A comprehensive guide to printed circuit boards (PCBs)

Printed circuit boards are fundamental components of smartphones, computers, household appliances, and advanced medical devices. In the article “Comprehensive Guide to Printed Circuit Boards (PCBs),” we will cover the construction, materials, manufacturing processes, and various types of PCBs, as well as the standards and technologies used in their production. Through this guide, you’ll gain a comprehensive understanding of what PCBs are and how they function.

Printed Circuit Boards (PCBs) are the physical foundation on which electronic components are mounted, enabling their electrical connections. It is important to note that a PCB is not just a physical base but also serves as a conduit for routing electrical signals between components. Without PCBs, devices like smartphones, computers, washing machines, and advanced medical devices would not be able to function. PCBs provide mechanical stability, precise electrical connections, and facilitate the miniaturization of modern devices, making them essential in various fields of electronics.

Construction and materials of PCBs

Manufacturing PCBs requires various materials and structural components to ensure their functionality and durability.

1. The PCB substrate is typically made from an insulating material that provides both mechanical support and electrical insulation. The most commonly used material is fiberglass-reinforced epoxy laminate (FR4), which is the most popular choice for rigid PCBs due to its excellent mechanical and electrical properties. Another such material is polyamide (PI) or polyimide, which is used in flexible PCBs, providing greater flexibility and resistance to high temperatures.
2. Copper layers form the conductive paths on a PCB. One or more layers of thin copper are placed on the substrate, which are essential for the functioning of electrical circuits. The thickness of the copper layers can vary depending on the requirements of the PCB design and application.
3. A solder mask is a protective layer, usually green, that is applied to the surface of a PCB. It protects copper tracks from oxidation, corrosion, and accidental connections during the soldering process. The solder mask also helps to accurately place solder only on the intended areas.
4. The silkscreen is located on top of the solder mask and contains component descriptions, symbols, and other markings necessary for PCB assembly and diagnostics. This is a crucial element that facilitates component identification and improves the readability of the entire circuit.
5. Vias are metallized holes in PCBs that allow connections through different layers of tracks in multilayer PCBs, enabling the routing of signals and power between layers.

PCB manufacturing process

PCB manufacturing involves several stages:

1. PCB design is performed by engineers using CAD software to create the layout of tracks and place components on the board.
2. Pattern creation involves shaping a layer of copper on the substrate through photolithography or printing. This process allows for the precise mapping of paths according to the CAD design.
3. Etching is the chemical removal of excess copper, leaving only the designed paths on the board. This ensures that the conductive paths are in accordance with the design.
4. Hole drilling is the step where holes are made for vias and the mounting of components. The metallization of these holes enables the connection of tracks on different layers of the board, ensuring proper electrical connections. The hole metallization process includes both chemical and electroplating methods. In the chemical process, the holes are coated with a thin layer of copper through chemical deposition. Then, in the electroplating process, this layer is thickened by electrochemical copper deposition, ensuring proper conductivity and mechanical strength.
5. Solder mask application is a process in which a protective layer is applied to the board to protect the tracks from oxidation and accidental shorting. Printing is then applied to identify the component mounting locations.
6. Assembly and soldering of electronic components on PCBs. This process ensures the functionality and permanent electrical and mechanical connection of the components to the board.
7. Programming of electronic circuits occurs after the physical assembly of components, enabling them to perform specific functions. This process includes using specialized software and interfaces to insert code into the memory of integrated circuits, allowing them to function as intended.
8. Testing is the final stage of PCB production. It involves checking whether all paths, connections, and components are functioning correctly.

Operation of PCBs

PCBs deliver electricity to electronic components through copper paths that efficiently carry current from the power source to processors, memory, and other integrated circuits, ensuring minimal energy loss and power stability. They effectively enable signals to be transferred between components, minimizing electrical interference and noise. PCBs also act as structural support for components, ensuring their stability and durability through soldering. Multilayer PCBs contain insulating layers, preventing short circuits, and protective coatings to guard against corrosion and damage. They also help dissipate heat generated by components, acting as a heat sink. PCBs enable the integration of multiple functions into a single device, allowing the creation of complex systems that perform a variety of tasks.

