How much do you know about the classification of PCB?

PCBs (Printed Circuit Boards) vary in materials, number of layers, and manufacturing processes to suit different electronic products and their specific needs, resulting in numerous classifications.

 

Below are some common methods of differentiation to briefly introduce the classification of PCBs and their manufacturing processes. Let's analyze them from three aspects:

 

I. Materials

 

1. Organic Materials:

 

① Phenolic Resin: Phenolic resin, also known as Bakelite or Bakelite powder, is originally a colorless or yellowish-brown transparent substance. In the market, it is often colored with colorants to appear red, yellow, black, green, brown, blue, etc., and exists in granular or powder form.

Phenolic resin is resistant to weak acids and weak alkalis, but decomposes in strong acids and corrodes in strong alkalis. It is insoluble in water but soluble in organic solvents such as acetone and alcohol. It is obtained by the condensation polymerization of phenolic resin or its derivatives.

② Glass fiber: Glass fiber is a high-performance inorganic non-metallic material with many varieties. Its advantages include good insulation, strong heat resistance, good corrosion resistance, and high mechanical strength. However, its disadvantages include brittleness and poor wear resistance.

It is made from seven minerals-pyrophyllite, quartz sand, limestone, dolomite, borosilicate, and boromagnesia-through high-temperature melting, drawing, winding, and weaving processes. The diameter of its single filaments ranges from a few micrometers to over twenty micrometers, equivalent to 1/20 to 1/5 the diameter of a human hair. Each bundle of fiber consists of hundreds or even thousands of single filaments.

Glass fiber is commonly used as a reinforcing material in composite materials, an electrical insulation material, a thermal insulation material, and in circuit boards, among other applications across various sectors of the national economy.

③ Polyimide: Polyimide resin, abbreviated as PI, appearance: transparent liquid, yellow powder, brown granules, amber granules. Polyimide resin liquid, polyimide resin solution, polyimide resin powder, polyimide resin granules, polyimide resin pellets, polyimide resin granules, thermoplastic polyimide resin solution, thermoplastic polyimide resin powder, thermosetting polyimide resin solution, thermosetting polyimide resin powder, thermoplastic pure polyimide resin, thermosetting pure polyimide resin. II. Polyimide (PI) molding methods include: high-temperature curing, compression molding, impregnation, spraying, calendering, injection molding, extrusion, die casting, coating, casting, lamination, foaming, transfer molding, and compression molding.

 

Also, our epoxy resin and BT, etc., are all organic materials.

 

2. Inorganic Materials:

 

① Aluminum Substrate: An aluminum substrate is a copper-clad laminate with excellent heat dissipation properties. A typical single-sided board consists of three layers:

the circuit layer (copper foil), the insulating layer, and the metal base layer. Commonly found in LED lighting products. It has two sides; the white side is for soldering LED leads, and the other side is the natural aluminum color, usually coated with thermally conductive paste before contact with the heat-conducting parts. Ceramic substrates are also available. (See figure).

② Copper Substrate: Copper substrates are the most expensive type of metal substrate. Their thermal conductivity is many times better than aluminum and iron substrates, making them suitable for high-frequency circuits, areas with large temperature variations, heat dissipation in precision communication equipment, and the building decoration industry. (See figure).

 

Ceramic substrates and others are also inorganic materials, primarily used for their heat dissipation function.

 

II. Finished Product Rigidity

 

1. Rigid Board: A rigid board is a sheet material made from PVC. PVC rigid boards are widely used in industry, especially in the chemical corrosion protection industry.

PVC is a resin resistant to acids, alkalis, and salts. Due to its excellent chemical properties and relatively low price, it is widely used in various industries such as chemical, building materials, light industry, and machinery.

2. Flexible Circuit Board: Flexible PVC extruded sheets are made by extruding PVC resin with plasticizers, stabilizers, etc.

It is mainly used for lining acid- and alkali-resistant corrosion-resistant equipment. It can also be used as a general electrical insulation and sealing gasket material. Its operating temperature is -5 to +40℃. It can be used as a substitute for rubber sheets and is a widely applicable, new type of environmentally friendly product. (See figure)

3. Rigid-Flex Board: The birth and development of FPC and PCB gave rise to the new product, the rigid-flex board. Therefore, a rigid-flex board is a circuit board that combines flexible and rigid circuit boards through processes such as lamination, according to relevant process requirements, forming a circuit board with both FPC and PCB characteristics. (See figure)

 

III. Structure

 

1. Single-sided Board: A single-sided board is based on the most basic PCB, where components are concentrated on one side and conductors are concentrated on the other. Because the traces only appear on one side, this type of PCB is called a single-sided PCB.

Single-sided PCBs have many strict limitations in circuit design (because there's only one side, traces cannot cross and must follow their own paths), so only early circuits used this type of board. See figure:

2. Double-sided PCB: A double-sided PCB is a printed circuit board with copper plating on both sides, including the top and bottom layers. Traces can be soldered on both sides, with an insulating layer in between. It is a commonly used type of printed circuit board.

The ability to route traces on both sides greatly reduces the difficulty of routing, hence its widespread adoption. See figure:

3. Multilayer PCB: The manufacturing method of multilayer PCBs generally involves first creating the inner layer pattern, then using printing and etching to create a single-sided or double-sided substrate, which is then placed into the designated layers. It is then heated, pressurized, and bonded. The subsequent drilling is the same as the plated through-hole method for double-sided PCBs. See figure:

The above are three classifications of PCB.