A printed circuit board (PCB) with a carbon film conductive pattern is created by coating the PCB substrate with carbon-based conductive ink, also known as carbon ink, and curing it. As a result of the market’s persistent decline in PCB board production prices, carbon oil keys are increasingly being used in place of the more costly gold keys. For both single and double PCBs, carbon oil board is a comparatively popular surface treatment technique. The PCB is capable of long-term reliable operation through a battery of testing, including aging tests and inspections, as well as other technical procedures.

Benefits of carbon ink PCBs

PCB laminates made of polyester, FR-4, FR-5, PTFE, polyimide, and carbon ink are among them. Resolutions as fine as 100μm trace width and spacing can be proposed by the carbon ink. Jumpers, LCD contacts, and keyboard connections are typically utilized with the carbon contacts on the carbon ink PCBs. For carbon widths, 75% of the nominal value is needed. The carbon contacts are usually round and have a diameter of 2, 2.5, 3, 3.5, 4, 5, 6, 7, and 8 mm.

Carbon Oil Ink

1. The constituents of carbon oil

Carbon powder, hardener, and synthetic resin make up the majority of carbon oil. Adhesion is aided by synthetic resin, which functions as a carrier. The function of the hardener is to cure.
A conductive role is played by carbon powder (graphite powder can be added, although it is expensive).
To increase conductivity and reduce resistance, some vendors dilute the carbon oil with a small amount of silver foil.

2. The carbon ink’s resilience

Square resistance is a common way to express carbon oil resistance. There are two types of ohms per square centimeter that are used: Ω/cm² and Ω/□. Today, most providers consent to using Ω/□.

The resistance value of any square carbon film on the other side is referred to as square resistance, and it is correlated with the carbon oil’s composition and thickness. One can examine it by looking at the figure below.

 

Carbon ink PCBs rules and guidelines

In line with Ohm’s law:

R=ρ*L/S, where L is the length of the carbon oil, S is the side area, and ρ represents resistivity. Thus, if L=m, R=ρ*L/r*m R therefore equals ρ*r. The formula above shows that “Ω/□” can be used to describe the surface impedance when it is L=W, or when the length and width are equal. However, it needs to be specified at what thickness the “Ω/₡” value is. Suppliers often indicate ≤ 30Ω/□ at 15um or 25um.

3. The management of carbon oil resistance

The content and thickness of carbon oil are the sole factors that affect its resistance. Thus, we need to consider three factors in order to have a resistance requirement that is sufficient.

  1.  A reasonable square resistance carbon oil that meets the process requirements.
  2.  After printing, a suitable thickness (0.01-0.025mm) ought to be attained.
  3.  Baked at a temperature of 150°C to 170°C for 30 to 60 minutes, or 150°C for 15 minutes in an infrared oven.

High temperatures, lengthy operating times, and low square resistance are all present throughout the actual operation process. Selecting an appropriate temperature and duration without compromising the substrate is crucial.

Factors influencing the PCB carbon ink production quality

1. Design

The conductive coating and inner layer of insulation are created by screen printing, while the conductive carbon ink PCB is produced by an additive technique. In order to provide the illusion of joining the circuit’s upper and lower layers, the connecting disks are stacked. In this manner, the process of producing it just requires the addition of two printed graphic layers to that of a single-sided circuit board.

2. Material Selection for Screen Printing

1) Choosing conductive carbon ink for the isolation layer of insulation

Jumper wires are supported and insulated by the printed insulation isolation layer. The product’s quality is immediately reflected in this layer’s quality. High insulation is the guiding criterion for choosing insulation layer ink. As a result, the phenolic system’s insulating layer ink is typically selected.

2) Choosing an Ink with Carbon Conductivity

Good conductivity and a lower coefficient of friction—which can be improved with longer friction times—are characteristics of carbon-based conductive ink. It also has a reduced surface contact resistance.

Select carbon ink as the primary ingredient. Particles of carbon ink resemble spherical colloidal particles in form. Strong adsorption is produced by graphitized carbon ink’s high carbon content, very low resistivity, high conductivity, and wide surface area for separation. Its dispersion improves as a result of its microscopic particles, which also lead to improved wear resistance, greater variable area, reduced resistance, and extraordinarily high conductivity.

3. Control of the production process

In terms of production process control, the main points to be noted are as follows:

  • Control of screen-printing process methods
  • Screen printing plate.
  • The effect of curing conditions on resistance
  • The impact of the punching process
  • The influence of the surface treatment process

Carbon ink PCB is a material made of high-purity graphite sintered at high temperatures, with very high strength and hardness. Compared with metal materials, carbon plates have higher strength and advantages in high-temperature and high-pressure environments.

