What is the appearance and composition of the printed circuit board?

Composition

The current circuit board is mainly composed of the following
Line and pattern (Pattern): The line is used as a tool for conduction between the originals. In the design, a large copper surface will be designed as a grounding and power supply layer. Lines and drawings are made at the same time.
Dielectric layer: used to maintain the insulation between lines and layers, commonly known as the substrate.
Through holes / vias: Through holes can make more than two layers of circuits conduct with each other, larger through holes are used as part plug-ins, and non-through holes (nPTH) are usually used as surface mounts For positioning, it is used for fixing screws during assembly.Solder resistant /Solder Mask: Not all copper surfaces need to eat tin parts, so the non-tin areas will be printed with a layer of material (usually epoxy resin) that isolates the copper surface from eating tin. Short circuit between lines that do not eat tin. According to different processes, it is divided into green oil, red oil and blue oil.
Silk screen (Legend/Marking/Silk screen): This is a non-essential component. The main function is to mark the name and position frame of each part on the circuit board, which is convenient for maintenance and identification after assembly.
Surface Finish: Since the copper surface is easily oxidized in the general environment, it cannot be tinned (poor solderability), so it will be protected on the copper surface that needs to eat tin. The protection methods include spray tin (HASL), chemical gold (ENIG), silver (Immersion Silver), tin (Immersion Tin), organic solder protection agent (OSP), each method has advantages and disadvantages, collectively referred to as surface treatment.

Exterior

A bare board (with no parts on it) is also often referred to as a “Printed Wiring Board (PWB)”. The base plate of the board itself is made of insulating material that is not easily bendable. The thin circuit material that can be seen on the surface is copper foil. Originally, the copper foil covered the entire board, but part of it was etched away during the manufacturing process, and the remaining part became a mesh-like thin circuit. . These lines are called conductor patterns or wiring, and are used to provide electrical connections to components on the PCB.
Usually the color of the PCB is green or brown, which is the color of the solder mask. It is an insulating protective layer, which can protect the copper wire, prevent short circuit caused by wave soldering, and save the amount of solder. A silk screen is also printed on the solder mask. Usually, text and symbols (mostly white) are printed on this to indicate the position of each part on the board. The screen printing side is also called the legend side.
In the final product, integrated circuits, transistors, diodes, passive components (such as resistors, capacitors, connectors, etc.) and various other electronic parts are mounted on it. Through the connection of wires, electronic signal connections and due functions can be formed.