PCB Blog - Manufacturing method of copper clad laminate for PCB board

PCB board copper clad laminate is a substrate material for making printed circuit boards. In addition to supporting various components, it can realize electrical connection or electrical insulation between them. The manufacturing process of PCB board foil-clad board is to impregnate glass fiber cloth, glass fiber mat, paper and other reinforcing materials with epoxy resin, phenolic resin and other adhesives, and dry it at an appropriate temperature to stage B to obtain pre-impregnated materials ( Abbreviated as dipping material), and then laminate them with copper foil according to the process requirements, and heat and pressurize them on the laminator to obtain the required PCB board copper-clad laminate.

1. Classification of PCB board copper clad laminate PCB board copper clad laminates are composed of three parts: copper foil, reinforcing materials and adhesives. Sheets are generally classified by reinforcement class and adhesive class or by sheet properties.
1. Classification by reinforcing materials The commonly used reinforcing materials for PCB board copper-clad laminates are alkali-free (alkali metal oxide content not exceeding 0.5%) glass fiber products (such as glass cloth, glass mat) or paper (such as wood pulp paper, bleached wood pulp paper, lint paper), etc. Therefore, PCB board copper clad laminates can be divided into two categories: glass cloth base and paper base.
2. According to the type of adhesive, the adhesives used in PCB foil-clad laminates are mainly phenolic, epoxy, polyester, polyimide, PTFE resin, etc. Therefore, PCB foil-clad laminates are also divided into phenolic resins accordingly. Type, epoxy type, polyester type, polyimide type, PTFE type PCB board foil clad board.
3. According to the characteristics and uses of the base material, it can be divided into general-purpose type and self-extinguishing type according to the burning degree of the base material in the flame and after leaving the fire source; according to the bending degree of the base material, it can be divided into rigid and flexible PCB board foil-clad board ; 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 board foil-clad board, etc. In addition, there are also PCB board foil clad laminates used in special occasions, such as prefabricated inner layer foil clad laminates, metal-based foil clad laminates, and can be divided into copper foil, nickel foil, silver foil, aluminum foil, constantan foil according to the type of foil., Beryllium copper foil clad laminate.
4. Commonly used PCB board foil-clad laminate models are specified in GB4721-1984. PCB board copper-clad laminates are generally represented by a combination of five English letters: the letter C represents the clad copper foil, and the second and third letters represent the base material. Selected binder resin. For example: PE means phenolic; EP means epoxy; uP means unsaturated polyester; SI means silicone; TF means polytetrafluoroethylene; PI means polyimide. The fourth and fifth letters indicate the reinforcing material selected for the base material. For example: CP means cellulose fiber paper; GC means alkali-free glass fiber cloth; GM means alkali-free glass fiber mat. For example, if the inner core of the base material of the PCB board foil-clad board is reinforced with fiber paper and cellulose, and the alkali-free glass cloth is attached to both sides, the two digits to the right of the horizontal line in the model number can be added after CP, indicating the same type And different performance product number. For example, the number of copper clad phenolic paper laminate is O1~20, the number of copper clad epoxy paper laminate is 21~30; the number of copper clad epoxy glass cloth laminate is 31~40. The letter F means that the PCB board foil-clad board is self-extinguishing.

