The critical temperature at which the pcb substratemelts from solid to rubber liquid is called Tg point, namely melting point. The higher the Tg point is, the higher the temperature requirement is when the plate is pressed, and the pressed plate will also be hard and brittle, which will affect the quality of mechanical drilling (if any) in the subsequent process and the electrical properties during use to a certain extent.
The melting point of a substance is the temperature at which the solid and liquid of a pure substance are in equilibrium under a certain pressure, that is, under this pressure and melting point temperature, the chemical potential of a pure substance as a solid is equal to the chemical potential of a pure substance as a liquid. For a pure substance solid system (nanometer system) with great dispersion, the surface part cannot be ignored. Its chemical potential is not only a function of temperature and pressure, but also related to the particle size of solid particles, It belongs to the first order phase change process of thermodynamics.
The melting point varies with pressure in two different ways. For most substances, the melting process is a process of increasing the volume. When the pressure increases, the melting point of these substances will rise; For substances such as water, unlike most substances, the volume of the process of ice melting into water should be reduced (so should metal bismuth, antimony, etc.). When the pressure increases, the melting point of ice should be reduced.
Reference: Melting point_ Baidu Encyclopedia
Tg: Glass Transition Temperature, which refers to the Temperature at which the glassy substances transform into each other between the glassy state and the high elastic state (commonly referred to as softening). In the industry, this glassy substance generally refers to the medium layer composed of resin or resin and Glass fiber cloth.
How to distinguish PCB from fake
1. Identify the formal big brands
If you want to buy real PCB boards, you have to buy boards of formal brands. After all, brands are carriers of quality and strength. If big brands want to have long-term development in the industry, they must pay attention to their brand image, and will never risk doing something that will damage their reputation.
2. See the grade of environmental protection signs
To distinguish the authenticity of PCB materials, we can see the grade of the environmental protection logo. Generally, when I buy boards, there will be an inkjet code on the top and side of the board, and the environmental protection grade of building materials will be clearly marked on the inkjet code, from which we can make a basic judgment.
3. Look at the plate price
Because PCB grade has the advantage of low formaldehyde emission, PCB grade boards will definitely be much more expensive than E1 and E2 grade boards. Therefore, if you decide to buy PCB grade boards, you must not just think about saving money and covet cheap boards. You should know that "cheap boards are not good, and good boards are not cheap".
4. View the quality inspection report of the sheet
If you really don't know how to check the authenticity of PCB boards, there is one of the most direct, reliable and effective ways, which is to let the seller show the national test report.
Reference: Baidu Encyclopedia TG
1. The critical temperature at which the substrate melts from solid to rubber liquid is called Tg point, namely melting point
2. The higher the Tg point is, the higher the temperature requirement is when the plate is pressed, and the pressed plate will be hard and brittle, to a certain extent
It will affect the quality of mechanical drilling (if any) in the subsequent process and the electrical characteristics when used.
3. Tg point is the highest temperature (℃) at which the base material remains rigid. That is to say, common PCB substrate materials not only soften
Deformation, melting and other phenomena, as well as the sharp decline of mechanical and electrical characteristics
4. Generally, the Tg of the plate is more than 130 degrees, the High Tg is more than 170 degrees, and the medium Tg is more than 150 degrees; The Tg of the substrate is increased, and the heat resistance, moisture resistance, chemical resistance, stability resistance and other characteristics of the printed board will be improved. The higher the TG value is, the better the temperature resistance of the plate is. Especially in the lead-free tin spraying process, high Tg is more widely used.
Product name: Glass transition temperature
English name: glass transition temperature
English abbreviation: T G
Note: The temperature at which a polymer changes from a highly elastic state to a glassy state refers to the temperature at which an amorphous polymer (including the amorphous part of a crystalline polymer) changes from a glassy state to a highly elastic state or from the latter to the former. It is the lowest temperature at which a macromolecular segment of an amorphous polymer moves freely, usually expressed as T G. There is no very fixed value, which often changes with the measurement method and conditions. An important process index of polymer. Above this temperature, the polymer shows elasticity; Below this temperature, polymers show brittleness, which must be considered when used as plastics, rubber, synthetic fibers, etc. For example, the glass transition temperature of PVC is 80 ℃. However, it is not the upper limit of product working temperature. For example, the working temperature of rubber must be above the glass transition temperature, otherwise it will lose its high elasticity.
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