3D-Printed Circuit Boards, for Solder-free Printable Electronics

Intro-- what is this instructable? Given the schematic for a simple circuit, make it a real circuit with the base components, some conductive thread, and a 3D printer. No solder, no etching chemicals, no sending away for anything.

This Instructable is to serve as the how-to guide for a 3D-printed electronic circuit library implemented in OpenSCAD, 3D-PCB.  I recreate the full replication process of a simple analog circuit of a blinking LED made from a few transistors, capacitors, and resistors, a single LED, and a AAA battery. I will review how to import the library, and use it to place components in OpenSCAD in a grid, and teach you the basic wrapping techniques for all the included features.

Also included is a more useful example of an LED flashlight.

What do you need? The code base was developed for use by the MakerBot Replicator. Besides the basic electronic components, you will also need conductive thread. I have tried several types of conductive thread, and the best so far (by a wide margin) can be found here.

I have also found it useful to have fine point tweezers and small scissors, to aid in the wrapping and placing of components.

Links: -- www.carrythewhat.com
 -  Library for 3D-PCB
 -  Example printed electronic -- the Cutaway LED Flashlight
 -  3D-PCB Github if you would like to support the project directly
 -  Or visit our etsy shop for other info and to support indirectly

Why? We are entering an age where physical goods increasingly have a digital representation (eg www.thingiverse.com) -- and the means production of such goods are increasingly accessible (eg reprap, makerbot, etc..).  The success of Open Source Software speaks for itself. Open Source Hardware has also seen many achievements in conventional firms (eg with arduino). But future success might lie in distributed manufacturing.

While the data can be ubiquitous and free, the machines are not, and there will always be some material cost in replicating physical goods. To those without, we want to provide access to the fantastic creations these machines are capable of. To the developers of these creations, we hope to provide a valuable user base. And the economic activity generated will drive extra resources into the technologies that power it.

At CarryTheWhat? Replications, we are acting as a case study for the independent, distributed manufacturing of physical open source goods, and there are a number of other makers doing similar things.

The goal of this project in particular is to increase the scope of what can be replicated on a commodity machine. Better solutions some day might be sort of conductive putty or ink, or even a printable conductive plastic or semi-conductor material. But for now, you can print basic electronics using a plastic PCB and conductive thread. So give it a try!

Component layout:  You have a circuit diagram, like the conceptual schematic attached.  The library currently supports the following features: battery holder (AA, AAA, and coin cell), capacitor, resistor, transistor, 1xLED, 2xLED, base board, peg (and cap, for wrapping and holding things together), an SPST slide switch, and a trace hop (for intersecting threads). This example is of a simple analog transistor circuit which causes an LED to blink.

Unfortunately, there is not yet a way to automatically place the components, so you will place each component manually. Spend a few minutes analyzing the circuit, and think about how to arrange it into a grid. I have found the grid layout the easiest for placement and wrapping, but it's by no means the only possibility!

I recommend you sketch out the circuit by hand, roughly how you intend to place them (orientation and relative locations). Also, it might be a good idea to test the circuit with the components you have on a conventional breadboard.

If you prefer Blender or SketchUp, then you can import each component separately (STL files), and place them manually. If you do this, make sure you maintain the orientation so that they will print nicely.

If you are building the circuit in OpenSCAD, download the library file '3D-PCB.scad' via thingiverse or github, and put it in the same folder as your project.  You will also need to do the same for the MCAD library. At the top of your .scad file, import the library, along with the MCAD dependencies (with the paths appropriately altered if necessary):
use <MCAD/regular_shapes.scad>;
use <MCAD/shapes.scad>;
include <3D-PCB.scad>;

Each component in the library has a standardized spacing: the pegs that make up a component are a set distance from that component's center. This value can be accessed by a call to 'get_component_distance()'. If you arrange your components in rows and columns like the example, the distance between the rows and columns should be 2 times this distance. Then if components are placed next to each other on this grid, they can share a peg. Do this where possible, and you will minimize the number of threads you need to wrap.  The caps that go over the pegs will hold your components to a snug connection.

Place your components with calls to the library, along with translate and rotate about z, with as many components sharing pegs as possible.  Tip: OpenSCAD has two rendering options: a quick render and a full render. I suggest using 'quick render' (F5) to preview while placing components. But do not try to rotate or move the rendered 3D model, this only works well after a 'full render' (F6) which in this example took around 10 minutes!

When you are finished, render and export the STL circuit.

Your 3d-printed circuit board is ready to be fabricated! Make sure that the components you placed are close enough to the right orientation. Print using the standard replicator defaults, with no raft and no support.

Also, make sure you print sufficient end-caps, and a toggle-switch if applicable.

Remove and clean if necessary, and check it's integrity -- that your slide switch will slide, batteries fit well into their holders, and your peg caps are snug and don't break the pegs when inserted.

This section has detailed instructions for wrapping techniques for the various components involved. It is by no means the only way of doing it, as the process is also a work in progress.

General rules of thumb:
1. You should always try to start and end your traces at a peg
2. The tail end of a thread should come out of the side of the peg that is away from the other components (this is where the most fraying will occur)
3. When running between pegs, have the thread come out of the center (as opposed to around the side) for a more firm hold with the cap, and for straight traces at increments of 90 degrees.
4. Run your traces prior to inserting any of the components, to make them easier to change out if necessary.
5. Insert the peg caps once the components are in place. If there is an excess thread at the peg, pull it tight, insert the cap, and then snip off the excess.
6. I strongly suggest you test your circuit early and often with a multimeter; resistance of the threads should register but should not exceed a few dozen ohms.

