1. Introduction

PCB circuit board (printed circuit board), also known as printed circuit board, abbreviated as printed board, in English abbreviated as PCB (printed circuit board) or PWB (printed wiring board), is made of insulating board as the substrate, cut to a certain size, with at least one conductive pattern attached, and has holes (such as component holes, fastening holes, metallized holes, etc.) to replace the chassis for mounting electronic components and achieve mutual connection between electronic components. Since this board is made using electronic printing technology, it is called a "printed circuit board." It is inaccurate to habitually refer to "printed circuit board" as "printed circuit" because there are no "printed components" on the printed board, only wiring.

2. Basic Composition

The current circuit board mainly consists of the following components:

1. Lines and Patterns: The lines serve as a tool for conducting between components, and a large copper area is designed separately for grounding and power layers. The lines and patterns are made simultaneously.

2. Dielectric: Used to maintain insulation between lines and layers, also known as substrate.

3. Through hole / via: Conductive holes allow lines on two or more layers to connect with each other, while larger conductive holes are used for component insertion. Additionally, non-conductive holes (nPTH) are usually used for surface mount positioning and to secure screws during assembly.

4. Solder resistant / Solder Mask: Not all copper surfaces need to be soldered with components, so areas that do not require soldering will be printed with a layer of material (usually epoxy resin) to prevent soldering in non-solder areas, avoiding short circuits between non-soldered lines. Depending on different processes, it is divided into green oil, red oil, and blue oil.

5. Legend / Marking / Silk screen: This is a non-essential component, mainly used to label the names and position frames of various components on the circuit board for easier maintenance and identification after assembly.

6. Surface Finish: Since copper surfaces can easily oxidize in general environments, leading to poor solderability, protective measures are taken on copper surfaces that need soldering. The protection methods include Hot Air Solder Leveling (HASL), Electroless Nickel Immersion Gold (ENIG), Immersion Silver, Immersion Tin, and Organic Solderability Preservative (OSP), each with its advantages and disadvantages, collectively referred to as surface treatment.

3. Development History

Before the advent of printed circuit boards, the interconnection between electronic components was entirely dependent on direct wiring to form complete circuits. Now, circuit breadboards exist only as effective experimental tools, while printed circuit boards have become dominant in the electronics industry.

In the early 20th century, to simplify the production of electronic machines, reduce wiring between electronic components, and lower production costs, research began on methods to replace wiring with printing. Over thirty years, engineers continuously proposed adding metal conductors to insulated substrates for wiring.

The most successful was in 1925, when Charles Ducas from the United States printed circuit patterns on an insulated substrate and successfully established conductors for wiring through electroplating.

It wasn't until 1936 that Austrian Paul Eisler published foil technology in the UK, where he used printed circuit boards in a radio device; in Japan, Yoshinosuke Miyamoto successfully patented the "Metarikon method" for spray-applied wiring (Patent No. 119384). Among the two, Paul Eisler's method is most similar to today's printed circuit boards, known as the subtractive method, which removes unnecessary metal; while Charles Ducas and Yoshinosuke Miyamoto's methods only add the required wiring, known as the additive method. However, due to the high heat generation of electronic components at that time, the substrates of both methods were difficult to use together, resulting in no formal application, but it did advance printed circuit technology.

In 1941, the United States used copper paste on talc for wiring to produce proximity tube.

In 1943, Americans extensively used this technology in military radios.

In 1947, epoxy resin began to be used for manufacturing substrates. At the same time, NBS began researching the manufacturing technology of coils, capacitors, resistors, etc., using printed circuit technology.

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

From the 1950s onwards, low-heat-generating transistors largely replaced vacuum tubes, and printed circuit board technology began to be widely adopted. At that time, etching foil technology was the mainstream.

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

In 1951, the emergence of polyimide further improved the heat resistance of resin and led to the manufacture of polyimide substrates.

In 1953, Motorola developed the electroplated through-hole method for double-sided boards. This method was also applied to later multilayer circuit boards.

Printed circuit boards were widely used in the 1960s, ten years later, and their technology became increasingly mature. Since the introduction of Motorola's double-sided board, multilayer printed circuit boards began to appear, further increasing the ratio of wiring to substrate area.

In 1960, V. Dahlgreen created flexible printed circuit boards by attaching metal foil with printed circuits to thermoplastic plastics. In 1961, Hazeltine Corporation in the United States referenced the electroplated through-hole method to produce multilayer boards.

In 1967, one of the layering methods, "Plated-up technology," was published.

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

In 1979, Pactel published one of the layering methods, the "Pactel method."

In 1984, NTT developed the "Copper Polyimide method" for thin film circuits.

In 1988, Siemens developed the layered printed circuit board of Microwiring Substrate.

In 1990, IBM developed the layered printed circuit board of Surface Laminar Circuit (SLC).

In 1995, Panasonic developed the layered printed circuit board of ALIVH.

In 1996, Toshiba developed the layered printed circuit board of Bit.

In the late 1990s, when many multilayer printed circuit board solutions were proposed, multilayer printed circuit boards were officially put into practical use in large quantities, and this continues to this day.