How Much Do You Know About PCB Classification?!

PCBs come in a wide variety of materials, layer counts, and manufacturing processes to accommodate different electronic products and their specific requirements, resulting in numerous classifications.

Below, we summarize some common classification methods to briefly introduce PCB types and their manufacturing processes.

Let’s analyze this from three perspectives.

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. 

When sold on the market, it is often mixed with colorants to produce red, yellow, black, green, brown, blue, and other colors, and is available in granular or powdered forms.

Phenolic resin is resistant to weak acids and weak alkalis; it decomposes when exposed to strong acids and corrodes when exposed to strong alkalis. 

It is insoluble in water but soluble in organic solvents such as acetone and alcohol. It is obtained through the polycondensation of phenol and formaldehyde or their derivatives. See the image below:

② Glass Fiber:

Glass fiber (original English name: glass fiber) is an inorganic non-metallic material with excellent properties. It comes in a wide variety of types and offers advantages such as good insulation, high heat resistance, strong corrosion resistance, and high mechanical strength. 

However, its disadvantages include brittleness and relatively poor wear resistance.

It is manufactured through processes such as high-temperature melting, filament drawing, yarn winding, and weaving, using seven types of raw materials: micaceous schist, quartz sand, limestone, dolomite, calcium borate, and magnesium borate. 

The diameter of a single filament ranges from a few micrometers to over twenty micrometers, equivalent to 1/20 to 1/5 the thickness of a human hair. Each bundle of fiber roving consists of hundreds or even thousands of individual filaments.

Glass fiber is commonly used as a reinforcing material in composites, as an electrical insulator and thermal insulation material, and in circuit boards across various sectors of the national economy. See image below:

③ Polyimide:

Polyimide resin, abbreviated as PI, appears as a transparent liquid, yellow powder, brown granules, or amber granules. 

It is available in liquid, solution, powder, granule, and pellet forms. polyimide resin pellets, 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, cast film, lamination, foaming, transfer molding, and compression molding.

Our epoxy resins and BT resins, among others, also belong to the category of organic materials.

2. Inorganic Materials:

① Aluminum Substrates: Aluminum substrates are metal-based copper-clad laminates with excellent heat dissipation properties. Single-sided boards typically consist of a three-layer structure.

These layers are the circuit layer (copper foil), the insulating layer, and the metal base layer. They are commonly used in LED lighting products.

There are two sides: the white side is used for soldering LED leads, while the other side retains the natural aluminum color and is typically coated with thermal paste before contacting the heat-dissipating component. Currently, ceramic substrates and others are also available.

② Copper Substrates: Copper substrates are the most expensive type of metal substrate. Their thermal conductivity is many times better than that of aluminum and iron substrates. 

They are suitable for high-frequency circuits, regions with significant temperature fluctuations, heat dissipation in precision communication equipment, and the architectural decoration industry.

Ceramic substrates and others also fall under inorganic materials, primarily valued for their heat dissipation capabilities.

II. Rigidity of Finished Products

1. Rigid Sheets:

Rigid sheets are panels made from PVC. PVC rigid sheets are widely used in industry, particularly in the chemical and corrosion-resistant sectors.

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

2. Flexible Sheets:

Soft PVC extruded sheets are produced by extruding a mixture of PVC resin, plasticizers, stabilizers, and other additives.

They are primarily used as linings for corrosion-resistant equipment requiring acid and alkali resistance. They can also serve as general electrical insulation and sealing gasket materials. 

With an operating temperature range of -5 to +40°C, they can be used as a substitute for rubber sheets and are widely applicable as a new type of environmentally friendly product.

3. Rigid-Flex Boards:

The emergence and development of FPCs and PCBs have given rise to a new product: rigid-flex boards. 

herefore, rigid-flex boards are circuit boards formed by combining flexible printed circuits (FPCs) and printed circuit boards (PCBs) through processes such as lamination, in accordance with relevant technical requirements, resulting in a board that possesses the characteristics of both FPCs and PCBs.

III. Structure

1. Single-sided PCB:

A single-sided PCB is the most basic type of PCB, where components are mounted on one side and conductive traces are routed on the other.

Since the conductive traces appear on only one side, this type of PCB is referred to as a single-sided PCB.

Because single-sided PCBs have many strict design constraints (since there is only one side, traces cannot cross and must follow separate paths), they were primarily used in early circuit designs.

2. Double-Sided PCB:

A double-sided PCB is a printed circuit board with copper layers on both the top (Top) and bottom (Bottom) surfaces. 

Both sides can be routed and soldered, with an insulating layer in between; it is a commonly used type of printed circuit board.

Since routing can be performed on both sides, the difficulty of routing is greatly reduced, making this type widely adopted.

3. Multilayer Boards:

Multilayer boards are typically manufactured by first creating the inner layer patterns, then using the printed etching method to produce single- or double-sided substrates, which are inserted into the designated interlayers. 

These are then heated, pressed, and bonded together. The subsequent drilling process is the same as the plated-through-hole method used for double-sided boards.

The above outlines the classification of PCBs from three perspectives.