I. Introduction

A PCB (printed circuit board), also known as a printed circuit board or printed wiring board, is commonly referred to simply as a "printed board." In English, it is abbreviated as PCB (printed circuit board) or PWB (printed wiring board). Made from an insulating substrate and cut into specific dimensions, a PCB features at least one conductive pattern etched onto its surface, along with various holes—such as component holes, fastening holes, and plated-through holes—that serve to replace the traditional chassis used for mounting electronic components and enable electrical connections between these components. Because this type of board is manufactured using electronic printing techniques, it is called a "printed circuit board." It is technically inaccurate to refer to a "printed wiring board" simply as a "printed circuit," since the board does not actually "print components"—it only contains wiring traces.

II. Basic Components

The current circuit board is primarily composed of the following:

1. Traces and Pads (Patterns): Traces serve as the conductive pathways between components. In the design, a large copper plane is separately designed for the ground and power layers. Traces and pads are created simultaneously.

2. Dielectric Layer: Used to maintain insulation between circuit traces and various layers; also known as the substrate.

3. Holes (Through holes / vias): Through holes enable electrical connections between layers of circuitry. Larger through holes are used for component insertion. Additionally, non-plated through holes (nPTH) are typically employed for surface-mount positioning and as fixing points for screws during assembly.

4. Solder Resist/Solder Mask: Not all copper surfaces need to be tinned for component mounting. Therefore, in areas where soldering is not required, a layer of material that prevents the copper surface from being soldered—typically epoxy resin—is applied to isolate these areas and avoid short circuits between non-soldered traces. Depending on the specific process, these materials are categorized as green oil, red oil, or blue oil.

5. Silk-screen printing (Legend/Marking/Silk screen): This is a non-essential component whose primary function is to label the names and location frames of various components on the circuit board, facilitating maintenance and identification after assembly.

6. Surface Finish: Since copper surfaces tend to oxidize easily in normal environments, making it difficult to solder (resulting in poor solderability), protective treatments are applied to copper surfaces that require soldering. Common protection methods include Hot Air Solder Leveling (HASL), Electroless Nickel Immersion Gold (ENIG), Immersion Silver, Immersion Tin, and Organic Solderability Preservative (OSP). Each method has its own advantages and disadvantages; collectively, these are referred to as surface finishes.

III. Brief History of Development

Before the advent of printed circuit boards, interconnections between electronic components were established by directly wiring them together to form complete circuits. Today, circuit breadboards exist only as effective experimental tools, while printed circuit boards have firmly established themselves as the dominant technology in the electronics industry.

In the early 20th century, in order to simplify the manufacturing of electronic devices, reduce wiring between electronic components, and lower production costs, people began exploring ways to replace wiring with printing techniques. Over the course of three decades, engineers continually proposed using metallic conductors deposited onto insulating substrates as a means of wiring.

The most successful achievement was in 1925, when Charles Ducas of the United States printed circuit patterns onto an insulating substrate and then successfully created conductors for wiring through electroplating.

It wasn't until 1936 that the Austrian Paul Eisler published the foil-film technology in the United Kingdom, where he introduced printed circuit boards into a radio set. Meanwhile, in Japan, Yoshinosuke Miyamoto successfully obtained a patent for his spray-coating wiring method, known as the "Metallicon Spraying Wiring Method" (Patent No. 119384). Of these two approaches, Paul Eisler's method bore the greatest resemblance to today's printed circuit boards. This approach is called the subtractive method, in which unwanted metal is removed. In contrast, the methods developed by Charles Ducas and Yoshinosuke Miyamoto involved adding only the necessary wiring—thus earning them the name "additive method." Nevertheless, due to the high heat generation of electronic components at the time, both methods' substrates proved difficult to match effectively, preventing their widespread adoption. Nonetheless, these early efforts laid the groundwork for further advancements in printed circuit technology.

In 1941, the United States applied a copper paste coating to talc as a wiring material to produce proximity fuses.

In 1943, Americans began extensively using this technology in military radios.

In 1947, epoxy resin began to be used in the manufacture of printed circuit boards. At the same time, NBS started researching manufacturing techniques for components such as coils, capacitors, and resistors using printed circuit technology.

In 1948, the United States officially approved this invention for commercial use.

Starting in the 1950s, as lower-heat-generating transistors began to largely replace vacuum tubes, printed circuit board technology started to be widely adopted. At that time, etching foil film technology was the mainstream approach.

In 1950, Japan used silver paint for wiring on glass substrates and copper foil for wiring on phenolic resin-based paper phenolic substrates (CCL).

In 1951, the emergence of polyimide further enhanced the heat resistance of resins and led to the development of polyimide substrates.

In 1953, Motorola developed the double-sided printed circuit board using the plated-through-hole technique. This method was also later applied to multilayer circuit boards.

By the 1960s, ten years after printed circuit boards had become widely adopted, their technology had also grown increasingly mature. Since Motorola introduced the dual-panel board, multilayer printed circuit boards began to emerge, further enhancing the ratio of wiring to substrate area.

In 1960, V. Dahlgreen created flexible printed circuit boards by laminating metal foil films with circuits onto thermoplastic plastics. In 1961, the U.S. company Hazeltine Corporation, drawing on the through-hole plating method, developed multilayer printed circuit boards.

In 1967, the “Plated-up technology,” one of the multilayering methods, was published.

In 1969, FD-R manufactured flexible printed circuit boards using polyimide.

In 1979, Pactel published the “Pactel Method,” one of the incremental-layer methods.

In 1984, NTT developed the “Copper Polyimide Method” for thin-film circuits.

In 1988, Siemens developed the multilayer printed circuit board known as the Microwiring Substrate.

In 1990, IBM developed the multilayer printed circuit board known as the “Surface Laminar Circuit” (SLC).

In 1995, Panasonic developed the ALIVH multilayer printed circuit board.

In 1996, Toshiba developed a multilayer printed circuit board with bit-level stacking.

Just as numerous multilayer printed circuit board solutions were being proposed in the late 1990s, multilayer printed circuit boards were also officially and extensively put into practical use—and remain so to this day.