Types of PCBs:

1. Single-layer PCBs have one layer of copper on one substrate and are used in simple electronic devices.
2. Dual-layer PCBs have a layer of copper on both sides of the substrate and are used in devices of medium complexity.
3. Multilayer PCBs consist of three or more layers of copper and are used in complex devices such as computers and cell phones.
4. Flexible PCBs are made of materials that can be bent and molded. They are used in wearables and many other applications where flexibility is required, such as in aerospace, medicine, and custom-shaped devices like hearing aids.
5. Rigid-flexible PCBs are a combination of rigid and flexible segments, used in electronic devices where both rigidity and flexibility are required, such as advanced medical devices and military equipment.
6. Metal-core PCBs (MCPCBs) contain a metal core for dissipating heat and are used in devices handling high currents, such as LED lighting and power devices.
7. High-frequency PCBs are made of materials that allow operation at high frequencies, used in telecommunications and radio systems where minimal signal loss is required.
8. HDI (High-Density Interconnect) PCBs are characterized by high-density interconnections and are used in advanced electronic devices such as smartphones. HDI PCBs often utilize microvias, which are small, precision-drilled holes used to connect layers. This technology enables the creation of more complex circuits on smaller surfaces. The process of creating microvias often involves the use of lasers, allowing for accurate and repeatable drilling of the holes.
9. PCBs with embedded components integrate these components into their layers and are used in compact technology devices.
10. Optical PCBs have pathways for transmitting light signals and are used in advanced communication systems.

Standards and norms

PCB production is subject to numerous standards and norms that ensure quality, safety and environmental compliance.

• International organizations, such as the IPC (Association Connecting Electronics Industries), standardize the quality and processes involved in PCB manufacturing. IPC standards define the quality criteria that PCBs must meet to ensure their reliability and compliance with customer requirements.
• The European Union’s RoHS (Restriction of Hazardous Substances) directive restricts the use of hazardous substances in electronic equipment, such as lead, mercury and cadmium. RoHS aims to protect human health and the environment by reducing hazardous electronic waste. This directive requires PCB manufacturers to use materials that do not contain these substances, which is key to ensuring environmentally friendly production and user safety.

Contemporary challenges and technologies

Contemporary challenges and technologies:

1. EMI (Electromagnetic Interference) requires careful design of paths, shielding, and the use of ground and return layers. Additionally, interference suppression filters and components are applied.
2. Heat dissipation is crucial in high-density component PCB designs. It requires effective thermal management, which includes the use of heat sinks, embedded thermal conductive materials such as metal cores, and the design of thermal vias and vents.
3. High-density integration requires advanced techniques such as HDI (High-Density Interconnect), microvias, embedded components, and the use of thin dielectric layers, allowing more connections to be packed into a smaller area.
4. Miniaturization and reliability in modern technologies, such as IoT, wearables, and automotive applications, require increasingly advanced and reliable PCBs. This necessitates precise assembly of SMD (Surface-Mount Device) components, the use of flex and rigid-flex technologies, as well as rigorous testing and certification for durability and reliability.
5. The use of new materials, such as low-loss laminates for use in high-frequency applications, as well as materials with a low coefficient of thermal expansion (CTE).

Why choose Device Prototype for your PCB projects?

Today’s challenges in PCB design, manufacturing, and assembly demand not only advanced knowledge but also access to modern technologies and innovative solutions. Device Prototype fulfills these requirements by offering comprehensive services in electronic device design and prototyping, including circuit assembly. With our experience and professionalism, we provide support at every stage of PCB development—from concept, through design and production, to the testing of finished prototypes.