Circuit Boards 101

What is a Circuit Board?

A circuit board, also known as printed circuit board or PCB, can be found inside every electronic device in today’s world.  In fact, the circuit board is considered the foundation of electronic devices because it is where the individual components are held in place and interconnected to make the electronic device work as intended.

Picture: Circuit board with green Solder Mask, without components (bare). 

In its simplest form, a circuit board is a non-conductive material with conductive tracks made of metal (usually copper) to physically support and electrically interconnect the components needed for an electronic device.

A design engineer working on a specific electronic device will create a custom pattern of electrically conductive tracks (called traces) with features like pads and holes where the components will be mounted onto and interconnected.  Since different devices require different components and interconnection to achieve the intended functionality, the pattern of copper tracks and conductive features on the substrate will vary from one circuit board design to another.

More complex circuit boards will have many layers of conductive copper tracks and interconnecting features sandwiched between non-conductive material.  With technology advancing and the demand for electronic devices to become smaller with increased functionality rising,engineers are pushing the boundaries of design and manufacturing capabilities to create circuit boards with finer features, higher numbers of conductive layers, and smaller and more densely packed components. These advanced circuit boards are often referred to as HDI or high density interconnect PCBs. To learn more about HDI PCBs, click here.

What Are Circuit Boards Made Of?

The most common non-conductive material used to support the etched copper tracks and conductive features in a circuit board is a composite material made of woven fiberglass cloth and epoxy resin. Surprisingly, this material is usually an off-white color, not green. The green color (or any other color) is added later as one of the final steps in the circuit board manufacturing process. This added layer of color is called Solder Mark and is used to protect the top and bottom layers of copper which would otherwise be exposed.

Although the common substrate made of fiberglass and epoxy resin is adequate for many electronic devices, it may not be for others since not all devices are made for the same purpose, application, or environment. Many electronic devices require that the PCB substrate meet certain properties, and therefore, demand a more advanced or specialized type of substrate. These requirements can include a certain level of temperature resistance, shock resistance, and brittleness just to name a few, but the list of properties and qualifications can be extensive. Click the link to learn more about the different types of materials available for circuit board manufacturing.

Manufacturing Circuit Boards

Picture: Bare circuit board array with 0 and 90 degree score lines.

As PCB fabrication technology evolves, it has become cheaper, faster, and more convenient to have printed circuit boards professionally fabricated.  Most PCB manufactures require Gerber files to manufacture circuit boards, which contain the data, drawings, and specifications for a particular circuit board design to be produced.

PCB design automation software such as AdvancedPCB’s PCB Artist® enables design engineers to layout their circuit board design according to their needs and requirements to later export that data for their circuit board manufacturer.  The manufacturer uses the electronic data and fabrication drawings to set up automated equipment to produce the circuit boards with matching specifications and features.

Where Are Circuit Boards Used?

Today it would be easier to answer where circuit boards are NOT used. Nearly every electronic device now incorporates PCB technology for one or many different functions.

Automobiles – PCBs abound in many aspects of the computerization of vehicles, from ignition systems to keyless entry to the many safety sensors throughout the engine and passenger compartments.

Aviation – lightweight and high-performance circuit boards are essential to the design and operation of aircraft, including communication and guidance systems. Technology used in drone construction is facilitated through the use of small, lightweight PCBs.

Smartphones – without the complex and miniaturized PCBs developed for communications devices, the smartphones, fitness devices, and wearable technology in such demand by consumers would not be possible.

Home automation – smart thermostats, home surveillance systems, and smart appliances make effective use of printed circuit boards. Taking a quick inventory of any home will reveal an abundance of circuit boards in residence.

Entertainment – flat-screen televisions could not even exist if wiring and tube technology were not replaced with high-density, high-performance circuit boards. MP3 players and sophisticated commercial and home entertainment systems rely heavily on the use of printed circuit boards, as well.

Toys – yes, even many simple children’s toys incorporate PCB technology for generation of sounds, flashing lights, and movements.

How Did Circuit Boards Evolve?

From the initial post-WWII days of the first operational PCB, materials, construction methods, and technology have made tremendous progress.

In the 1950’s through 1960’s, materials continued to evolve, and a team of scientists working with the US Army received a patent for a new process for creating circuit boards. This process included drawing the pattern for wiring and photographic it on a zinc plate, which could then be utilized on an offset printing press to print the wiring in acid-resistant ink on copper foil. The foil could then be etched utilizing an acid solution, leaving the desired wiring pattern.

The 1960’s also saw the advent of PCBs being designed and manufactured utilizing multilayer technology in excess of four layers.

Double-sided boards came into use as enhanced plating processes were developed that allowed hole walls to be plated, with the 70’s also seeing the beginning of board size reductions and hot air soldering.

Throughout the 90’s the demand for complexity of circuits and the off-setting growth in PCB technology have contributed to capabilities hardly imaginable just short years ago.

What’s New in Circuit Board Technology?

Today’s design and manufacturing techniques contribute to the growth in PCB manufacturing capabilities and demand. Integration into devices that require miniaturization of circuits and high reliability are common-place today:

• Healthcare – diagnostic and monitoring devices have made enormous advances in the quality of healthcare, and the very quality of life for patients with embedded appliances such as pacemakers, defibrillators, and internal medicine pumps.

• Communications – constant growth in demand for personal communication devices as well as the Internet of Things (IoT) ensures long-term growth potential for devices that enable consumers quick and easy communication.

• Aerospace – even the earliest space mission contained circuit boards, but today’s exploration and space missions make significant use of complex, light-weight, highly-functional PCBs. Similarly, commercial and military aircraft incorporate an abundance of sophisticated electronics for navigation, communications, and even for passenger entertainment and connectivity, all made possible through the use of PCBs.

Significant advances in the design and fabrication of PCBs include:

HDI – high density interconnect boards – capability to produce boards with more components in less space, resulting in high-performance, reduced space and weight, and higher reliability.

LDI – Laser direct imaging – a much more precise method of creating the design image on PCB materials, replacing the less accurate and constraint-burdened photochemical process.

Flex PCBs – materials and fabrication techniques that permit flexibility in circuit boards to accommodate application-specific requirements.

Software Enabling Circuit Board Technology

One of the key factors in the continuing evolution of circuit board technology is sophisticated software development tools. Computer aided design and manufacturing (CAD/CAM) programs available to designers and manufacturers contribute greatly to efficiency and minimizing the time from concept to market.

Programs now exist for detailed PCB design and layout, generation of files for manufacturers, and the actual fabrication process. Designers are now able to collaborate with vendors more effectively, streamlining the development process. Software available to PCB designers can also check design files for missing or incomplete information, before they are submitted to the manufacturer.

Click the links below to learn more about printed circuit boards & PCB manufacturing:

• Learn more about PCB manufacturing
• Learn more about PCB Assembly
• Learn more about PCB fabrication capabilities