Detailed wrapping instructions (each accompanied with pictures)
 - Peg: Start and end your trace at a peg. First, pin down a small length of thread next to the peg, and feed it through a central slot. Wrap once or twice around the perimeter, then add a few half-wraps; pass the thread through a central slot, then 3/4 of the way around the outside, then through the opposite central slot. When ending a trace, do the same procedure. Make sure to leave some extra thread to pull it taught before inserting the cap (after the components), and trim the excess to keep the fraying end in check.
- Battery: Start with a few loops around the half of the peg that is not conjoined with the sphere. Then run the thread along the perpendicular slot, into the slanted slot of the sphere itself. Wrap one or two loops around the sphere: around the contact point with the battery and then through the slot again. After these loops, run the thread back down through the central slot, and back out through the end peg. Hold everything in place by inserting a peg cap at the 45 degree angle into the peg.
- Toggle Switch: This has two components. The base of the switch is placed in your circuit, and has two pegs on either side. Wire up one end of the switch by wrapping these two pegs, but make sure your thread runs straight across as pictured. For the second part, start with the separately printed toggle. Form a loop around the front of the switch, where the connection will be made with the thread that you just ran. Follow the thread along the grooves, and tie a knot around the back of the switch, as tight as possible. Snip off any excess thread, but it's OK to leave a little there. Once this is done, snap the switch into the circuit (still with the other end of the thread untethered).  Make sure that the switch is in the ON position before you wrap the loose thread around another peg, otherwise there will not be enough slack and you'll either not be able to switch it on, or you'll force it and the thread will snap.
- Trace Hop: This is for when wires have to cross each other in the plane. You can help alleviate the need by building your circuits in two parts (with holes) and gluing them together.. but you still need sometimes to hop over a wire. Like with PCBs, these are unshielded traces. Along one direction this component has a lower slot, and in the perpendicular direction it has an upper slot.  I suggest you run the thread in the lower slot first.
- Components: the LEDs, resistors, capacitors, and transistors are all quite similar. They have two to three leads with the corresponding pegs, which should already be wrapped into the circuit board.  When you insert the components, it is helpful to have fine point tweezers to help guide the leads into the peg. If it does not slide all the way in, that's fine -- the peg cap will do the rest. Be careful when bending the leads, especially for the LED slots, because they are not particularly malleable and will break after just a few bends. Once in place, pull any excess thread at the peg and slide the cap into place.  Trim any excess thread, and use tweezers to wrap excess component lead around the peg (or clip off).

This is the detailed instructions for a case study with the library: the 3D-Printed LED Flashlight.

Tools:
- 3D Printer; right now I've only done thorough testing on MakerBot Replicator
- Needle point tweezers (helpful in wrapping and inserting components)
- Small scissors (helpful in trimming excess thread)

Bill of Materials:
(4) 5mm LEDs, you'd probably prefer white
(2) AAA batteries
(2) conductive threads ~12in each
(2) conductive threads ~18in each

Printed Bill of Materials: (all with default settings, no raft, no support)
(1) electronics top
(1) electronics bottom
(1) flashlight tube casing
(1) flashlight cap
(1) toggle switch piece
(11) end cap

First: Make sure you test your LEDs, with about the 3v from the batteries.  It also might be a good idea to test the batteries...

Detailed Instructions: Referring to the schematic attached, there are 4 traces to run. Detailed instructions for how to wrap the individual components can be found in step 3.
1.  Start on the back, the "electronics bottom" board with the two batteries. Orienting the LED slots to be up, run your first trace (~18in) between the positive end of the left battery and the negative end of the right battery (top left to bottom right). Insert end caps.
2.  Also on the back, wrap the second trace (~12in) from the positive end of the right battery, around the peg that is behind the LEDs, but in front of the batteries. Place the "electronics top" on the underside against the "electronics bottom", with the LED holders pointing in the same direction. Feed your excess thread from the peg through both holes at the peg's base, so that it emerges on the other side. Flipping the two boards over, wrap the rest of this thread around the corresponding peg next to the hole.
3. Starting on the back again, with the same LED up orientation, start the third trace (~18in) on the upper left peg.  After a few wraps, have your thread emerge from the top, to run across in front of the LEDs, and do the same wrapping on the upper right peg. Have your thread again emerge from the top, and feed it through the hole nearby.  Flipping the electronics over, wrap the two upper most LED pegs in the same fashion: solid wraps around each peg, and running across in front of the LEDs. Once all 4 are wired, you should still have decent excess thread. Run your trace down to the peg below, and across the switch.  Finish wrapping that peg, and insert a peg cap.
4. Lastly, your last trace (~12in) will be the rest of the switch attached to the battery. Start by tying the knot around the switch, as is explained in step 3.  Insert the toggle switch (should snap into place), and move it to the on position, or you won't have enough slack to operate the flashlight. Run the thread down to the peg at the base, and give it a few wraps. Then feed the thread through the hole at the bottom right, so it will emerge in the right place.  Flipping the electronics over, there is one remaining battery terminal. Wrap your excess thread around this, the negative end of the left battery. Insert peg cap.
5. Insert the components. In this case, there are 4 LEDs and two batteries to insert. In this case, I suggest inserting the batteries first, and wrap with the switch on. This way, you'll know quickly whether or not you are inserting the LEDs correctly...  For both the top and the bottom, there are two LEDs to insert.  Orient them such that the positive leads (the longer one) run down to the peg in the center, and the negative leads out to the pegs on the side.  You will need to bend the leads a little to fit properly, but be careful not to bend them too much because they are prone to breaking. Once they are all in place and working, insert the final peg caps, anywhere there was a loose thread or a component lead.
6. Put it all together. Slide the combined electronics piece into the tube, such that the switch is exposed in the cut-away. The cap then fits onto the front, and twists into place.

Congratulations, you have now printed your own flashlight!