Analysis of PCB copper clad laminate manufacturing

PCB copper clad laminate classification

The PCB copper clad laminate consists of copper foil, reinforcing material and adhesive. Substrate material are usually classified by reinforcement class and adhesive type or substrate properties.

1. Classification of reinforcing materials. The most commonly used reinforcing materials for PCB copper clad laminates are alkali-free (alkali metal oxide content not exceeding 0.5%) glass fiber products (such as glass cloth, glass felt) or paper (such as wood pulp paper, Bleached wood pulp paper, cotton paper, etc.). Therefore, PCB copper clad laminates can be divided into two categories: glass cloth and paper substrate.

2. According to the type of adhesive, the adhesives used for the PCB foil clad board are mainly include phenolic, epoxy, polyester, polyimide, and PTFE resin etc. Therefore, the PCB foil clad board is accordingly divided into phenolic type. Epoxy, polyester, polyimide, PTFE PCB foil.

3. According to the characteristics of the substrate and usage classification, according to the degree of combustion of the substrate in the flame and after leaving the fire source can be divided into general-purpose and self-extinguishing; according to the degree of bending of the substrate can be divided into rigid and flexible PCB foil-clad; According to the working temperature and working environment conditions of the substrate, it can be divided into heat-resistant type, anti-radiation type, high frequency PCB clad board etc. In addition, there are PCB foil boards used in special occasions, such as prefabricated inner layer cladding board, metal substrate foil clad boards, and copper foil, nickel foil, silver foil, aluminum foil, and constantan foil,beryllium copper foil according to the type of foil.

4. Commonly used PCB foil clad board models are in accordance with GB4721-1984 regulation. PCB copper clad laminates are generally represented by five English letter combinations: the first letter C indicates the covered copper foil, and the second and third letters indicate the adhesive resin chosen of substrate. For example: PE means phenolic; EP means epoxy; uP means unsaturated polyester; SI means organic silicone; TF means polytetrafluoroethylene; PI means polyimide. The fourth and fifth letters indicate the reinforcing material selected for the substrate. For example: CP means cellulose fiber paper; GC means alkali-free glass fiber cloth; GM means alkali-free glass fiber felt.

For example, if the inner core of the PCB foil clad board is made of fiber paper or cellulose, and the non-alkali glass cloth is attached to both sides,G can be added behind GP. The two digits to the right of the horizontal line indicate the product number of the same type and different performance. For example, copper clad phenolic paper laminates are numbered O1 to 20, copper clad epoxy paper laminates are numbered from 21 to 30, and copper clad epoxy glass cloth laminates are numbered from 31 to 40. If added F behind the product number indicates that the PCB foil is self-extinguishing.

PCB copper clad laminate manufacturing method

The manufacturing of PCB copper clad laminates mainly includes three steps: resin solution preparation, reinforcement dipping and compress forming.

1. The main raw material for the manufacturing of PCB copper clad laminates

copper plate are resin, paper, glass cloth and copper foil.

(1) Resins for resin PCB copper clad laminates include phenol, epoxy, polyester, polyimide etc. Among them, the amount of phenolic resin and epoxy resin are the largest.

Phenolic resins are a class of resins in which phenols and aldehydes are polycondensed in an acidic medium or an alkaline medium. Among them, the resin which is polycondensed in an alkaline medium with phenol and formaldehyde is the main raw material of the paper substrate PCB clad board. In the manufacturing of paper substrate PCB foil clad, in order to obtain a variety of excellent performance of the substrate material, it is often necessary to improve performance the phenolic resin, and strictly control the free phenol and volatile content of the resin to ensure that the substrate is not layered or bubbles under thermal shock condition.

Epoxy resin is the main raw material of glass cloth substrate PCB foil clad board, which has excellent bonding properties and electrical and physical properties. More commonly used are E-20, E-44, E-51 and self-extinguishing E-20, E-25. In order to improve the transparency of the PCB foil substrate,so that checking the pattern defects in the production of printed boards, the epoxy resin should be required to have a lighter color.

(2)  Commonly used impregnated paper include: cotton wool paper, wood pulp paper and bleached wood pulp paper. The cotton wool paper is made of short fiber cotton fiber, which is characterized by good permeability of the resin, and the punching property and electrical properties of the board are also good. Wood pulp paper is mainly made of wood fiber, which is generally lower in price than cotton wool paper, and has higher mechanical strength. The usage of bleached wood pulp paper can improve the appearance of the board.

In order to improve the performance of the substrate, the thickness deviation, weight, breaking strength and water absorption of the impregnated paper need to be guaranteed.

