Printed circuit boards are arguably the most ubiquitous technology in use today. They are present in practically every modern device, including remote controls, computers, smartphones, vehicles, music players, smartwatches, airplanes, industrial machinery, and so much more. Printed circuit boards look simple, appearing on their own as thin boards with patterns. However, they are the heart of modern electronics and perform a very crucial task.
Electronic devices and machines function using complex circuits that comprise numerous electronic and electrical components. Printed circuit boards serve to mechanically support and electrically connect all the various components that make up a circuit in a device in a compact, neat, and efficient manner. They are made up of a flat sheet of insulating material, called the substrate, laminated to a highly conductive material, the most commonly used being copper.
Predetermined patterns are etched out of the copper layer through a photochemical process, creating separate conducting lines known as tracks or traces, pads, vias, and other electrically conductive geometric shapes that each have specific functions. The tracks serve as the wires in the circuit, while the pads serve as connection points for the components that will make up the circuit. Other etched features such as vias and solid conductive areas are used to interconnect multiple layers on a multilayer board and for electromagnetic shielding, respectively. The etched features are separated and insulated from each other by the substrate material. After the board has been manufactured, the components are attached to it by soldering.
In addition to the copper and substrate layers, printed circuit boards typically feature a protective layer of solder mask and may feature a silkscreen.
History of Printed Circuit Boards
Considering their importance and vast usage in modern electronics, it’s not out of place to wonder how technology existed before printed circuit boards. Circuits were widely used in various devices long before the invention of these boards. However, buying circuit boards were built by connecting components together via wires, in a method known as point-to-point connection. The wires were often soldered to the leads of the components to accomplish conductive paths. It was also common practice to directly connect components that could be placed close to each other by their leads.
Another popular method was wire wrapping. In this method, electronic components were placed on an insulating board and interconnected with insulated wires. The ends of the wires were stripped and wrapped continuously around socket pins or leads.
While these methods were manageable for small circuits, larger circuits comprising numerous components required so many wires that they ended up as a disorganized bundle of wires and components. This reduced the efficiencies of the circuits and made testing and debugging a very tedious process. In addition to these difficulties, manufacturing electronic devices was a slow and tedious process, as numerous components had to be manually connected and soldered.
Fortunately, printed circuit boards, a faster, more compact, neater, and far more efficient alternative have been developed. The history of printed circuit board technology as we know it began in 1903 when Albert Hanson, a German inventor, filed a British patent for a flat foil conductor on an insulating board with multiple layers. That was the first ancestor of printed circuit boards. Over the years, several significant developments and improvements have taken place to arrive at the highly efficient tech that is widely used today.
Printed Circuit Board Design
The patterns etched on a printed circuit board are not random. The design to be printed is known beforehand. Every printed circuit board is manufactured to connect and support a particular circuit, and so all the tracks, pads, vias, etc., are calculated and designed in advance. PCB design is a thorough and meticulous process that is considered both a science and an art. It must be done right for the functionality and reliability of the board. PCB design involves the following essential steps.
- Planning: Before anything can be done, the function of the circuit has to be determined. In this step, the various electronic components that are required to work together in a circuit to perform said functions would be identified.
- Drawing: After planning the circuit, an electrical/electronics engineer draws a detailed circuit outline, connecting all the different components. The drawing, also known as a schematic, is of a fully functional circuit. However, at this point, the components aren’t arranged exactly as they would be on the printed circuit board.
- Testing: This step involves procuring the real-life components and, using the circuit schematic as a guide, connecting them into an actual circuit. This can be done on a prototype board that can also test the circuit’s functionality.
Learn more about prototype boards and circuit prototyping
- Design: Printed circuit board design is a crucial step in printed circuit board manufacturing. In this step, designers use special PCB design software to carefully layout and organize the circuit’s components on a virtual board, using the schematics created and tested in steps 2 and 3. The virtual board is given specific outline dimensions as required and is an exact virtual replica of the real-life printed circuit board. Every track, pad, via, and component is virtually placed to get the required pattern that would later be printed. After designing the board, the design file is exported and sent to the manufacturer for fabrication.
These design tips are essential when designing a printed circuit board.
In addition to identifying the function and required components of a circuit and creating the board pattern, printed circuit board design also involves considerations such as the application of the board, operating environments, available space for installation, and board type. All these considerations significantly impact manufacturability, operation coats, lead times, and production speed.