2. Manufacturing method of copper clad laminate for PCB board The manufacture of copper clad laminate for PCB board mainly includes three steps of resin solution preparation, dipping of reinforcing material and compression molding.
1. The main raw materials for the manufacture of copper clad laminates for PCB boards The main raw materials for the manufacture of copper clad laminates are resin, paper, glass cloth, and copper foil.
(1) The resins used for the copper-clad laminates of the resin PCBs include phenolic, epoxy, polyester, polyimide, etc. Among them, the amount of phenolic resin and epoxy resin is used. Phenolic resin is a type of resin formed by polycondensation of phenols and aldehydes in acidic or alkaline media. Among them, the resin polycondensed with phenol and formaldehyde in an alkaline medium is the main raw material of paper-based PCB board foil-clad board. In the manufacture of paper-based PCB board foil-clad board, in order to obtain various boards with excellent performance, it is often necessary to modify phenolic resins in various ways, and strictly control the free phenol and volatile content of the resin to ensure that the board is under thermal shock. No delamination, no foaming. Epoxy resin is the main raw material of glass cloth-based PCB board foil-clad board, which has excellent bonding properties and electrical and physical properties. The more commonly used types are E-20, E-44, E-51 and self-extinguishing E-20 and E-25. In order to improve the transparency of the substrate of the PCB board foil cladding board, so as to check the pattern defects in the production of the printed board, it is required that the epoxy resin should have a lighter color.
(2) Impregnated paper commonly used impregnated paper includes cotton lint paper, wood pulp paper and bleached wood pulp paper. Cotton lint paper is made of cotton fibers with shorter fibers, which is characterized by better resin permeability, and better punching and electrical properties of the board. Wood pulp paper is mainly made of wood fiber, which is generally lower in price than cotton lint paper, and has higher mechanical strength. The use of bleached wood pulp paper can improve the appearance of the board. In order to improve the performance of the board, the thickness deviation, weight, breaking strength and water absorption of the impregnated paper need to be guaranteed.
(3) Alkali-free glass cloth Alkali-free glass cloth is a reinforcing material for glass cloth-based PCB board foil-clad board. For special high-frequency applications, quartz glass cloth can be used. For the alkali content of alkali-free glass cloth (expressed as Na20), the IEC standard stipulates that it does not exceed 1%, the JIS standard R3413-1978 stipulates that it does not exceed 0.8%, and the former Soviet Union TOCT5937-68 standard stipulates that it does not exceed 0.5%. The Ministry of Construction of my country Standard JC-170-80 stipulates not more than 0.5%. In order to meet the needs of general-purpose, thin and multi-layer printed boards, the glass cloth models for foreign PCB board foil-clad boards have been serialized. Its thickness ranges from 0.025 to 0.234 mm. Specially required glass cloths are post-treated by coupling. In order to improve the machining performance of epoxy glass cloth-based PCB board foil-clad board and reduce the cost of the board, non-woven glass fiber (also known as glass mat) has been developed in recent years.
(4) The foil of copper foil PCB board foil clad board can be made of copper, nickel, aluminum and other metal foils. However, considering the conductivity, solderability, elongation, adhesion to the substrate and price of the metal foil, copper foil is suitable except for special purposes. Copper foil can be divided into rolled copper foil and electrolytic copper foil. Rolled copper foil is mainly used in flexible printed circuits and other special purposes. Electrolytic copper foil is widely used in the production of foil-clad PCBs. For the purity of copper, IEC-249-34 and Chinese standards both stipulate that it should not be lower than 99.8%. At present, the copper foil thickness of domestic printed boards is mostly 35um, and 50um copper foil is used as a transition product. In the manufacture of high-precision hole metallized double-sided or multi-layer boards, it is hoped to use copper foil thinner than 35um, such as 18um, 9um and 5um. Some multi-layer boards use thicker copper foils, such as 70um. A layer of copper oxide or cuprous oxide is formed on the surface of the copper foil, which improves the bonding strength between the copper foil and the substrate due to the effect of polarity) or roughened copper foil (a roughening layer is formed on the surface of the copper foil by electrochemical methods., increasing the surface area of the copper foil, and improving the bonding strength of the copper foil and the substrate due to the anchoring effect of the roughened layer on the substrate). In order to avoid the copper oxide powder falling off and moving to the substrate, the surface treatment method of 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 at this time; the TC type copper foil is plated with a thin layer of copper-zinc alloy on the roughened surface of the copper foil. When the copper foil surface is gold. After special treatment, the thermal discoloration resistance, oxidation resistance and cyanide resistance of copper foil in the manufacture of printed circuit boards are improved accordingly. The surface of the copper foil should be smooth and free of obvious wrinkles, oxidation spots, scratches, pits, pits and stains. The porosity of copper foil of 305g/m2 and above requires no more than 8 penetration points in an area of 300ram * 300mm; the total pore area of copper foil in an area of 0.5m2 does not exceed the area of a circle with a diameter of 0.125mm. The porosity and hole size of copper foil below 305g/m2 shall be negotiated by both parties. Before the copper foil is put into use, if necessary, take samples for pressing test. Compression tests show its peel strength and general surface quality.

2. Manufacturing process of copper clad laminate Copper foil lamination - thermoforming - cutting - inspection packaging. The synthesis and preparation of the resin solution are all carried out in the reactor. Most of the phenolic resins used in paper-based PCB foil-clad laminates are synthesized by PCB foil-clad laminate factories. The production of glass cloth-based PCB board foil-clad board is to mix and dissolve the epoxy resin and curing agent provided by the raw material factory in acetone or dimethylformamide, ethylene glycol methyl ether, and stir to make it into a uniform resin solution. The resin solution can be used for dipping after curing for 8 to 24 hours. Dipping is carried out on a dipping machine. There are two types of dipping machines: horizontal and vertical. The horizontal dipping machine is mainly used for impregnating paper, and the vertical dipping machine is mainly used for dipping glass cloth with high strength. The paper or glass cloth impregnated with resin liquid is mainly cut into a certain size after being dried in the drying tunnel by the extrusion roller, and is ready for use after passing the inspection on PCB board.