USB-C port.
6. Otherwise, check to make sure the connections are continuous and aren't broken at any connection point.
7. Board Takes Code but Doesn't Execute It - This happened to me twice. In both cases, it was a problem with the crystal oscillator. Resolder it or replace it.
8. Some GPIO Pins Don't Work - Check for solder bridges or broken connections around the four sides of the RP2040.

Hopefully your boards work though, and I hope that you find them fun for your future prototyping and projects!