printed circuit boards (PCB) form the base of the electronic circuit cards that operate and control video, audio, computer and industrial devices. The raw boards are made of flat fiberglass panels coated on one or both sides with copper. They are called printed circuit boards because the circuit design is photo-printed onto the board before it is processed into a circuit card. Designing Circuits Etching Process Solder Spots PCB History
The first step in turning a PCB into a circuit card is designing the circuit. An engineer draws a schematic diagram showing the electronic components that will populate the card and how those components will be connected. Once the design is completed, computer programs translate the schematic symbols into physical components and actual electrical pathways. The computer generates a film "mask" with the circuit layout and component connections in the actual places they belong.
The next step is to take an industry-standard 0.059-inch-thick PCB and lay the circuit mask on top of it. A computer-controlled device drills mounting holes for the components at the spots indicated by the mask, then electroplates copper into each hole. The circuit image is applied to the board by first coating it with a photosensitive film, laying the mask over the board and exposing the board to intense light. Then tin is electroplated on to the board. The tin sticks only to the areas shielded from light by the mask. The board then is dipped into an acid solution that eats away the areas not coated with tin.
The board is covered with another mask that has holes where solder is to be applied to attach the electronic components. The board is dipped into molten solder that sticks to the board at the holes in the solder mask. The solder mask becomes a permanent part of the board, giving the board its characteristic green color. A silkscreen printing process applies numbers, letters and shape outlines that identify where each electronic component goes. The completed board then goes to an assembly house where the electronic components will be installed on the board and the board assembled into the final product.
Printed circuit boards were invented in 1936 in Austria by engineer Paul Eisler, who used them to build radio sets, says the schmartboard.com website. The United States and its allies used printed circuit board technology to produce huge numbers of hand-held two-way radios in World War II. In 1948, the United States declassified printed circuit technology, releasing it into the consumer electronics marketplace. Printed circuit boards saw growing acceptance in the 1950s despite difficulties in soldering components to the boards. In the mid-1960s, IBM engineers perfected surface-mount technologies that greatly simplified design and fabrication processes for the boards. As a result, these boards have become the heart of virtually all consumer electronics products.
