# ConductiveMaterials

ConductiveMaterials

Release status: experimental

 Description experiments into conductive materials that can be extruded License GPL 2.0 Author Chip936 Contributors Based-on Delta Categories Materials CAD Models none External Link none

# Overview

This page lists the results of conductive materials that can be extruded by a Reprap printer. The goal being to be able to print uOhm conductive paths, N and P type semiconductor material and variable resistive paths.

Solders, paints, sealants, glues and epoxies.

## Low resistive materials

• Field's metal - Melting Point: 60.5 C
• Wood's metal - Melting Point: 71 C
• Rose's metal - Melting Point: 109 C
• Solder - Melting Point: 183 C
• Carbon Powder - Melting not possible - Mix in with glue or sealant - Allows for variable resistor values
• Carbon Black - nanopowders are available in a range of conductivities and sizes that may be mixed with a vehilce for inkjet or screen printing
• Graphite - nanopowders are also available in a range of conductivities and sizes that may be mixed with a vehilce for inkjet or screen printing
• Silver - nanoparticles that also maybe be mixed with nonpolar solvents or water to produce an ink for inkjet or screen printing
• Copper - nanoparticles that are coated with a resin to keep them from oxidizing until they are sintered after printing. Copper plating is also used with printed metal nanopowders. Conductive traces are first printed that are then plated to produce a finished low resistance circuit board.

## N type semiconductor material

• Zinc Oxide
• Cadmium arsenide - Soluble in water
• Tin Dioxide
• Organic semiconductors

## P type semiconductor material

• Copper Sulfide
• Copper(II) Oxide
• Organic semiconductors

## Insulators and Dielectrics

• Polymers such as polyesters, polypropylene, acrylics, urethanes

## Printing Electronics

Passive and active elctronics may be printed via inkjet, screen or flexo. A comination of conductors, semiconductors, dielectrics and insulating fluids are used in various layers to produce components or complete circuits.

The limiting factors of printing electronics are the drop sizes of the inkjets that make up the geometry of the junctions and the carrier mobility of the organic semiconductor fluids.

There are hundreds of papers available online that discuss the details of sucessfully printed electronic circuits by various printing methods.

## Print a Transistor

The holy grail of electronics is the transistor. If a 3D printer was able to extrude a mixture with Zinc Oxide, then place a dab of a mixture with Copper(II) Oxide and then attach two low resistive connections to the Zinc Oxide mixture and one low resistive connection to the Copper Oxide mixture, we should have an NPN transistor. Once we have transistors we can build [Logic Gates]. Once we have logic gates, we can use any [FPGA core that is available.

# Experiments Results

Bitumen is a brushable waterproofer sealant used on roofs. It hardens into a flexible rubber.

### Materials

• Bitumen Brushable Waterproofer - 500ml AU$8.64 • Graphite - Lock-Lube - 6g AU$ 6.11

### Results

• 10ml of bitumen and 750 mg of graphite. Result - >2M Ohms
• 10ml of bitumen and 1.25g of graphite. Result - 34k Ohms/cm
• 10ml of bitumen and 2g of graphite. Result - 500-1k/cm Ohms

### Notes

Additional graphite was added to the existing solution after the sample trace was drawn. At 2g of graphite the mixture was thick and difficult to mix and manipulate with a the toothpick I used to lay down the test trace. Paint thinner should be added to the mixture and tested.

### Theory View

Perhaps this is a good place to bring in a bit from the theoretical side of the matters. It may help to find out how close experimental results are to what might be possible with the ultimative fabricationg process.

#### Comparison by specific track resistance

Usually, electric circuits are made with copper traces and for wiring signals, these traces are pretty thin. Copper has a specific resistance of $1.68 \cdot 10^{-2}\ \Omega \cdot mm^2 / m$, while (pure) graphite has $8\ \Omega \cdot mm^2 / m$.