Printed Circuit Board Terminology
Some specific words and phrases are commonly used in the world of printed circuit boards. It is important to familiarize yourself with these words if you intend to work with PCBs.
- Annular Ring: The area that is left of a copper pad after a hole has been drilled through it for surface mounting is called the annular ring.
- ESD: Commonly known as Electronic static discharge, which is caused by static electricity.
- Gerber File: A Gerber file is a standard CAM file that informs the manufacturer how the board is to be printed.
- Lead: This refers to the terminals of a component.
- Mil: A Mil is the value of a thousandth of an inch.
- Node: This is a lead or pin that has been connected to a wire.
- Short: This is a short form of the term “short circuit,” which occurs when there’s excess current in a connection point.
- Via: Vias are copper plated holes that run through the layers of multilayer boards to provide interconnectivity.
Printed Circuit Board Materials
A printed circuit board doesn’t comprise just the substrate and copper layers. Additional layers, such as the solder mask and the silkscreen, serve to enhance the board. All these layers are made of different materials with specific characteristics.
Copper is widely used to create the conductive layer of printed circuit boards due to its high electrical conductivity. It is usually laminated to an insulating substrate and provides the conductivity of the board. The electronic components are placed directly on the traces and pads etched out of the copper layer.
The substrate serves to separate and insulate the traces and pads from each other. A printed circuit board can, in fact, be described as copper lines and shapes running along the surface of the substrate. Various materials are used as substrates. The most ubiquitous of these is FR4, a glass-reinforced epoxy laminate material. FR4 is used in rigid boards. Other substrate materials used are polyamide fiberglass and phenolic resin-impregnated cotton paper. Plastic substrates such as polyester, polyethylene naphthalate, and liquid crystal polymer are used for flex boards.
Soldermask is a layer of liquid epoxy that is usually applied to a printed circuit board’s exterior layers. Soldering is the most commonly used process for attaching components to a board. During soldering, the solder temporarily becomes liquid, gaining the ability to flow. The solder mask controls and retains the solder’s flow during soldering to prevent it from flowing out across the board’s layer, as this can connect adjacent circuits, leading to shorts on the board.
The silkscreen is not vital to a printed circuit board’s performance. However, it plays an important role in certain applications. The silkscreen is an ink trace layer printed along with labels, legends, and texts that may be required for identification or information purposes.
Printed Circuit Board Components
The numerous components that populate a printed circuit board are either interconnect devices or circuit components
Devices often have more than one board. The boards work together to perform the overall functions of the devices. It is also often necessary to connect printed circuit boards to other devices or external boards. This interconnectivity is achieved using interconnect devices.
- Edge connectors: Edge connectors are usually located at the edge of a printed circuit board and are designed to plug into a matching socket. The male connector, printed at the board’s edges, is connected to a female connector that contains both a socket and a varying number of outward pins. The assembly can then be plugged into a matching socket of another device.
- Ribbon cables: Ribbons cables are flat, wide cables that are made up of several small cables arranged parallel to each other. One or both ends of cables are mass terminated and attached to an IDC (Insulation Displacement Connector). There are numerous types of connectors (male/female, number of pins, etc.) that can be attached to ribbon cables. These determine the method by which the cable can be connected to a printed circuit board.
- D-Connectors: D-Connectors comprise multiple parallel rows of pins or sockets encased in a D-shaped metal shield, hence the name “D-connector.” The metal shield mechanically supports the connector and prevents electromagnetic interference. The pins of a D-Connector are directly soldered to a printed circuit board and are typically mounted at a right angle to the board to allow a cable to be plugged into the edge of the assembly.
- Rectangular connectors: These are rectangular, male or female connectors that are mounted on a printed circuit board to allow female or male devices to be connected to the board.
- IC sockets. IC chips can be soldered directly onto a printed circuit board. However, certain applications, such as prototyping, may require an IC chip to be removable. For such applications, IC sockets are used. The IC socket is soldered onto the board, and the chip can easily be attached and removed for reprogramming.
When components have been mounted on a printed circuit board, it’s referred to as a printed circuit board assembly. The components work together to execute the intended circuit function, with the printed circuit board providing interconnectivity.
Numerous electrical/electronic components are employed to achieve various circuit functions. The following are the most commonly used of these.
- Resistors: These components are used to control the flow of electric current or to cause a drop in voltage. These components restrict the flow of current and come in different levels of resistance.
- Capacitors: Capacitors perform many functions. They store electrical energy and restrict the flow of DC (Direct Current) while allowing the flow of AC (Alternating Current). Decoupling capacitors are also used to filter or minimize noise.
