Circuit board. Underside of a PCB (printed circuit board). A PCB consists of lines (dark blue) of a metal conductor printed on an insulating material base. The metal lines form a circuit that connects the electronic components which are added to make a functioning device. The components are plugged into the board with pins that are held in place by solder (shiny round lumps), a soft metal that can easily be melted for this purpose. Circuit boards are used in most electronic products, including computers. This is a circuit board that is used in a video tape recorder. The triangular symbols (centre right) indicate the presence of electronic components called diodes.