Printed circuit board

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Printed circuit board with components attached

A printed circuit board (PCB) is a plastic board made for connecting electronic components together. These are used in almost all computers and electronics today.

The "card" is made of a material that does not conduct electricity, like fiberglass or plastic. Usually copper is etched (set in thin lines) inside the board between the layers of plastic, or on the surface of the board. [1] This makes the electricity go only where it is wanted.

Electronic components are then attached to this board using a metal to conduct electricity. The metal etched into the board allows electricity to travel from one component to another in electrical circuits.

Boards can have many different parts which are connected and work together. The most common circuit boards are made in large numbers for a specific job, for example to run a computer, a mobile/cell phone or a television. Some circuit boards are made plain so a person can build their own for a new electrical task. Most things that use electricity have at least one circuit board inside of them that makes them run.

Flexible circuit boards are those that are made thin enough and of the right material to flex (bend).

History[change | change source]

A hand made circuit board

Printed circuit boards came from electrical connection systems that were used in the 1850s. Originally metal strips or rods were used to connect large electric components mounted on wooden bases. Later, the metal strips were replaced by wires connected to screw terminals, and wooden bases were replaced by metal frames. This let things be smaller, which was needed as circuits became more complex with more parts. Thomas Edison tested methods of using metals on linen paper. Arthur Berry in 1913 patented a print-and-etch method in Britain. In 1925, Charles Ducas of the United States developed a method using electroplating. He created an electrical path directly on an insulated surface by printing through a stencil (a shape cut into a board or paper) with special ink that could conduct electricity, just like wires could. This method was called "printed wiring" or "printed circuit."

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Manufacturing[change | change source]

Photoresist[change | change source]

Most circuit boards are made with a light sensitive covering, for photolithography. This covering is sometimes called photo-resist. The covering reacts with light. Then the circuit board and covering are put in a developer. Developer is a liquid that dissolves the covering that was exposed to light. Then the board is put in an etchant. An etchant dissolves the copper that is not covered by the covering. Then the board is put into another liquid that removes the covering. Controlling what parts are exposed to light will control what copper is left. [2] Some companies also use this method. It is expensive per board, but very cheap to set up in the beginning.

Silkscreen[change | change source]

Some professionally made circuit boards use a different method to remove extra copper from the circuit board. A process called silk-screening is used. Silk-screening is when a cloth is pulled tight over a frame. Then an image is printed onto the cloth. Then ink is pressed through the cloth. The ink does not go where the image has been printed on the cloth. It is called silk-screening because the cloth is usually silk. The cloth is usually silk because it has very small holes. silk-screening is used to print an ink called resist onto the board. Resist is an ink that resists the etchant used to make the circuit board. Etchant dissolves the copper on the board. This is cheaper for each board than photo-resist, but is more expensive in the beginning.

Milling[change | change source]

Another way to make a circuit board is to use a mill. A mill is a drill that moves in many directions. The drill removes a small amount of copper each time it moves. The mill removes the copper around the wires on the board. This leaves extra copper on the board. Other methods do not leave the extra copper on the board. This method is cheaper per board, but the equipment to make it is expensive. It is also not commonly used in professionally made boards, because the first two ways are better.

Notes[change | change source]

  1. Rozenblat, L. (2008). PCB Printed Circuit Board Design – Guidelines, Layout Tutorials, Software. Retrieved April 26, 2009, from [1]
  2. (2009, March 9). In-house PCB Manufacture. Retrieved April 26, 2009, from [2]