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PCB

PCB : printed circuit board: what is it?

 

PCB is an abbreviation for printed circuit board. It is a board which has lines and pads connecting various points together. A PCB allows power and signals to be routed between physical devices.

 

Printed Circuit Board

Printed circuit board – also called “printed wiring boards – were initially constructed through a difficult process of point-to-point wiring. This process led to frequent failures at wire junctions and caused short circuits when wire insulation started aging and cracking. This was improved with the development of wire wrapping, where a gas-tight connection is created small gauge wire is wrapped around a post at each connection point, so this is more durable.

The size and cost of electronic components began to drastically decrease when electronics moved from vacuum tubes and relays to silicon and integrated circuits. PCB became extremely important because electronics became more prevalent in consumer goods, and manufacturers started to look for ways to reduce the size and manufacturing costs of electronic products.

PCB

 

Composition of the PCB

A PCB is composed of alternating layers of different materials – like layers of lasagna or cake- which are laminated together with heat and adhesive into a single object. There are several components of the PCB as detailed below:

  • FR4: The base substrate or material which is commonly fiberglass. This solid core provides the PCB with rigidity and thickness. Cheaper PCBs can be made of other materials like epoxies which lack the durability of FR4 but are much cheaper.
  • Copper: The next layer is the thin copper foil that is laminated to the board using heat and adhesive. In PCBs, copper can be applied to both sides or only a single side of the substrate
  • Soldermask: The layer on top of the copper foil is called the soldermask layer. This layer gives the green color of PCB. It’s used for insulating the copper traces and preventing any accidental contact with other metal or solder bits by overlaying the solder mask onto the copper layer. It helps solder to the correct places and prevents solder jumpers.
  • Silkscreen: Silkscreen is the white layer applied on top of the soldermask layer. The silkscreen is used to adds letters or symbols to the PCB to allow  easier assembly and indication of function or part.

 

Chemical Etching

Chemical etching divides the copper into separate conducting lines called tracks which function as wires fixed in place. The pattern etched into each copper layer of the PCB is called the artwork. A PCB can be a two-layer board with a copper layer on both sides or even a multi-layer board where additional copper layers are sandwiched between layers of insulating material.

THT in PCB

SMT

Components can be mounted in two ways. Through hole components are mounted by passing the wire leads through the board and soldering them to traces on the other side. Surface mount components are soldered by their leads to copper traces on the same side of the board.

 

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