What is pcb? What is the impact on the environment?

Expired printed circuit boards are difficult to degrade. Refractory pollutants containing heavy metals will cause PCB pollution if they are disposed at will. The design and production of printed circuit board is mainly to remove excess copper from copper clad laminate to form a circuit. Multilayer printed circuit boards also need to connect and conduct all layers. As the circuit board becomes finer and smaller, and the machining accuracy becomes higher and higher, the production of printed boards becomes more and more complicated. There are dozens of processes in its production process, and chemicals enter the wastewater in each process. The pollutants in PCB design and production wastewater are as follows: 1. copper. Because the excess copper is removed from the copper clad laminate, leaving the circuit, copper is the most important pollutant in the wastewater of printed circuit board design, and copper foil is the main source. In addition, because the circuits of each layer of double-panel and multi-layer board need to be connected, the circuits of each layer are connected by drilling holes and copper plating on the substrate, while the first layer of copper plating (usually resin) on the substrate and the intermediate process of electroless copper plating use complex copper to control the stable copper deposition speed and thickness. EDTA-Cu (sodium copper ethylenediamine tetraacetate) is generally used, but there are also unknown components. PCB cleaning water after electroless copper plating also contains complex copper. In addition, there are nickel plating, gold plating and tin-lead plating in PCB production, so they also contain these heavy metals. Second, organic matter. In the process of making circuit patterns, copper foil etching, circuit welding, etc. Cover the copper foil to be protected with ink and put it back after it is finished. These processes produce high-concentration organic compounds, some of which have COD as high as10 ~ 20g/L. These high-concentration wastewater accounts for about 5% of the total water, and it is also the main source of COD in PCB production wastewater. Third, ammonia nitrogen. According to different production processes, some etching solutions contain ammonia water and ammonium chloride, which are the main sources of ammonia nitrogen. Fourth, other pollutants. In addition to the above major pollutants, there are acids, alkalis, nickel, lead, tin, manganese, cyanide ions and fluorine. In PCB production, sulfuric acid, hydrochloric acid, nitric acid and sodium hydroxide are used, as well as dozens of commercial chemical solutions such as etching solution, electroless plating solution, electroplating solution, activation solution and pre-immersion solution. The composition is complex, except for most known components, there are a few unknown components, which makes wastewater treatment more complicated and difficult.