Electronic Design - PCB technology Waste circuit board processing and reuse technology

PCB technology Waste circuit board processing and reuse technology

The recycling of waste circuit boards is an emerging industry. With the scrapping of a large number of household appliances, the number of waste circuit boards is increasing, and its recycling value has also attracted the attention of many investors and has become a promising industry. The composition of waste circuit boards is complex and the recycling process is difficult. In addition, a large amount of organic substances are added to the circuit boards during the production process. Any carelessness in the recycling process of waste circuit boards may cause serious pollution to the environment. At present, my country's waste circuit board recycling technology is still relatively backward, and the development of advanced waste circuit board processing technology has become the object of research by many technicians. This article intends to introduce and comment on the current recycling technology of waste circuit boards.

1. The composition of waste circuit boards
Waste circuit boards include waste copper clad laminates (CCL), waste printed circuit boards(PCB), printed circuit boards with integrated circuits and electronic devices (generally called waste circuit boards).

1. Waste copper clad laminate

Copper clad laminate is the raw material for the production of printed circuit boards, mainly composed of substrates, copper foils, and adhesives. The main materials of the substrate are synthetic resins and reinforcing materials. Among them, synthetic resins mainly include phenolic resin, epoxy resin, polytetrafluoroethylene, etc., and reinforcing materials generally include paper and cloth.

The surface of the substrate is copper foil. The copper foil is produced by mechanical processing and electrowinning. At present, it is mainly produced by electrowinning. The thickness of copper foil is generally 18μm, 25μm, 35μm, 70μm, and 105μm. The copper foil is firmly adhered to the substrate with an adhesive to form a copper clad laminate.

At present, a large number of copper clad laminates used in my country include phenolic paper copper clad laminates, epoxy paper copper clad laminates, epoxy glass cloth copper clad laminates, polytetrafluoroethylene copper clad laminates, and polyimide flexible copper clad laminates. Among them, mid-range and above civilian electrical appliances, The instruments and meters use epoxy (paper or glass cloth) copper clad laminates, and the amount is relatively large. Phenolic paper copper clad laminates are mostly used in low- and medium-grade civilian electrical appliances.

Scrap copper clad laminates are defective products and scraps produced during the production process. They appear yellow due to the pressed copper foil on the surface, and are generally called yellow boards. The copper content of waste copper clad laminates varies from about 15% as low to more than 70%. It is an important resource for copper recovery.

2. Waste printed circuit boards

Printed circuit board is referred to as PCB. Usually, the conductive pattern made of printed circuits, printed originals or a combination of both on the insulating material according to the predetermined design is called the printed circuit, and the conductive pattern that provides the electrical connection between the components on the insulating substrate Call it a printed circuit. The printed circuit or the finished board of the printed circuit is called the printed circuit board.

Printed circuit boards are mainly used to provide support for the fixed assembly of various electronic components such as integrated circuits, to realize wiring and electrical connection or electrical insulation between various electronic components such as integrated circuits, and to provide solder mask patterns for automatic soldering, Provide identifying characters and graphics for component insertion, inspection, and maintenance.

Almost all electronic devices we can see have PCBs, such as calculators, computers, communication electronic equipment, military weapon systems, etc. As long as there are electronic components such as integrated circuits, PCBs are used for electrical interconnection between them. Common computer boards are basically double-sided printed circuit boards based on epoxy glass cloth. One side is for inserting components, and the other side is for component pin soldering. The solder joints are generally very regular.

The defective products produced in the production process of printed circuit boards are what we often call waste printed circuit boards. Because they are mainly green, they are also called green boards. In the production of printed circuit boards, although part of the copper has been corroded, and the copper content of the printed circuit boards is lower than that of the copper clad laminates, the printed circuit boards are still one of the resources for recycling copper.

3. Waste circuit board

Waste circuit board cards mainly come from various scrapped electrical appliances. There are many types. The common ones are green boards and yellow boards. Among them, green boards are mainly disassembled from discarded TV sets, computers, and communication equipment, and have high value; yellow boards It is mainly disassembled from tape recorders, audio equipment, washing machines, and air conditioners, and has low value.

The composition of waste circuit boards is more complicated. In addition to printed circuit boards, it also contains integrated circuits and various electronic components. The main components are silicon dioxide, copper foil, lead, tin, iron and trace precious metals and plastics, resins, Organic substances such as paint are therefore more difficult to handle than waste copper clad laminates and waste printed circuit boards.

2. Gravity beneficiation technology for processing waste circuit boards

This technology is based on the principle of gravity beneficiation. The waste board is first crushed to a certain particle size, and then water is used as a medium to treat it with a shaker, and finally achieve the purpose of separating reinforcing materials such as copper and glass fiber. The shaker is a bed surface with many parallel reciprocating strips or grooves in the longitudinal direction. It uses mechanical power to make asymmetrical reciprocating motion while working together with the thin inclined surface water flow to make the particles loose on the bed surface. The process of stratifying, zoning, and sorting minerals according to different densities. The final product of the gravity beneficiation method for processing waste copper clad laminates is copper powder, strictly speaking, a copper scrap with a diameter of about 20-40 mesh. Because the shaker is a kind of beneficiation equipment, the final product in the beneficiation process is concentrate, not pure metal, so the copper powder obtained by this method to treat waste circuit boards contains about 85% to 95% copper. If you deal with circuit boards that do not contain integrated circuits and components, the copper powder contains a small amount of iron, lead, and tin.

The raw material is firstly crushed by a crusher, and then enters the second crushing process, making it into crushed material with a particle size of about 20-40 mesh. The continuous addition of water during the crushing process not only serves as a cooling device, but also makes the scrap and water form a slurry, which not only avoids the dust pollution during the crushing process, but also facilitates the direct flow of the scrap into the next process. The slurry formed after crushing enters the shaker for gravity sorting. Under the action of vibration and gravity, the copper particles are separated from the broken glass fibers. The copper particles slip into a special collection tank and are taken out of the water at regular intervals and dried by a spin dryer., And then dried to obtain the final product copper powder. In order to increase the recovery rate, the materials passing through the first shaker must pass through the second shaker to further recover the copper in it. The quality of the copper powder obtained from the first shaker is better, with a copper content between 85% and 95%, and the copper powder obtained from the second time has higher impurities, and generally contains less than 80% copper. After separating the copper powder, the broken glass fiber slurry enters the multi-stage sedimentation tank for natural precipitation, and the water is recycled.
After many years of practice, it has been proved that gravity beneficiation technology has the best effect on processing waste copper clad laminates, followed by printed circuit boards, but it cannot deal with waste circuit boards. At present, some enterprises often use manual detinning in a simple detinning furnace before disposing of waste circuit boards, and after removing the electronic components, they are crushed. With the continuous development of electronic industry technology, the yield rate of copper clad laminates and the pass rate of printed circuit boards are constantly increasing, and the amount of waste copper clad laminates produced is gradually decreasing. At the same time, due to the increase in scrap electromechanical products, the number of waste circuit boards is also increasing rapidly. In the future, the number of waste circuit boards will be larger.

The use of gravity beneficiation technology to process waste circuit boards has the advantages of low investment and simple process, but it cannot directly process waste circuit boards. The copper powder produced by this technology contains high impurities and is not convenient for direct utilization. Moreover, the copper contains lead and tin, and the metal recovery rate is low. In addition, the resulting glass fiber fragments are difficult to handle and will have an impact on the environment during the accumulation process. At present, some companies try to make them into building materials such as bricks or process them into other materials, but these materials made with organic binders have a short lifespan, and once damaged, they will become pollution sources again.