The development boards we often get are covered with devices. Without a shell, to be precise, it is called PCBA.
And what we are talking about today is PCB, the Chinese printed circuit board, which is the carrier of the electrical connection of electronic components, and is an empty board that has not yet been SMT.
印刷电路板
The advantage of PCB is stability. After the electronic components are attached, the electrical connections are carried inside the circuit board. With the increase of the number of layers on the board, the circuit can be more complicated, that is, more functional circuits can be added.
And we use breadboard to pull wire ourselves, so students do small projects and study in the laboratory.
上大学时自己焊接的面包板
When we get the PCB board, you will find that the thickness is about 1mm. If you look carefully, you will see a lot of layers under this thickness of 1mm. The PCB is not made of a complete bare board, but made of many materials. Layer by layer laminated together.
The picture below is a lamination diagram of a 4-layer board. You can see that there are actually many materials inside.
PCB板的层压图示
There are several important concepts in the laminate structure of PCB boards.
Prepreg , Chinese prepreg, also known as PP, is one of the main materials in the production of multilayer boards, mainly composed of resin and reinforcing materials.
Reinforcing materials are divided into several types such as fiberglass cloth, paper-based, composite materials, and the prepregs (bonding sheets) used in the production of multilayer printed boards mostly use fiberglass cloth as reinforcement materials.
The prepreg is also called a prepreg. During lamination, the epoxy resin of the prepreg melts, flows, and solidifies, pressing each layer of circuits together to form a reliable insulating layer.
Core , Chinese core board, the core board is a hard, specific thickness, two-bread copper plate, which is the basic material of the printed board.
The laminated materials of the multilayer board are mainly Prepreg and Core .
OZ , the thickness of the PCB copper foil is in OZ. 1OZ means the thickness of copper with a weight of 1OZ evenly spread on an area of 1 square foot (FT2).
1oz = 35um = 0.035mm。
工作中的层压机器
After reading the above content, you already have a picture of PCB lamination in your heart. Then you can take a look at the following PCB board production introduction video, PCB board basic knowledge and lamination structure (video included)
Dielectric constant . When an electric field is applied to the medium, an induced charge will be generated to weaken the electric field. The ratio of the original applied electric field (in vacuum) to the electric field in the final medium is the dielectric constant.
The dielectric constant is also called the dielectric rate, which is related to frequency. The dielectric constant is the product of the relative dielectric constant and the absolute dielectric constant in vacuum. If a material with a high dielectric constant is placed in an electric field, the strength of the electric field will drop considerably in the dielectric, and the relative dielectric constant of an ideal conductor is infinite.
The following is the explanation of the dielectric constant of Huaqiang PCB.
The dielectric constant refers to the amount of electrostatic energy (Electrostatic Energy) that can be stored per unit volume of an insulating material under each unit of potential gradient.
There is another synonymous word "permittivity" (Permittivity is called Permittivity in Japanese). It is easier to understand the meaning literally. When the "permeability" of the insulating sheet is greater (indicating the worse the quality), and the two approaching wires are working with current, it is more difficult to achieve the effect of complete insulation, in other words, the more likely it is to produce a certain degree of leakage.
Therefore, the "dielectric constant" (or transmittance) of the insulating material should be as small as possible. At present, Teflon (PTFE) has the best dielectric constant measured at a frequency of 1MHz, and FR-4 is about 4.7.
PP sheet type
The following are several common types of PP films, 2116, 1080 and 7628 are commonly used now.
Recommend several common PCB laminate structures
The following are several common laminated structures of Huaqiang PCB. The lamination of each board factory may be different, and it is necessary to communicate with the board factory in detail when the board is launched.
4-layer board, finished board thickness 0.8mm
6-layer board, finished board thickness 1.2mm
6-layer board, finished board thickness 1.6mm
8-layer board, finished board thickness 1.2mm
Today's article is over here. I hope it will be helpful to you. See you in the next issue.
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