What is a Printed Circuit Board?

What Is a Printed Circuit Board (PCB)? Its Role and the Difference from a Printed Wiring Board

A printed circuit board is a board-shaped insulating substrate with conductive wiring formed on or within the substrate. The terms printed circuit board (PCB) and printed wiring board (PWB) are commonly used in the electronics industry.
KAKEN TECH develops and manufactures flux cleaning systems for removing flux residue remaining after electronic components are soldered to PCB pads and terminals.
This page explains the basics of printed circuit boards, which are closely related to electronics assembly and flux cleaning.

	PCBs are normally hidden inside electronic devices and electrical products, but the familiar green board found inside many electronic products is a typical example. In this article, the term PCB is used broadly for boards that provide electrical interconnections and serve as the platform on which electronic components are mounted.
	For simplicity, this page mainly uses “PCB” when explaining board types, structures, materials, and manufacturing processes before component assembly.

PCB Structures: Single-Sided, Double-Sided, and Multilayer Boards

Printed circuit boards can be classified according to the number of conductive circuit layers.

Single-Sided PCB

Cross Section
Typical Applications	Cost-sensitive, high-volume consumer electronics and other relatively simple electronic products
Description	A PCB with a conductive circuit formed on only one side of the base material.

Double-Sided PCB

Cross Section
Typical Applications	Consumer electronics, industrial equipment, and a wide range of other electronic products
Description	A PCB with conductive circuits formed on both sides of the base material. It enables higher wiring density than a single-sided PCB and is widely used as component integration and product functionality increase.

Multilayer PCB

Cross Section
Typical Applications	Industrial electronics, mobile consumer electronics, and other applications requiring compact size and high-density interconnection
Description	A PCB containing three or more conductive circuit layers, including inner layers and outer surface layers.

Common PCB Materials and Their Characteristics

A wide variety of PCB base materials are used according to application requirements such as heat resistance, high-frequency performance, reliability, mechanical properties, and cost.

Representative PCB materials include the following.

Paper Phenolic PCB

Paper phenolic boards use paper impregnated with phenolic resin.
Compared with higher-performance laminate materials, they generally have higher moisture absorption and more limited electrical and thermal performance, so they are mainly suited to cost-sensitive applications with relatively moderate requirements.
They have traditionally been used in consumer products, toys, educational electronics, and hobby applications.

Glass Epoxy PCB

Glass epoxy boards use glass-fiber reinforcement impregnated with epoxy resin. FR-4 is a widely used classification of glass-reinforced epoxy laminate.
These materials provide a useful balance of electrical insulation, heat resistance, mechanical strength, dimensional stability, and manufacturing compatibility, and are widely used for multilayer and high-density PCBs.

Ceramic Substrate

Ceramic substrates use electrically insulating ceramic materials such as alumina. They can provide high heat resistance, electrical insulation, dimensional stability, and comparatively high thermal conductivity.
They are used in applications requiring heat dissipation or high reliability, including certain power and electronic modules.
Because manufacturing cost and mechanical characteristics differ significantly from organic laminate PCBs, ceramic substrates are selected for applications where their specific properties are required.

Metal-Core PCB

Metal-core PCBs use a metal base, such as aluminum or copper, together with an electrically insulating layer and conductive circuit layer.
The metal base helps transfer heat away from components, making these boards useful for power electronics, LED applications, and other assemblies requiring improved thermal management.

Flexible Printed Circuit (FPC)

Flexible printed circuits use thin flexible insulating films such as polyimide or polyester as the base material.
Because they are thin and lightweight, they are used in compact and lightweight electronic devices and modules. Their flexibility also makes them suitable for wiring through moving, folded, or curved sections of a product.

How Printed Circuit Boards Are Manufactured

Printed circuit boards are generally manufactured through a series of patterning, lamination, drilling, plating, surface finishing, and inspection processes.

The following example summarizes a typical multilayer PCB manufacturing flow.

Inner-Layer Pattern Formation		Circuit patterns are formed on copper-clad inner-layer material using processes such as imaging and etching.
Lamination Pressing		Inner-layer cores and prepreg insulating layers are stacked and laminated under heat and pressure to form the multilayer structure.
Drilling		Holes are drilled in the laminated board using drilling equipment or other processes according to the board design.
Through-Hole Plating		The hole walls are metallized and plated to create electrical connections between conductive layers.
Outer-Layer Pattern Formation		Circuit patterns are formed on the outer surfaces of the PCB.
Solder Mask and Legend Printing		Solder mask is applied to protect designated circuit areas, followed by legend or symbol printing as required.
Surface Finish		A suitable surface finish is applied to exposed copper pads to protect solderable surfaces from oxidation and contamination before assembly.
Profiling		The PCB panel is routed, punched, or otherwise separated into the required board outline.
Inspection		Electrical performance, dimensions, and appearance are inspected according to the required specifications.

High-Frequency PCB Requirements and Flux Cleaning

	Modern communication and sensing systems increasingly use higher-frequency signals, including frequency bands used by 5G communications and automotive radar. At higher frequencies, PCB material properties, transmission-line design, conductor geometry, surface roughness, and manufacturing quality can have a greater effect on signal loss and signal integrity.
	For high-frequency PCB design, low-loss dielectric materials and appropriate circuit design are important. In assemblies where flux residues could affect electrical characteristics, contamination control and flux-residue removal may also be considered according to the circuit design, flux chemistry, operating frequency, cleanliness requirements, and reliability targets.

Reference

Standard Micro-Soldering Technology, 3rd Edition
Edited by the Micro Soldering Education Committee, Japan Welding Engineering Society
The Nikkan Kogyo Shimbun, Ltd.

Related Articles & Products for PCBs and Flux Cleaning

	Technical Solutions What Is Flux Cleaning? Explains the purpose of removing flux residue generated during soldering in electronics assembly, together with representative cleaning methods and key considerations for efficient cleaning.
	Published Technical Article Technical Information: Flux Cleaning An article on flux cleaning covering the evolution and purpose of flux cleaning and cleaning technologies used in electronics assembly.
	Product Information MICRO CLEAN and MARKLESS$00AE Flux Cleaning System KAKEN TECH offers a flux-cleaning system combining MICRO CLEAN cleaning agents with MARKLESS rinsing agents for electronics cleaning applications.