The introduction of the Structure of PCB(Printed circuit boards)
There are three forms of PCB: single-sided, double-sided, or multilayer. The physical property can be either rigid, flexible, or a combination of both. Irrespective of the both PCB consists of three basic parts: 1) a non-conducting substrate or laminate;2) conductive circuits printed on or inside the substrate; and3) mounted components. Of the several types of substrates used in PCBs, the most widely used one is the (Flame Retardant) FR4, which is made up of glass fiber reinforced epoxy resin with a brominated flame retardant in the epoxy matrix. Another widely used laminate is the FR2 laminate that is made up of paper reinforced phenolic resin with added flame-retardants. Some other types of laminates/substrates are discussed in. Conductive circuits used in most application are produced
using copper. PCB tracks are made by protecting the copper, that is needed for conductive purpose, with an etch resistant material and then exposing the whole board in an etching solution. Elements such as nickel, silver, tin, tin-lead, and gold are used as etch-resistant. The resin type and the reinforcement
used in PCB can affect its electrical and thermo mechanical performance. As discussed in, resins used for high-performance PCB offer higher Tgs and lower -axis-expansions for improved through-hole reliability and non-halogenated epoxy resin systems are used for the production of green PCBs.
The components mounted on PCBs generally include chips, connectors, capacitors, etc. Different components have a different material composition. For instance Tantalum is used in capacitors, elements such as Ga, In, Ti, Si, Ge, As, Sb, Se, and Te can be found in chips and other units. Solder joints contains An, Pb and Cd whereas bridges and slots on boards are made of ceramics including, Al2O3, BeOand glasses. Semiconductors contain Ga, Si, Se, Ge, and other elements in smaller quantities. A 1995 Nordic investigation analyzes metal content of PCBs and more can be found in. Material composition of PCBs is, therefore, quite complex and causes problem for the recycling industry.