Benefits of PCBs with Carbon Ink

Printing on PCBs with carbon ink is eco-friendly. It won’t contaminate the soil, water, or air. Carbon ink circuit boards also provide excellent durability at a reasonable cost.

  1. Flexible: Carbon ink printed circuit boards (PCBs) are particularly well-suited for applications requiring flexible circuit boards, such as wearable technology, sensors, and flexible electronic items since they can flexibly adapt to bending, folding, and unusual shapes.
  2. Low cost: Because carbon ink is a relatively inexpensive and simple-to-print substance, the manufacturing cost of carbon ink printed circuit boards (PCBs) is lower than that of typical copper foil circuit boards.
  3. Environmental protection: In compliance with regulations pertaining to environmental protection, the carbon ink ingredients used in carbon ink PCBs are usually non-toxic, innocuous, and biodegradable.
  4. Electromagnetic shielding: The carbon ink layer efficiently reduces electromagnetic interference and crosstalk due to its outstanding electromagnetic shielding ability.

Read More: PCB Standards and Heavy Copper Thickness 

Applications for PCBs using Carbon Ink

Applications for carbon ink PCB include RF shielding, automobile vehicles, keypads, remote controls, industrial engine control, calculators, phones, computers, TVs, and VCR typewriters. It is primarily used to provide a protected contact surface for switches.

One of the main factors influencing the reduction of PCB manufacturing costs is carbon ink, sometimes referred to as conductive carbon ink.

In terms of resilience, dried carbon ink is often sufficiently durable to bear over a million keystrokes on a keyboard or over a hundred edge connector insertions without exhibiting wear or increased resistance.

Characteristics of carbon ink

The three characteristics of carbon ink are its viscosity, thixotropy, and liquidity.

1. Viscosity

The internal friction of a liquid is called viscosity. It is also known as the liquid’s mechanical resistance among its many layers. In a thicker liquid than in a thinner liquid, its strength is always greater. It has been noted that viscosity is greatly influenced by temperature.

2. Thixotropy

The physical attribute of a liquid that allows it to regain its original viscosity or structure is known as thixotropy. It facilitates the liquid’s internal structural reconstitution. Screen printing is thought to work better using thixotropic ink.

3. Liquidity

The amount of outside force acting on ink is its liquidity. It is the most crucial component of printing. It is viscosity reciprocal. In order to provide even coverage across the copper button pads, carbon ink circuit surfaces need to have high printing qualities and good viscosity stability in warmer regions.

Screen printing is a straightforward process for printing carbon ink on PCBs. Engineers can save money on carbon ink PCBs because of the simple plating procedure and less expensive ink.

Conclusion

When it comes to flexibility, customization, and quick prototyping, carbon ink circuit boards are a revolutionary step forward in electronic design and production that standard rigid PCBs just cannot match. The future of electronics across industries is being shaped by the versatility of carbon ink circuit boards, which are being used in wearable electronics, medical devices, and Internet of Things applications. Even if there are factors like conductivity and durability, they can be efficiently addressed with careful design, skilled manufacture, and a full grasp of the advantages and disadvantages of the technology. Carbon ink circuit boards are a monument to the creativity that propels the electronics sector forward as technology advances.

FAQ’s

Why and Where to Use Carbon Ink Technology?

Printed circuit boards using carbon ink are frequently utilized in the following applications:

  •  Automobile Vehicles
  •  RF Shielding
  •  Keypad Keyboard
  •  Remote Controller
  •  Industrial Engine Control
  •  Welding Equipment

The use of rubber keypads, which are frequently used in garage door controllers and television remote controllers, is one area in which Carbon Ink PCBs shine. A standard conductive rubber keypad has a switching centre surrounded by angled webbing. The webbing stretches and responds tactilely when the switch is pressed. The webbing goes back to its neutral state as soon as the switch is not compressed.

How does it apply to PCB during manufacturing?

Carbon-based ink: A printed circuit board (PCB) that uses carbon ink as a conducting substance is referred to as a PCB. To form conductive traces or patterns on the PCB surface, carbon ink is a mixture of carbon particles and a binding agent. To achieve high-density wiring, conductive carbon ink designs are applied in one or two layers to a single-sided printed circuit board using a straightforward screen-printing technique. Printed conductive patterns find application in resistors, key switch contacts, electromagnetic shielding layers, and other applications that align with the current trend of electronic product shrinking, lightweight, and multi-functionality.

Why Us?

PCB Runner offers conductive carbon Ink manufacturing based on design requirements, we provide reliable & good quality circuit boards and can handle carbon paste/ink on surface pads. Submit your Gerber files at https://www.pcbrunner.com/free-pcb-quote/ or do reach out to our team offline at engineering@pcbrunner.com or sales@pcbrunner.com for your current or upcoming project’s needs.