printed circuit board

printed circuit board. A printed circuit board is a foundational platform used to mechanically support and electrically connect electronic components using conductive pathways, tracks, or signal traces etched from copper sheets laminated onto a non-conductive substrate. It provides the critical infrastructure for nearly all modern electronic devices, replacing the complex and unreliable point-to-point wiring of earlier systems. The design and fabrication of these boards is a core discipline within electrical engineering and is essential for mass production in industries from consumer electronics to aerospace.

Overview

The primary function of a printed circuit board is to provide a reliable structural base and an organized network of interconnections for components such as resistors, capacitors, and integrated circuits. This network is created by a process of etching the desired circuit pattern onto a copper-clad laminate. The widespread adoption of this technology was driven by the needs of the United States military for robust and reproducible electronics, particularly during the Cold War. Today, their use is ubiquitous, forming the core of devices manufactured by companies like Apple Inc. and Samsung Electronics.

Design and manufacturing

Design begins with schematic capture using Electronic Design Automation software from vendors like Cadence Design Systems and Mentor Graphics. This is followed by PCB layout and routing to define the physical placement of components and copper traces. Manufacturing involves multiple steps: laminating copper foil to a substrate, applying a photoresist, exposing it to ultraviolet light through a photomask, and then etching away unwanted copper. Key processes include electroplating for through-holes and the application of a solder mask and silkscreen for labeling. High-volume production is often handled by specialized firms in regions like Shenzhen.

Types and classifications

Printed circuit boards are categorized primarily by the number of conductive layers. Single-sided PCBs have copper on one side, while double-sided PCBs have it on both, connected by plated through-holes. Multi-layer PCBs, which can contain dozens of layers separated by insulating prepreg, are used in complex devices like central processing units. Other classifications include rigid PCBs, flexible PCBs (using materials like Kapton), and rigid-flex PCBs which combine both. High-density interconnect boards are essential for advanced microprocessor packaging.

Materials

The most common substrate material is FR-4, a glass-reinforced epoxy laminate defined by standards from the National Electrical Manufacturers Association. For high-frequency applications, materials with specific dielectric constant properties such as Rogers Corporation laminates or polytetrafluoroethylene are used. The conductive pathways are typically copper foil, while the protective solder mask is usually a polymer like photoimageable epoxy. Finishes to protect exposed copper from oxidation include electroless nickel immersion gold, hot air solder leveling, and organic solderability preservative.

Applications

Printed circuit boards are integral to virtually every electronic sector. In consumer electronics, they are found in smartphones, televisions, and personal computers. The automotive industry uses them extensively in engine control units and infotainment systems. Within aviation, they are critical for flight instrumentation and navigation systems. The medical device field relies on them for equipment like magnetic resonance imaging machines and pacemakers. They also form the backbone of telecommunications infrastructure, including routers and base transceiver stations.

History and development

The concept of printed wires on an insulating base was patented in 1903 by Albert Hanson in Germany. However, the modern printed circuit board was invented by Paul Eisler in the United Kingdom while working on radio sets around 1936, with significant use emerging in proximity fuzes during World War II. The technology was advanced by the United States Army Signal Corps and became commercially widespread in the 1950s after adoption by Bell Labs and IBM. The development of surface-mount technology in the 1980s, championed by companies like Sony, and the subsequent rise of ball grid array packaging, revolutionized board design and miniaturization, enabling the modern era of portable electronics.