PCB Classification, Do You Understand All???

 

In the electronic devices we use in our daily life, such as remote controls, mobile phones, refrigerators, televisions, air conditioners, computers... Etc., there is an important part called "Circuit Board", but its official full name should be "Printed circuit board", because the formation of its electronic circuit (circuits) is really similar to early book printing, so its English abbreviation is "PCB (Printed Circuit Board)", It is also abbreviated as "PWB (Printed Wire Board)".

 

 

 

In short, the PCB is like the base of the electronic device, responsible for connecting all the electronic parts in the same network, so that they can work together.

 

 

You can think of the PCB as the chassis of a car, and all the components of the car are installed on it, and they can work together. However, I personally feel that PCB is more like a piece of urban land with a road already built in the urban plan, waiting for other agency buildings to be stationed in a fixed location. The town that has been developed is a PCBA(Printed Circuit Board Assembly), which we usually call "assembled circuit board" or "assembled board".

 

 

The main body of the PCB is a hard board with a thickness of about 1.0mm~1.6mm, depending on the design needs, sometimes the thickness of the PCB will be thinner or thicker, and some will be specially designed as a flexible board (FPCB) that can be bent and bent. For some more special needs, rigid and flexible boards will be combined at the same time to become rigid-flex board (rigid-flex board).

 

 

 

On top of the board is one or more layers of conductive metal, usually copper foil, cleverly designed to form a network (electronic circuit), much like the streets of a town, allowing the different components in the electronic device to communicate and collaborate.

 

 

 

These components can be passive resistors, capacitors, inductors and other components, or active transistors, integrated circuits (ics), and they all have their own functions. When these parts are connected together through the metal network on the PCB, a complete circuit is formed, just like the connection of the building organs in various locations in the city, and the power supply will start to operate in accordance with the design.

 

 

 

In summary, PCB enables the various components in electronic devices to cooperate in an organized way to achieve the functions we need, such as playing music, displaying pictures, sending messages, and so on. This is the basic role of PCB in electronic equipment.

 

 

 

At present, the circuit board on the market is mainly classified into hard circuit board, flexible circuit board and soft and hard composite circuit board three categories.

 

 

Rigid Printed Circuit Board

The basic reason for this classification of PCB is that most board factories are based on the production of hard circuit boards, and the market demand for hard boards is also the largest, because the most important use of PCB in addition to transmitting electronic signals, but also used to support the installation of electronic parts, electronic parts usually use solder to fix on the PCB, and solder can not withstand too much bending or deformation stress. Otherwise, it is easy to break, and may even cause damage to the electronic parts themselves. This is why I have a number of articles to explore the causes of solder cracking and countermeasures.

 

 

 

Because most of the printed circuit boards are hard boards, we generally use "circuit board (PCB)" to represent the hard circuit board.

 

 

 

The hard board consists of a single or multi-layer circuit board covered with conductive copper foil on an insulating substrate (usually a glass fiber cloth with certain strength and rigidity).

Flexible Printed Circuit Board

 

 

Flexible Printed Circuit Board (FPCB or FPC). FPC is made by covering conductive copper foil on a polymer film (which can first be thought of as a material similar to plastic bag film).

 

 

 

The biggest advantage of FPC is its winding and easy to bend characteristics, so FPC is very suitable for use in some limited space, can not use a single PCB to meet all the design needs of the product, some products may need to overlap multiple PCB, so the FPC can be bent to connect, some may be in order to save the cost of the plate. Use soft boards for remote signal connections.

 

 

 

So the biggest use of FPC is to connect the electronic signals of different PCBS together.

 

 

 

However, because the FPC can be wound, it can not bear the electronic parts to be welded on it, but the problem is man-made, smart engineers came up with a hard reinforcement plate under the FPC, so that you can not be afraid of FPC bending caused by the solder crack.

 

 

 

Compared with hardboard PCB, FPC is not suitable for designing complex circuits and welding precision electronic parts.

 

Rigid-Flex PCB

 

 

The main purpose of the soft board (FPC) is to connect different hard boards (PCB), but in order to fix the soft board on the hard board, the soft board is usually welded directly to the hard board using a connector or HotBar technology, but it is necessary to retain a certain space on the hard board for the connector or soft board welding position. This is less and less space for those products with smaller and smaller sizes and higher and higher parts density, so some people came up with the idea of combining the soft board with the hard board to form a "Rigid composite board (Rigid flex PCB)", so that it should be able to release the connector or soft board welding space for other parts.

 

 

 

Just the idea is very beautiful, "soft and hard composite board" also does have many advantages, such as saving space, reducing electronic signal transmission loss, simplifying assembly steps to reduce working hours, but the reality is cruel, because the unit price of soft and hard composite board is not cheap, the actual cost of operation down than soft board + hard board + connector is also expensive, In addition, the SMT production has to use the furnace tray (carrier) to support the soft board, and the maintenance is not convenient.

 

 

 

"Soft and hard composite panels" are generally only used in some higher-order products, or product design has inherent limitations. Therefore, "soft and hard composite board" can be used as an option on the design and process.

 

 

 

In addition to the above classification methods, there are also the following divisions of PCB:

 

Classified by surface treatment: OSP, gold plating, ENIG(gold/gold precipitation), HASL(tin spray), ImSn(tin), ImAg(silver).

 

 

Classified by product application: computer board, communication board, vehicle board, consumer electronics board, electronic assembly board (IC carrier board).

 

 

 

Classification by the number of circuit layers: single panel, double panel, multi-layer board.

 

 

 

Classified by substrate: plastic substrate board, ceramic substrate board, metal core substrate (aluminum substrate, copper substrate... Etc.).

 

 

 

It is classified by the Through Hole structure: through hole board (Plating-Through-Hole board), micro-via board (micro-via board), blind hole board, high-density board (HDI board).