PCB Technical - Discern the difference of PCB board material

The combustibility of a material, also known as flame retardancy, self-extinguishing, flame resistance, flame resistance, fire resistance, flammability and other combustibility, is to assess the ability of the material to resist combustion.

The flammable material sample is ignited with a flame that meets the requirements, and the flame is removed after the specified time. The flammability level is evaluated according to the degree of combustion of the sample. There are three levels. The horizontal test method of the sample is divided into FH1, FH2, FH3 level three, the vertical test method is divided into FV0, FV1, VF2.

The solid PCB board is divided into HB board and V0 board.

HB sheet has low flame retardancy and is mostly used for single-sided boards.

VO board has high flame retardancy and is mostly used in double-sided and multi-layer boards

This type of PCB board that meets the V-1 fire rating requirements becomes FR-4 board.

V-0, V-1, and V-2 are fireproof grades.

The circuit board must be flame-resistant, cannot burn at a certain temperature, but can only be softened. The temperature at this time is called the glass transition temperature (T), and this value is related to the dimensional stability of the PCB board.

What is a high Tg PCB circuit board and the advantages of using a high Tg PCB?

When the temperature of a high Tg printed board rises to a certain area, the substrate will change from "glass state" to "rubber state". The temperature at this time is called the glass transition temperature (Tg) of the board. In other words, Tg is the temperature at which the substrate maintains rigidity.

What are the specific types of PCB boards?

Divided by grade level from bottom to high as follows:

94HB － 94VO － 22F － CEM-1 － CEM-3 － FR-4

The details are as follows:

94HB: Ordinary cardboard, not fireproof (the material of the file is punched by the die, and it cannot be used as a power supply board)

94V0: Flame Retardant Cardboard (Die Punching)

22F: Single-sided half glass fiber board (die punching)

CEM-1: Single-sided fiberglass board (computer drilling is necessary, not die punching)

CEM-3: Double-sided semi-glass fiber board (except for double-sided cardboard, it is a material for the double-sided end. Simple double-sided board can use this material, which is 5~10 yuan/square meter cheaper than FR-4)

FR-4: Double-sided fiberglass board

The circuit board must be flame-resistant, cannot burn at a certain temperature, but can only be softened. The temperature at this time is called the glass transition temperature (T), and this value is related to the dimensional stability of the PCB board.

What is a high Tg PCB circuit board and the advantages of using a high Tg PCB. When the temperature rises to a certain area, the substrate will change from the "glass state" to the "rubber state".

The temperature at that time is called the glass transition temperature (Tg) of the plate. That is, Tg is the temperature (°C) at which the base material maintains rigidity. That is to say, ordinary PCB substrate materials not only produce softening, deformation, melting and other phenomena at high temperatures, but also show a sharp decline in mechanical and electrical characteristics (I think you don’t want to see the classification of PCB boards and see this situation in your own products. ).

The general Tg plate is more than 130 degrees, the high Tg is generally more than 170 degrees, and the medium Tg is about more than 150 degrees.

Usually PCB printed boards with Tg ≥ 170°C are called high Tg printed boards.

As the Tg of the substrate increases, the heat resistance, moisture resistance, chemical resistance, stability and other characteristics of the printed board will be improved and improved. The higher the TG value, the better the temperature resistance of the board, especially in the lead-free process, where high Tg applications are more common.

High Tg refers to high heat resistance. With the rapid development of the electronics industry, especially computer-based electronic products, the development of high-functionality and high-multilayer development requires the higher heat resistance of PCB substrate materials as an important guarantee. The emergence and development of high-density mounting technologies based on SMT and CMT have made PCBs more and more inseparable from the support of high heat resistance of substrates in terms of small aperture, fine circuit and thinner.

Therefore, the difference between general FR-4 and high-Tg FR-4 is the mechanical strength, dimensional stability, adhesion, water absorption, and thermal decomposition of the material in the hot state, especially when heated after moisture absorption. There are differences in various conditions, such as thermal expansion, and high Tg products are obviously better than ordinary PCB substrate materials.

In recent years, the number of customers requiring the production of high Tg printed boards has increased year by year.

With the development and continuous progress of electronic technology, new requirements are constantly being put forward for printed circuit board substrate materials, thereby promoting the continuous development of copper clad laminate standards. At present, the main standards of substrate materials are as follows.

