PCB Materials Guide: Grades, Types and Electrical Properties
For almost all printed circuit board manufacturers, the preparation of PCB materials is a necessary step. If you want to produce high-quality PCBs, the choice of PCB materials is very important. Therefore, we will provide you with guidance on the grades, types and electrical properties of printed circuit board materials. We hope this will be helpful to you.
The Grade of PCB Materials
According to the price of PCB materials and PCB finished products, PCB manufacturers’ choice for PCB materials is also different. if you want to pursue cost-effective PCB materials, then it is necessary to understand the different grades of PCB materials. The higher the grade of materials are often more expensive, and the applicable PCB is more and more complex.
The Types of PCB Materials
There are many types of printed circuit board materials, and different types are suitable for different PCBs, mainly the following:
Electronic/high-speed Materials:?Polyimide (PI), Polyphenylene oxide composites, Modified epoxy composites, Epoxy BT resin, Phenolic polyester fiberboard.
Microwave PCB Materials:?Liquid crystalline polymer (LCP), Hydrocarbon, Polytetrafluoroethylene polymer board (PTEF), PTEF glass-fibre fabric substrate, PTEF PCB substrate.
Resin Materials:?PTEF (Dk@1MHz: 2.1; Df@1MHz: 0.0001) , PPE (Dk@1MHz: 2.5; Df@1MHz: 0.0007), Cyanate Ester (Dk@1MHz: 2.8; Df@1MHz: 0.005), Epoxy (Dk@1MHz: 3.9; Df@1MHz: 0.025).
Reinforced Materials:?E-glass (Dk@1MHz: 6.6; Df@1MHz: 0.0012), D-glass (Dk@1MHz: 4.1; Df@1MHz: 0.0008), NE-glass (Dk@1MHz: 4.4; Df@1MHz: 0.0006), Aramid fiber (Dk@1MHz: 4.0; Df@1MHz: 0.02), PTFE fiber (Dk@1MHz: 2.1; Df@1MHz: 0.0001).
Note: Dk means Dielectric constant, and Df means: Dissipation factor. The Electrical performance difference of PCB material is mainly decided by the combination of resin system and Reinforcement material.
The Main Electrical Performance Properties of PCB Materials
There are many types of PCB materials according to the usage of different electronic products. Here are the main characteristic parameters of PCB materials:
Dk (Dielectric Constant)
The ratio of the capacitance obtained by filling the charging medium with the electrode with the specified shape to the capacitance when the same electrode is in a vacuum. The dielectric constant decides the electrical signal transmission speed in the medium. The lower the Dielectric Constant, the faster the signal transmission speed, so when your products need fast signal transmission speed, you can refer to the Dielectric Constant of the material such as Rogers PCB materials which have very low Dk usually.
The PCB material selection according to the Dielectric Constant will be:
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Df (Dissipation Factor)
Dissipation factor generally can be defined as Insulating material or Dielectric in the alternating electric field, because the hysteresis effect of dielectric conductance and dielectric polarization, make a certain phase difference between the current phasor and the voltage phasor flowing in the dielectric, that will form a certain phase angle, the tangent value of this phase angle are Dissipation factor, and energy loss caused by that called dielectric loss, it is the physical quantity characterizing the power loss ability of dielectric and the signal loss ability of insulating materials. Such as Rogers PCB materials which have very low Df usually.
Nonpolar molecule material like PTFE, will not be affected by electromagnetic field change, the loss is relatively small. Normally the higher the frequency, the losses are bigger.
CTE(Coefficient of Thermal Expansion)
Expansion and contraction phenomenon of objects due to temperature changes. Unit is: ppm/℃
Flame Retardant Grade
The grade of flame retardant characteristics can be divided into 94V-0, 94V-1, 94V-2, and 94-HB. The most commonly used material is RF4 material normally which meets the 94V-0 standard.
TG Value
TG is short for glass transition, it means the temperature of PCB substrates and PCB laminates melting from solid state to fluid, namely melting point.
The normal TG value is over 130°. High TG is normally over 170°. Medium TG is approximately greater than 150°. The higher the TG value, the better the heat resistance of the material.
If the working environment temperature term exceeds the TG value of the material, it will cause softening, deformation, melting, etc. and also there will be problems if there is a sharp decline in mechanical and electrical characteristics.
CTI(Comparative Tracking Index)
The maximum voltage value that the material surface withstands 50 drops of electrolyte without the formation of leakage traces. The unit is V. Normal FR-4 materials are around 175 V. But some materials can be 600V or more.
CAF (Conductive Anodic Filament)
It refers to applying DC voltage to the printed circuit board and placing it in a high-temperature and wet environment, with the positive voltage between lines or holes. The electrochemistry of an electrical short circuit can be caused by the conductive substance growing along the glass fiber from the pole side to the cathode side by the products of the corrosion process.
Usually, it radiates from the anode in the circuit and migrates towards the cathode along the interface surface between glass fiber and epoxy resin, forming conductive filaments.
Via spacing of different networks: it is positively correlated with CAF results, that is, the larger the spacing, the better the caf performance
RTI (Relative Thermal Index)
Through the accelerated aging test results of 6000 to 20000 hours, this index infers the maximum temperature that the material can withstand in 100000 hours, which is what we usually call the long-term use temperature of the plastic. RTI temperature also called UL temperature or electrical temperature is the long-term use temperature.