So, to replace tracks, you have to make tracks made from a material with higher specific resistance thicker. The rule is:

$Resistance\ per\ meter = \frac {specific\ resistance} {track\ thickness \cdot track\ width}$

For a copper track of 2 mil (which is pretty thin, but sufficient to forward a signal to the next chip) this is:

$R_S = \frac {1.68 \cdot 10^{-2}\ \Omega \cdot mm^2 / m} {35\ \mu m \cdot 2\ mil} = \frac {1.68 \cdot 10^{-2}\ \Omega \cdot mm^2 / m} {0.035\ mm \cdot 0.0508\ mm} = 9.45\ \Omega / m$

A replacement track made of graphite, 1 mm wide and 1 mm thick, has:

$R_S = \frac {8\ \Omega \cdot mm^2 / m} {1\ mm \cdot 1\ mm} = 8\ \Omega / m$

As one can see, replacing copper tracks with graphite is achievable.

#### Comparison by total track resistance

Now, to get a signal from one chip pin to another, the resistance of the track can be pretty high, as long as there is no (a neglibile amount of) current flowing. How much is possible there mostly depends on that required current, so you have to figure that out in single cases.

As most of our circuitry is digital, we have quite some allowance. If you apply 5 Volts on one side of the track and only 4 Volts are received on the other side of the track, this is still a valid "high" signal (for an ATmega running at 5 V).

## Impure Semiconductor Tests

### Materials

• Tanne Zinke 30+ SPF Zinc Oxide Sunscreen (425mg/g purity) AU$5.94 • Impure Copper Oxide made by cooking Copper Sulfate with Sodium Hydroxide • Richgro Copper Sulphate (Blue stone) AU$ 12.94
• Draino - Found under bathroom sink

### Results

• While making larger semiconductors do not require the purity or precision that is currently employed in the semiconductor industry to make the 5nm layers, less than 50% pure zinc oxide and sodium laced cupric oxide did not work.
• Experimenters should wait for the 99% pure compounds to arrive

# Future Experiments

## Diode

### Overview

The diode is one of the oldest application of semiconductor material. By taking an N-type material and joining it to a P-type material we create a gate that will only allow electrons to pass in a single direction. With a diode, a rudimentary AND and OR gate can be constructed.

### Expected Goals

• Validate that a diode can be constructed from semiconductor material suspended in extrudable materials.
• Determine the Voltage Drop across the diode.

### Instructions

Using powdered N-type and P-type materials each mixed with a small amount of cement, apply small dab of each on a non-conductive substrate so they are touching. Allow the cement to harden. Next add two conductive glue tracks, one track leading out of the p-type and one leading out of the n-type cement. While the glue is hardening, insert two metal wires.

## FET

### Overview

A Field Effect Transistor utilizes a magnetic field to control the flow of electrons through a thin N-type material channel on a p-type material substrate. The magnetic field is generated by a conductive plate over the n-type channel separated by a non-conductive insulator.

### Expected Goals

• Determine the feasibility of constructing a simple transistor through extrudable materials.
• Determine the Gate Voltage - depending on the final size, it is likely to be in rather high voltage (48V - 2kV)

### Instructions

Using powdered P-type material, mix with cement and create the P-type substrate. Create a rectangular base with two depressions on either side which will form the source and drain. Between the two depressions should be a wide shallow channel where the gate will be located. After the base hardens enough so it will not deform, fill the depression and channel with powered N-type material mixed with cement. Allow this to harden. Cover the gate section with an insulator - a very thin plate ABS/PLA material should work. After hardening, cover the insulator with conductive glue almost to the edge and use the glue to create the source and drain leads. Attach test leads to the source, gate and drain conductive materials to test.

## ALU

### Overview

Arithmetic Logic Unit is the heart of any micro processor. It is responsible for performing basic operations on multiple bits inside a computer. Examples of these operations would be AND, OR, XOR, ADD, SUB(tract), MUL(tiply), DIV(ide), LSR(Logical Shift Right), LSL (LS Left), LRL (Logical Roll Left), LRR (LR Right).

### Expected Goals

To validate that simple extruded gates can be connected together to produce a usable circuit

### Instructions

Awaiting results of FET test

## PIC

### Overview

A PIC micro controller is a popular small chip used control everything from washing machines to radio controlled cars.

### Expected Goals

Create a possible micro controller replacement for the electronics on the next generation of RepRap

### Instructions

Awaiting results of ALU test