Classification

Single panel

On the most basic PCB, parts are concentrated on one side and wires are concentrated on the other side. Because wires only appear on one side, this type of PCB is called a single side. Because single panels have many strict restrictions on the design of wiring (as they only have one side, wiring cannot cross and must be routed independently), only early circuits used such boards

Double sided board

This type of circuit board has wiring on both sides, but to use wires on both sides, it is necessary to have appropriate circuit connections between the two sides.

. The "bridge" between these circuits is called a guide hole (via). A guide hole is a small hole filled or coated with metal on a PCB that can be connected to wires on both sides. Because the area of the double-sided board is twice that of a single panel, the double panel solves the difficulty of staggered wiring in a single panel (which can be connected to the other side through guide holes), making it more suitable for use in more complex circuits than a single panel In order to increase the area that can be wired, multi-layer boards use more single or double-sided wiring boards. A printed circuit board that uses one double-sided inner layer, two single-sided outer layers, or two double-sided inner layers, and two single-sided outer layers, and is interconnected with conductive graphics according to design requirements through positioning systems and insulating bonding materials, becomes a four or six layer printed circuit board, also known as a multi-layer printed circuit board. The number of layers on a board does not necessarily represent several independent wiring layers. In special cases, empty layers are added to control the board thickness. Usually, the number of layers is even and includes the outermost two layers. Most motherboards have a structure of 4 to 8 layers, but theoretically, they can achieve nearly 100 layers of PCBs. Large supercomputers mostly use multiple layers of motherboards, but because these types of computers can now be replaced by clusters of many ordinary computers, ultra multi layer boards are gradually no longer used. Because the layers in a PCB are tightly integrated, it is generally not easy to see the actual number, but if you carefully observe the motherboard, you can still see it

Recycling

The manufacturing technology of printed circuit boards is a very complex and comprehensive processing technology. Especially in the wet processing process, a large amount of water needs to be used, resulting in the discharge of various heavy metal wastewater and organic wastewater, which have complex components and are difficult to treat. Calculated based on the utilization rate of copper foil on printed circuit boards ranging from 30% to 40%, the copper content in waste liquid and wastewater is considerable. Calculated based on 10000 square meters of double-sided boards (with a copper foil thickness of 35 microns on each side), the copper content in waste liquid and wastewater is about 4500 kilograms, as well as many other heavy metals and precious metals. These metals present in waste liquid and wastewater are discharged without treatment, which not only causes waste but also pollutes the environment. Therefore, the treatment of wastewater and the recovery of metals such as copper in the production process of printed boards are very meaningful and indispensable parts in printed board production