(3) Alkali-free glass cloth is a reinforcing material for glass cloth substrate PCB covered foil board. For special high-frequency applications, quartz glass cloth can be used.

The alkali content of alkali-free glass cloth (expressed as Na20), IEC standard does not exceed 1%, JIS standard R3413-1978 does not exceed 0.8%, the former Soviet Union TOCT5937-68 standard does not exceed 0.5%, China Ministry of Construction the standard JC-170-80 specifies no more than 0.5%.

In order to meet the needs of general-purpose, thin and multi-layer printed boards, the types of glass cloth used for foreign PCB clad boards have been serialized. The thickness ranges from 0.025 to 0.234 mm. The specially required glass cloth is post-treated by coupling. In order to improve the mechanical processing performance and reduce the cost of the epoxy glass cloth substrate PCB foil clad board, non-woven glass fiber (also known as glass felt) has been developed in recent years.

(4) The foil of the copper foil PCB foil can be made of various metal foils such as copper, nickel and aluminum. However, in terms of electrical conductivity, weldability, elongation, adhesion to the substrate, and price of the metal foil, copper foil is most suitable except special purposes.

(5) Copper foil can be divided into rolled copper foil and electrolytic copper foil. The rolled copper foil is mainly used in flexible printed circuits and other special applications. In the production of PCB cladding, a large number of applications are electrolytic copper foil. For the purity of copper, IEC-249-34 and China's standards are required to not be less than 99.8%.

At present, the thickness of copper foil for domestic printed boards is 35um and 50um copper foil is used as a transition product. In the manufacturing of high-precision hole metallization double-sided or multi-layer board, it is desirable to use copper foil thinner than 35um, such as 18um. , 9um and 5um. Some multi-layer inner layer PCB clad boards use thick copper foil, such as 70um. In order to improve the adhesion strength of copper foil to the substrate, copper oxide foil is usually used (ie, oxidized to make a layer of copper oxide or cuprous oxide is formed on the surface of the foil, which enhances the bonding strength between the copper foil and the substrate due to polarity, or roughens the copper foil (electrochemical method is used to form a rough layer on the surface of the copper foil, The surface area of the copper foil is increased, and the adhesion strength between the copper foil and the substrate is improved by the anchoring effect of the roughened layer on the substrate.

In order to avoid the copper oxide powder falling off and moving onto the substrate, the surface treatment of the copper foil is also continuously improved. For example, the TW type copper foil is plated with a thin layer of zinc on the roughened surface of the copper foil, and the surface of the copper foil is gray; the TC type copper foil is plated with a thin layer of copper-zinc alloy on the roughened surface of the copper foil. This time the surface of the copper foil is gold. After special treatment, the anti-thermal discoloration , anti-oxidation of the copper foil and the anti-cyanide in the manufacturing of printed circuit boards are correspondingly improved.

The surface of the copper foil should be smooth and free of obvious wrinkles, oxidized spots, scratches, pitting, pits and smudging. The porosity rate of the copper foil of 305 g/m2 and above requires no more than 8 penetration points in the area of 300 ram × 300 mm; the total pore area of the copper foil on the area of 0.5 m2 does not exceed the circular area of 0.125 mm in diameter. The porosity rate and pore size of the copper foil below 305 g/m2 are determined by both the supplier and the buyer.

Before the copper foil is put into usage, it is sampled for compression test if necessary. The compression test can show its peel strength and general surface quality.

2. PCB copper clad laminate manufacturing technics

PCB copper foil laminate production technics process is as follows: resin synthesis and glue preparation - reinforcement material dipping and drying - dip material shear and inspection - dipping and copper foil lamination - hot press forming - cutting - inspection package.

The synthesis and formulation of the resin solution were carried out in a reaction vessel. Most of the phenolic resins used in paper substrate PCB clad laminates are synthesized by PCB clad laminates.

The glass cloth substrate PCB clad board is produced by mixing the epoxy resin and the curing agent provided by the raw material factory in acetone or dimethylformamide or ethylene glycol methyl ether, and stirring to make a uniform resin solution. The resin solution can be used for dipping after being aged for 8 to 24 hours.

Dipping is carried out on a dipping machine. The dipping machine is divided into horizontal and vertical. Horizontal dipping is mainly used for impregnating paper, and vertical dipping machine is mainly used for dipping high strength glass cloth. The paper or glass cloth impregnated with the resin liquid is cut into a certain size after being squeezed into the drying tunnel by the rubberizing roller, and is used after being inspected and qualified.