The printed circuit board (PCB) has been in use for over a century, but it is still one of the most important parts of electronic devices, as the circuitry links all components together into an economical and efficiently integrated system. Once called printed wiring since they were first used to replace hand wiring in early telephone switchboards and radios, printed circuit boards are now ubiquitous. The printed circuit board consists of patterned arrays of conductors, such as copper, that are held onto and within dielectric materials, such as epoxy. But many other materials are used with dozens of processes to produce a myriad of circuit types that enable thousands of products.