The Introduction of structure and function of PCB board
Nowadays, the PCB base material is composed of Copper Foil, Reinforcement, resin and other three main components. However, since the Lead Free process began, the fourth Fillers were added into the PCB plates in large quantities to improve the heat resistance of PCB.
1. Copper Foil
Electric Circuit: A Signal line that transmits a message.
Vcc: power layer, working voltage. The working voltage of the earliest electronic products was mostly set as 12V. With the development of technology and the requirement of power saving, the working voltage gradually changed to 5V and 3V, and now it is gradually moving to 1V. The requirements of copper foil are also higher and higher.
GND (Grounding) : the ground plane. The Vcc can be thought of as the water tower at home. When we turn on the faucet, water (electrons) will flow out through the water pressure (working voltage), because the movement of electronic parts depends on the flow of electrons. GND, on the other hand, can be thought of as a sewer. All used or unused water goes down the drain.
Heat Dissipation (due to high thermal conductivity) : Heat Dissipation. Have you ever heard that some cpus are hot enough to cook an egg? This is not an exaggeration. Most electronic components use energy to generate heat.
2. Reinforcement (Reinforcement material)
When selecting PCB reinforcement material, it must have the following excellent characteristics. Most of the PCB reinforcement materials we see are made of GF (Glass Fiber). If you look closely, the material of Glass Fiber is a little like a very thin fishing line. Due to the following personal advantages, it is often used as the basic material of PCB.
High Stiffness, High "rigid", let the PCB is out of shape not easily.
Dimension Stability: good dimensional Stability.
Low CTE: with a Low "thermal expansion rate" to prevent the connection points inside the PCB from detaching and causing failure.
Low Warpage: with Low deformation, that is, Low plate bending and plate warping.
-sheldon: young's High Modules.
3. Resin Matrix
Conventional FR4 sheets are dominated by Epoxy, and LF(Lead Free)/HF Free sheets are made with a variety of resins and different curing agents, resulting in cost increases of about 20% LF and 45% HF.
HF plates are brittle and cracked, and their water absorption rate increases. CAF is easy to occur in thick and large plates. Therefore, fiber cloth and flat fiber cloth should be adopted instead, and materials containing even immersion should be strengthened.
Good resin must have the following conditions:
Good Heat Resistance. Heating welding after two to three times will not burst plate, good heat resistance.
"Low Water Absorption" : Water absorption is the main cause of PCB explosion.
Flame Retardance: Flame Retardance is a must.
Peel Strength: high Peel Strength.
High Tg: High glass transition point. Tg high materials are not easy to absorb water, not absorbing water is not the root cause of the plate, not because of high Tg.
Toughness: good Toughness. The greater the toughness, the less vulnerable the plate. Toughness is also referred to as "Toughness energy". The tougher the material, the more resilient it is to withstand the impact and resistance.
Dielectric properties: high Dielectric properties, namely insulating materials.
4. Fillers System (powder, Fillers)
In the early days, the temperature was not very high when there was lead welding, and the original board of PCB was still tolerable. Since the lead-free welding, the temperature increased, so the powder was added into the board of PCB to provide strong resistance to the temperature of the material.
Fillers should be coupled first to improve dispersion and density.
Heat to hold
Low Water Absorption
Drill processability: due to the high rigidity and toughness of powder, PCB drilling is difficult.
High Modulus, young's Modulus
Heat Dissipation (due to high thermal conductivity) : Heat Dissipation.