A printed circuit board, or PCB, is a self-sufficient unit of interconnected electronic components like capacitors, resistors or ICs found in devices ranging from common house hold electronic devices, or pagers, and radios to sophisticated radar and computer systems.
Vacuum tubes were king in older times of electronics; electronic devices were made up of components that were connected together by soldering them either to each other to terminal strips and tube sockets. Now day’s printed circuit boards have replaced all of them because of their reduced size and cheaper prices. Today, just about each and every electronic appliance in your home contains a printed circuit board of some type: computers, laptops, printers, mobile phones, TV, washing machines, refrigerators, musical instrument or coffee makers and digital clocks, microwave ovens, telephone answering machines.
Printed circuit boards (PCBs) are thin boards made from an insulating material, with a metal coated surface, sometimes on both the top and bottom. Etches are made in the metal with acid to create pathways for electricity to travel among various components which are surface mounted on the board with solder.
Printed circuit board assembly consists of multiple step process. After the printed circuit board (PCB) is completed, electronic components must be attached to form a functional printed circuit assembly, components are attached either by surface mount technology (SMT) or through hole technology. In surface-mount (SMT – surface mount technology) construction, the components are placed on pads or lands on the outer surfaces of the PCB and in through-hole construction, component leads are inserted in holes. Component leads are electrically and mechanically attached to the board with a molten metal solder in both types of construction.
Different soldering techniques are used to attach components to PCB.SMT placement machines or reflow ovens are used for high volume productions .small volume prototypes are done by skilled technicians by hands under a microscope ,using tweezers and a fine tip soldering iron.
In test procedure, the assembled printed circuit boards are placed into a fixture that brings electrical power to the boards to make them live functioning boards.
All active boards is then placed into an environmental stress system (ESS) chamber that will cycle between high and low temperature regimes for a number of cycles to determine if these stresses will initiate failures in the assembled boards. Rework has to be done if board fails the test and technicians may be solder and replace failed components.