Like many individuals and organisations that need to create printed circuit boards (or PCBs) for hobby or commercial projects, we wanted a way to quickly fabricate working PCBs using an in-house process that didn't involve sending every iteration of our prototypes to a professional fabrication facility.
I stress the word "working" becasue we didn't just want to see and test the size and shape of the PCB but we actually wanted to mount components, both "through the hole" (TTH) varities and "surface mount devices" (SMD), and to have it actually work, just like a professionally fabricated board.
In a nutshell, we wanted a rapid prototyping solution for creating working printed circuit boards. In our lab we still use hybrid boards which contain both TTH and SMD components to facilitate ease of handling and soldering so the solution had to cater to both types of parts.
Interestingly, our solution development started when we looked at an Instructable 3D-Printing-3D-Print-A-Solderless-Circuit-Board. However, we had to discard that solution because it wasn't suitable for our double-sided PCBs, and we also wanted the 3D printer to print the conductive tracks, vias and the other complex artifacts normally found on a professionally fabricated PCB. Above all, we wanted the process to be FAST, reliable and without the mess of corrosive chemicals.
To use this Instructable you'll need the following:
1. a dual extruder 3D printer (a single extruder printer is OK for non-working PCBs)
2. regular (non-conductive) PLA filament (or ABS) - any color
3. conductive PLA filament (preferably Graphine based; otherwise a carbon powder base) - usually black
4. your regular PCB CAD design software such as Eagle CAD or KiCAD (must produce Gerber files)
5. high conductivity "cold solder" adhesive
6. an Internet connection to access the Solargy Innovation PCB2STL file conversion service
Step 1: 3D Printer Set-Up
For reference, our workshop 3D printer is a dual extruder FlashForge Dreamer which is easy to operate and it seems to be very good value for the money. However you can use any commercially available, dual extruder 3D printer provided it can print from both extruders in a single model.
It is a good idea to completely familarise yourself with single filament printing on your 3D printer before attempting dual extruder operation. Dual extruder operation typically requires more skill and patience.
You can save yourself a lot of time and trouble by ensuring your dual extruder printer is properly calibrated before attempting to print the PCB. The print bed must be perfectly level and the height of both extruders must be exactly the same, otherwise the lowest extruder will chip bits off your PCB as it moves around or worse still, get stuck to hot filament. The Thingiverse web site (see http://www.thingiverse.com/thing:704409) has some good, free test models which will help you to check if your 3D printer set up has been optimised.
Step 2: Order Your Conductive Filament... Ahead of Time
Conductive PLA filaments are still very new on the market and are in limited supply, so get in early to get yours. While you're waiting for your new conductive filament to arrive you can use regular PLA or ABS filament in the second extruder, perferably a contrasting color so you can see the placements of tracks, vias, pads and other conducting PCB parts.
Note that all conductive filaments aren't created equal. The benchmark test for the conductivity of filament is for the filament manufacturer to create a solid, 1 cm cube of the material, attach metal plates to two opposing sides and measure the resistance between the plates. Resistivity (or conductivity) measured in this manner is called the "Volume Resistivity" or sometimes "Ohms/cm3". You may also find other measures of resistivity in the manufacturers specifications but this is the key one to look for.
A highly conductive filament should have a Volume Resistivity of less that 1 ohm per cubic centimeter. Note that, compared to a copper track on a conventional PCB, this resistance is quite high and may not be suitable for all applications, especially PCBs which are required to conduct high power. Fortunately, the Solargy Innovation PCB2STL file conversion service (that we'll come to later) has a special feature to enhance the conductivity of the PCB tracks.
In general terms, expect filaments with a Graphine base to be much more conductive and more stable than filaments which use Carbon Black as the conducting material. As the percentage of Carbon Black is increased to improve conductivity the filament becomes weaker however Graphine filament such as BlackMagic3D doesn't suffer as much from this problem. But also watch the market closely for new conductive filaments becasue a lot of research is going into this new field.