1. National Standards At present, China's national standards for the classification of substrate materials PCB boards are GB/T4721-47221992 and GB4723-4725-1992. The copper clad laminate standard in Taiwan, China is the CNS standard, which is based on the Japanese JIs standard., Released in 1983.

2. Other national standards include: Japanese JIS standards, American ASTM, NEMA, MIL, IPc, ANSI, UL standards, British Bs standards, German DIN and VDE standards, French NFC and UTE standards, and Canadian CSA Standards, AS standards in Australia, FOCT standards in the former Soviet Union, international IEC standards, etc.

The suppliers of the original PCB design materials are common and commonly used: Shengyi \ Jiantao \ International, etc.

. Accept documents: protel autocad powerpcb orcad gerber or real board copy board, etc.

. Sheet types: CEM-1, CEM-3 FR4, high TG materials;

. Board size: 600mm*700mm (24000mil*27500mil)

. Processing board thickness: 0.4mm-4.0mm (15.75mil-157.5mil)

. Number of processing layers: 16Layers

. Copper foil layer thickness: 0.5-4.0(oz)

. Finished board thickness tolerance: +/-0.1mm(4mil)

. Forming size tolerance: computer milling: 0.15mm (6mil) die punching plate: 0.10mm (4mil)

. Small line width/spacing: 0.1mm (4mil) Line width control ability: <+-20%

. Finished small hole diameter: 0.25mm (10mil)

Finished small punch hole diameter: 0.9mm (35mil)

Finished hole tolerance: PTH: +-0.075mm(3mil)

NPTH: +-0.05mm(2mil)

. Finished hole wall copper thickness: 18-25um (0.71-0.99mil)

. Small SMT patch spacing: 0.15mm (6mil)

. Surface coating: chemical immersion gold, tin spray, nickel-plated gold (water/soft gold), silk screen blue glue, etc.

. The thickness of the solder mask on the board: 10-30μm (0.4-1.2mil)

. Peeling strength: 1.5N/mm (59N/mil)

. Hardness of solder mask: >5H

. Solder mask plug hole capacity: 0.3-0.8mm (12mil-30mil)

. Dielectric constant: ε= 2.1-10.0

. Insulation resistance: 10KΩ-20MΩ

. Characteristic impedance: 60 ohm±10%

. Thermal shock: 288 degree Celsius, 10 sec

. Warpage of finished board: <0.7%

. Product application: communication equipment, automotive electronics, instrumentation, global positioning system, computer, MP4, power supply, home appliances, etc.

According to PCB board reinforcement materials, it is generally divided into the following types:

1. Phenolic PCB paper substrate

Because this kind of PCB board is composed of paper pulp, wood pulp, etc., it sometimes becomes cardboard, V0 board, flame-retardant board and 94HB, etc. Its main material is wood pulp fiber paper, which is a kind of PCB synthesized by phenolic resin pressure. plate.

This kind of paper substrate is not fireproof, can be punched, has low cost, low price, and low relative density. We often see phenolic paper substrates such as XPC, FR-1, FR-2, FE-3, etc. And 94V0 belongs to flame-retardant paperboard, which is fireproof.

2. Composite PCB substrate

This kind of powder board is also called powder board, with wood pulp fiber paper or cotton pulp fiber paper as reinforcement material, and glass fiber cloth as surface reinforcement material at the same time. The two materials are made of flame-retardant epoxy resin. There are single-sided half-glass fiber 22F, CEM-1 and double-sided half-glass fiber board CEM-3, among which CEM-1 and CEM-3 are currently common composite base copper clad laminates.

3. Glass fiber PCB substrate

Sometimes it also becomes epoxy board, glass fiber board, FR4, fiber board, etc. It uses epoxy resin as adhesive and glass fiber cloth as reinforcement material. This kind of circuit board has a high working temperature and is not affected by the environment. This kind of board is often used in double-sided PCB, but the price is more expensive than the composite PCB substrate, and the common thickness is 1.6MM. This kind of substrate is suitable for various power supply boards, high-level circuit boards, and is widely used in computers and equipment, communication equipment, etc.

FR-4

4. Other substrates

In addition to the three frequently seen above, there are also metal substrates and build-up multi-layer boards (BUM).