PCB substrate is composed of copper Foil layer (Cooper Foil), Reinforcement material (Reinforcement), resin (Epoxy) and other three main components, since the Lead Free (Lead Free) process began, the fourth powder (Fillers) was added to the PCB board in large quantities. In order to improve the heat resistance of the PCB.
We can think of copper foil as the blood vessels of the human body, used to transport important blood, so that PCB has the ability to move; The reinforcing material can be imagined as the human skeleton, which is used to support and strengthen the PCB to avoid soft collapse; The resin can be imagined to be the muscle of the human body and is the main component of the PCB.
Let's talk about the use, characteristics and precautions of these four PCB materials.
1、Copper Foil
Electric Circuit: a circuit that conducts electricity.
Signal line: A signal line for transmitting a message.
Vcc: power layer, operating voltage. The working voltage of the earliest electronic products is mostly set to 12V, with the evolution of technology, the requirements of power saving, the working voltage has slowly become 5V, 3V, and now it is gradually moving to 1V, and the relative requirements of copper foil are getting higher and higher.
GND(Grounding) : grounding ground. Vcc can be thought of as a water tower, when the faucet is opened, water (electrons) will flow out through the pressure of water (working voltage), because the action of electronic parts is determined by the flow of electrons; GND, on the other hand, can be thought of as a sewer through which all used or unused water flows.
Heat Dissipation: Heat dissipation. Most electronic components will consume energy and generate heat, at this time, it is necessary to design a large area of copper foil to let the heat energy be released into the air as soon as possible, otherwise not only humans can not stand, even electronic parts will follow the machine.
2、Reinforcement
The selection of PCB reinforcement material must have the following excellent characteristics. Most of the PCB reinforcing materials we see are made of Glass Fiber (GF, Glass Fiber), if you look carefully, the material of glass fiber is a bit like a very thin fishing line, because it has the following personality advantages, so it is often chosen as the basic material of PCB.
High Stiffness: Has a high stiffness, so that the PCB is not easily deformed.
Dimension Stability: Good dimensional stability.
Low CTE: Has a low thermal expansion rate to prevent the PCB internal line contacts from breaking away and causing failure.
Low Warpage: With low deformation, that is, low plate bending, plate warping.
3、Resin Matrix
Traditional FR4 plates are Epoxy based, LF(Lead Free)/HF(Halogen Free) plates are made of a variety of resins and different curing agents, making the cost rise, LF about 20%, HF about 45%.
HF plate is brittle and easy to crack and water absorption becomes larger, thick and large plate is prone to CAF, it is necessary to change to open fiber cloth, flat fiber cloth, and strengthen the material containing uniform immersion.
A good resin must have the following conditions:
Heat Resistance: Good heat resistance. After heating and welding for two to three times, the board will not explode, and the heat resistance is good.
Low Water Absorption: low water absorption. Water absorption is the main cause of PCB explosion.
Flame Retardance: Flame retardance must be present.
Peel Strength: High tear strength.
High Tg: High glass transition point. Most materials with high Tg are not easy to absorb water, and non-absorption is the root cause of non-explosive plates, not because of high Tg.
Toughness: Good toughness. The tougher the board, the less explosive. Toughness is also known as the energy of destruction, and the better the toughness of the material, the stronger its ability to withstand impact and damage.
Dielectric properties: High dielectric properties, i.e. insulation material.
4、Fillers System
In the early lead welding, the temperature was not very high, and the original PCB board could be tolerated. Since the temperature was increased after lead-free welding, powder was added to the PCB board to make the PCB resistant to temperature.
Fillers should be coupled first to improve dispersity and cohesiveness.
Heat Resistance: Good heat resistance. After heating and welding for two to three times, the board will not explode, and the heat resistance is good.
Low Water Absorption: low water absorption. Water absorption is the main cause of PCB explosion.
Flame Retardance: Flame retardance must be present.
High Stiffness: Has a high "stiffness" so that the PCB is not easily deformed.
Low CTE: Has a low thermal expansion rate to prevent the PCB internal line contacts from breaking away and causing failure.
Dimension Stability: Good dimensional stability.
Low Warpage: With low deformation, that is, low plate bending, plate warping.
Drill processibility: The difficulty of PCB drilling is caused by the high rigidity and toughness of the powder.
Heat Dissipation(due to high thermal conductivity) : Heat dissipation.