- Diodes: Diodes are electrical components that can control the flow of electric current to a particular direction while blocking current in the opposite direction. They are made of semiconductor material.
- Transistors: Also made from semiconductor materials, transistors serve to either amplify the current flowing through it or switch the direction of the current’s flow.
- Inductors: These components block fluctuations in alternating current while direct current flows through them. They are also called chokes or coils.
- Switches: Switches are able to block or allow the flow of current, depending on whether they are open or close.
Types of printed circuit boards
There are various types of printed circuit boards that each have specific functions, benefits, and limitations. These boards are classified according to a number of characteristics.
According to the number of copper layers they have, printed circuit boards can be classified into single-sided (single layer), double-sided (2-layer), and multilayer.
Also known as single-layer boards, single-sided boards are made up of one layer of copper, laminated to a substrate layer. These boards may also feature a solder mask and a silkscreen. PCB cost for single-sided boards are easy to design and cost less to mass-produce. However, they are only suitable for the most simple of circuits.
Double-sided or 2-layer boards feature a layer of substrate sandwiched between two layers of copper. Components can be mounted on both sides of the board. Double-sided boards may feature holes through which the leads of components can be inserted and soldered on the other side of the board. These boards can be used for relatively simple circuits.
These boards feature four or more layers of copper, laminated to alternating layers of substrate. The different layers usually have dedicated purposes and are interconnected by vias. For example, a multilayer board may have signal layers, ground layers, and supply planes. Multilayer printed circuit boards are more expensive to make but are great for complex circuits, RF components, and specialization applications.
Printed circuit boards can also be classified by their bendability, as rigid, flexible, and rigid-flex.
Rigid printed circuit boards are constructed using rigid fiberglass substrates, making it impossible for them to bend. While they are easier and cost less to manufacture than their flexible counterparts, rigid boards are less versatile and can’t fit into complex spaces. The majority of all boards manufactured and in use today are rigid. Rigid boards are available as single-sided, double-sided, and multilayer boards.
Flexible printed circuit boards feature bendable plastic substrates, making them highly flexible. They are light and can be folded and twisted to fit into complex spaces. Flexible boards can also be manufactured to be shockproof, heat resistant, waterproof, and corrosion-resistant. However, they are more difficult and expensive to manufacture than rigid boards. Flexible boards are also available as single-sided, double-sided, and multilayer boards.
Rigid-flex boards combine the desirable qualities of both flexible and rigid boards. They comprise portions of flexible boards attached to portions of rigid boards. Some of the combined advantages of rigid-flex boards over the other individual boards include a lower part count, more streamlined design, and reduced board size and weight, as the electronic connections are buried inside the board.
Printed Circuit Board Assembly Components
There are two common methods for assembling components to a printed circuit. They are surface mounting and thru-hole mounting.
In surface mounting, small components are placed directly on the exterior of the board and soldered in place. In thru-hole mounting, on the other hand, the board has pre-drilled holes. The leads of large components are inserted into these holes and soldered on the other side of the board.
Applications of Printed Circuit Boards
Printed circuit boards have become indispensable in modern technology. These devices are widely used in various applications across numerous industries. The following are a few of the multiple applications of printed circuit boards.
Computers are highly functional devices capable of carrying out complex applications. A computer is made up of hundreds of board-mounted circuits that work together to execute tasks. The motherboard, which is the heart of a computer, is, in fact, a printed circuit board assembly. Other well-known computer components such as RAM and video cards are all PCBAs.
More and more military systems and equipment are integrating advanced computerized technology for higher accuracy and efficiency. Printed circuit boards are widely used in these technologies. Because of their ruggedness, flexible and rigid-flex boards are especially beneficial in heavy impact, shock, and vibration applications. These include military vehicles and modern weapon systems.
Aerospace is one of the most demanding industries on circuit board development. The need for very high accuracy, efficiency, and compactness is responsible for the vast application of printed circuit boards in aerospace. Thousands of printed circuit board assemblies can be found in satellites, drones, aircraft, etc.
Medical devices such as radiation equipment, MRI machines, medical computers, pacemakers, hearing aids, and so many others all employ printed circuit boards. They have led to the development of complex, compact, highly functional medical devices.
Because of their ease of customization and relatively low manufacturing costs, printed circuit boards are excellent for DIY projects. You can simply plan a circuit, design the board layout, and forward the design files to a printed circuit board manufacturer for printing.