Step 3: Finalize and Save Your PCB Design
You no doubt use one of the many excellent CAD software packages to design your PCB. If you don't have a good CAD package then consider trying one of the free offerings such as Eagle CAD (both free and paid verions widely used - Eagle CAD download) or KiCAD (which is powerful but the parts library can be difficult to understand and manage. Download here: KiCad Download)
Regardless of which PCB CAD sofware you use it must have the ability to export Gerber files of your completed design. Consult your CAD software manual if you're not sure how to do this. There is normally one Gerber file for each copper layers (typically front and back), the edge cuts, the solder masks, the drill holes, silk screen/s and even where the adhesive is to be mechanically placed for SMD mounted parts.
However, for the PCB2STL file conversion we'll use here you'll only need the following (minimum) Gerber files:
- front copper
- back copper
- edge cuts
- plated through drill holes (size and locations) or PTH
- non-plated through drill holes (size and locations) or NPTH
After generating these Gerber files with your CAD software, save them to a convenient place on your computer and then zip them up using a popular file compression utility such as pkzip.
Email the zipped files to the Solargy Innovation file conversion service at firstname.lastname@example.org to receive a quote for the file conversion service. The price is generally pretty inexpensive but wil depend on the size and complexity of your PCB.
The PCB2STL service converts your Gerber files to the special 3D modelling STL files that are used by most 3D printers. Most importantly, the STL files generated by this service are guaranteed to be hole free and to have maniold faces; thus saving you a LOT of time that might otherwise be spent cleaning up the 3D drawings.
Step 4: Check Your 3D Model
The PCB2STL fle conversion service will guide you to a link where you can view your 3D model in detail before ordering.
After you've placed your order you'll be sent two .STL files containing the 3D model of your PCB; each STL file containing the model layout for an extruder.
The attached images show the internal structure of a sample PCB generated using this service including the holes, pads, vias and tracks. Note that these are fully formed 3D models which conform to professionally fabricated PCB standards; not just simple tracks placed on top of the non-conductive substrate layer.
Step 5: Load the Model Into Your 3D Printer
The way you load a model onto your 3D printer will vary and you should be already experienced in this part of the operation before you attempt printing a PCB.
Some 3D printers, like our workshop FlashForge Dreamer, have special desktop software that allow you to select, load, align and view your STL files before "slicing" your model. Slicing is the step immediately before printing and it uses software to convert the 3D model (as represented by the two STL files describing your PCB) into printer executable instructions called "G Code".
If in doubt, check your 3D printer Operator Manual for the appropriate steps relevant for yor brand of printer.
The two STL files that you'll receive from Solargy will be exactly pre-alighned with a common point of origin to facilitate loading and printing the PCB by your 3D printer software. In fact, the models must be exactly aligned becasue the conductive tracks are embedded inside the non-conducting substrate and they will only print correctly if the conductive material is fully aligned with the voids in the substrate. (The "substrate" is the equivavent of the non-conducting fibreglass board on a professionally fabricated PCB).
Step 6: 3D Print!
Hit the Print button on your 3D printer and watch it go! When it is done you'll have a 1.6mm thick, double sided PCB with all the artifacts you'd expect on a professionally fabricated PCB including tracks, pads, vias and variable sized holes.
Note that some of the smaller vias will be filled with conductive filament. This is done automatically be the PCB2STL file conversion to improve the electrical performance of the PCB. However, this shouldn't be an issue becasue vias are not normaly used for mounting components.
The PCB2STL file conversion service also automatically enhances the PCB in other ways (such as thicker tracks in places) to ensure you get maximum conductivity.
Oh! I almost forgot. The file conversion service currently supports square and rectangular PCBs. But since the board is made from plastic you can always use a pair of cutters if you need a different shape. Standard board thickness is 1.6mm (the same as standard thickness as professionally fabricated PCBs) and the largest board size is limited by the size of your 3D printer.
Step 7: Mount and Cold Solder Your Components
Obviously you can't use a hot soldering iron and conventional solder on a plastic 3D printed model, so we do the next best thing; "cold soldering".
Cold soldering is the process of using conductive adhesives to affix your components to thePCB. There are many products on the market that are designed for PCB repair, but Amazon have a great little "Circuit Writer Pen" that contains conductive silver glue that you might like to try to get started.
Work the pen carefully around as much of the pins and pads as possible to achieve maximum conduction. As with conventional hot soldered PCBs "dry joints" can be a problem without proper attention to detail. Use a high magnification lens with good lighting to check for gaps and breaks.
Feel free to leave comments below, especially if you have suggestions on how to enhance the process.