What Are the Different Types of PCB materials?

Printed circuit boards or PCBs are the backbones of modern consumer and industrial electronics. They’re often hidden inside of protective cases, but they literally support our technological systems. But what are printed circuit boards?  What are the different types of PCB materials? And why have PCBs become one of the dominant technologies of our era?

What Is a Printed Circuit Board?

A printed circuit board contains a mix of conductive and insulating or dielectric layers. The circuit board that we see is generally created by etching exposed areas in the insulating layer to expose a conductor like copper underneath. Inductors, resistors, heat sinks and other components are soldered or connected to the printed circuit board.

Why Do We Use Printed Circuit Boards?

PCBs eliminated the tangled mess of wires that could literally get crossed or broken during use. Assembly of electronics was a time-consuming process, too, because of how long it took to connect all the wires. With PCBs, circuits are routed between various components via conductive traces on the surface or inner layers of the board. In many cases, no wires are required. Assembly is further simplified by the fact that the components are both glued down and connected to the circuit traces by the solder; commonly used for different types of PCB materials.

What Are PCB Layers?

In theory, the simplest printed circuit board has three layers. A conductive layer, generally made out of copper, is encased in two layers of strong, insulating dielectric materials like fiberglass. That outer layer is called the mechanical layer.

Printed circuit boards start with a fiberglass sheet. The conductive copper sheets are attached to each side. An etch-resistant wire pattern is printed on the copper sheet. All other copper is removed from the board. This creates the solid conductive tracing that will connect electrical components on the board. It is much faster to create than installing wiring, and it will be protected inside of the PCB layers. Solder mask is applied to the points where various components will be mounted. The copper trace may be exposed or covered over. It is possible to make PCBs with 10 or more layers, though this dramatically increases the cost. Drilling holes or even plating the through-holes is necessary to connect components with the inner layer of copper.

Depending on whom you ask, the solder mask used to attach the electrical components to the PCB is counted as a layer of the PCB. Applying it is certainly a step in the PCB assembly process. Silk-screening refers to the process of applying printed text and labels to the printed circuit board. This could be anything from a manufacturer’s mark to the labeling of components to aid in assembly and eventual repair of the board. Silk screening must be done after the laminated board layers are glued and heated to bind them together but before final finish or routing. The silk-screening step requires polyester screens stretched across the board. Then the special ink is sprayed on and cured. The polyester screens are removed and reused. However, not all PCBs go through silk screening. After all, you can laser etch the information into the PCB or simply apply a sticker with the manufacturer’s serial number to it.

How Many Different Types of PCBs Are There?

There are seven main types of printed circuit boards. The main categories of PCBs are defined by the number of layers and their degree of flexibility.

Single-sided PCBs or single-layer printed circuit boards have the simplest PCB design and simplest manufacturing process. The board has a single layer of conductive material. Components are only mounted on one side of the board. It is a straightforward assembly line process.

Double sided PCBs have a thin layer of conductive material like copper applied to both the top and bottom of the board. In general, one side is processed. Then the board is flipped and the other side is processed. The double-layer PCB may need to have holes in the board to connect components on both sides. This type of PCB costs a little more to make than single-sided boards, but it dramatically reduces the amount of space the PCB takes up. These boards are commonly used in industrial controls, cell phones, and UPS systems.

Multi-layered PCBs have by definition more than 2 layers. This means it has at least three conductive layers. They’re more difficult to design and manufacture. They’re commonly found in GPS systems, satellites, and servers.

A rigid PCB refers to any printed circuit board that cannot be bent or twisted. They may be single layer, double layer, or have multiple layers.

Flexible PCBs or flex circuits use a PCB material like polyimide to create a PCB that can be bent or folded. They can have any number of layers, but it is typically just one or two.

Rigid-Flex PCBs are flexible in some areas and rigid in others. The most common configuration has several flexible layers of the PCB mounted on a rigid PCB layer. It is often a composite material of sorts. This design is regularly used in automobiles, cameras, and cell phones. This reduces the risk of mechanical failure due to vibration.

Aluminum backed printed circuit boards are so different from the standard fiberglass and copper printed circuit board that it is considered its own product class. These PCBs generally have an aluminum core combined with standard FR-4. These PCBs are often the best choice for high power applications because it can dissipate heat so well. Aluminum PCBs can withstand much higher temperatures and stresses than fiberglass, as well. This is why they’re used in power supply controllers in car engines and AC/DC converters. The board still uses a copper layer, typically an electrolytic copper foil, to connect the electrical components. The aluminum substrate forms the main insulating layer.

What Are the Different Types of Material Used for PCB?

There are three main different types of PCB materials. The first is metal. Metals like copper, aluminum, and iron are generally used as the conductive layer in PCBs. Copper is the most popular. That is why most PCBs are “copper clad.” Every metal selected for use in PCBs supports the use of surface mount technology or SMT components. This is where you apply the solder mask to the metal traces and heat the board to solder the components into place. You can then do a quick quality check and test before sending the assembled PCB downstream.

The second type of material used in PCB manufacturing is PTFE or Teflon. It is a strong, lightweight, and somewhat flexible material. PTFE is preferred in applications with very tight tolerances because it doesn’t expand much on exposure to high temperatures. Another point in favor of this material is that it is flame resistant.

FR-4 is a glass-reinforced epoxy laminate sheet. It is a composite made of woven fiberglass cloth and a flame-resistant epoxy resin binder. FR-4 is the most commonly used material in printed circuit boards. Most of us have seen the green FR-4 board to which the electrical components are mounted, though it comes in other colors.

FR-4 is the NEMA grade designation for the material. FR itself stands for flame resistance. Most FR-4 boards have bromine in the epoxy laminate to help extinguish flames. FR-4 replaced G-10 boards in most cases, though G-10 will be used when thermal destruction is preferred. One point in favor of FR-4 is that it doesn’t absorb moisture. It is also very strong.

Polyimide can be used instead. It is a good choice for flexible and rigid PCBs. Polyimide costs more, but it is the ideal choice for flexible sensors and displays. They’re increasingly popular in tablet computers. Polyimides are thermally stable and can operate at temperatures of up to 260 degrees Celsius. They’re often good thermal conductors, as well. A similar but less commonly used material is PEEK for different types of PCB materials.

How Do I Choose a PCB Material?

Given the different types of PCB materials, how do you know which ones are best for your application? Be realistic. How much stress will the PCB be exposed to? How hot will it get? What is the safety margin? It is worth paying more for materials that will withstand higher temperatures and stresses if it prevents a plane crash or life-threatening failure in a medical device. This is why polyamides are being used in implants and prosthetics. The required electrical properties certainly affect the material you choose for the conductive layer.

It is possible to print flexible PCBs. These are finding their way into reusable medical devices and disposable sensors. In this case, you need something that is flexible, safe for use around patients, and doesn’t cost a fortune to produce.

Cost is always a factor, but it should be secondary to performance criteria. You can typically save money by choosing a material that meets the minimum performance requirements for your application. For example, cheap toys don’t need to meet the same exacting standards as a refrigerator motherboard. Safety regulations may require using a fire retardant in the epoxy or even prohibit the use of bromide in favor of another fire retardant, in case the PCB caught fire.

If you would like to learn more about printed circuit boards, don’t hesitate to reach out to the professionals at Geospace Technologies. Since 1980, we have stayed at the forefront of engineering and manufacturing innovation. Contact us or submit a form about your inquiry.