WHAT IS PCB AND ITS TYPES?

   As electronics moved from vacuum tubes and relays to silicon and integrated circuits, the size and cost of electronic components began to decrease. Electronics became more prevalent in consumer goods, and the pressure to reduce the size and manufacturing costs of electronic products drove manufacturers to look for better solutions. Thus was born the PCB.

       PCB is an acronym for printed circuit board. It is a board that has lines and pads that connect various points together. In the picture above, there are traces that electrically connect the various connectors and components to each other. A PCB allows signals and power to be routed between physical devices. Solder is the metal that makes the electrical connections between the surface of the PCB and the electronic components. Being metal, solder also serves as a strong mechanical adhesive.

  PCBs may be classified in many different ways according to their various attributes. One fundamental structure common to all of them is that they must provide electrical conductor paths that interconnect components to be mounted on them.

There are two basic ways to form these conductors:

1.   Subtractive. In the subtractive process, the unwanted portion of the copper foil on the base substrate is etched away, leaving the desired conductor pattern in place.

2.   Additive. In the additive process, formation of the conductor pattern is accomplished by adding copper to a bare (no copper foil) substrate in the pattern and places desired. This can be done by plating copper, screening conductive paste, or laying down insulating wire onto the substrate on the predetermined conductor paths.

(1) Single sided PCB

  Single sided board means the conductor pattern appears only on one side. Because single sided PCB has many strict limits. On trace design, only circuit at early stage use this kind of boards.

(2) Double sided PCB

   Double sided board means the conductor patterns appear on both sides of the board. However if we use the conductor patterns on both sides, there should be proper circuit to connect two sides. The bridge between the circuits is called via. Those vias are plated with metal, such as tin, copper, gold, etc. Because the area of double sided PCB is two fold of the area of single sided, and the conductor pattern can cross with each other, so it suits to be used on more complex circuits.

(3) Multi-layer boards

   In order to enlarge the area of conductor pattern, multilayer PCB uses more single or double boards. It uses several piece of double sided boards, and a dielectric layer is put between every layer of boards. The layers of one PCB represent the layer of conductor patterns. The amount of the layers is always even number. Technically we can make PCBs up to 100 layers.

   For via, if we use it on double sided PCB, the whole boards will be drilled. While on multilayer PCB, if you just want to connect some traces, via may will waste trace space of some layers. Then we use buried vias and blind vias to solve this problem, because they are only drilled through several layers.

a. Buried vias only connect inner PCBs, so we can’t see them from the surface.

b. Blind vias connects several layers PCB with surface PCB.

   In multilayer PCB, the whole board directly connects the ground line and power (used for preventing affection of the transmission signals on the signal). So we divide layers into signal, power, or ground. If the components on PCB need different power supply, this kind of PCB would have more than two layers of power and wire layers.