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Why is the material of PCB board so important?

Author:pbmo.cn Addtime:2022-09-30 17:19:12 Click:281

In the past, the wiring of a circuit was direct current in nature and the surrounding environment was not very important, but now it is necessary to control an electromagnetic field. The electromagnetic field is capacitive and the wire is close to its return path (high capacitance). It is also a magnetic field and is inductive. This is how the signal propagates along the loop (low inductance). And manage the EM field, not just go through the line connecting the two points, the field does not exist in inline, but exists between linear and its return path, return path is usually a GND layer ACTS as a reference point, as a result, the energy exists in medium between the two materials, so the parameters of the PCB circuit board material is also part of the circuit performance.

The electrical properties of the material are measured by the dielectric constant (Dk), expressed as εr. Permittivity represents the ability of energy to travel through a material at different frequencies and can also be measured by the loss factor (Df), also known as the tangent of the loss Angle, which measures how much energy is dissipated or lost in the material. The energy field will propagate through the medium material. Materials resist the flow of energy, and each material has a known measurement. The permittivity εr of air is 1, and the average permittivity εr of FR-4 materials is about 4. Faster circuits require small impedance and low energy loss, so the permittivity εr range of high-speed materials can be as low as 3.

As circuits get faster and faster, most people equate the speed to the frequency of the circuit, but it must be understood that the energy delivered by each pulse measured during the rise time (Tr) is voltage and frequency dependent, that is, this energy determines the energy field of the signal as it transitions from zero to its voltage. In order to control this energy field, it is necessary to understand that material selection is an integral part of circuit function. Engineers and designers have to take these factors into account from day one.

Materials play an important role, but designers must ensure that signal integrity issues do not arise due to violations of signal return paths, impedance matching, or signal crosstalk. Another factor to consider in electronics is the consistency of the fabric pattern. Because the DKS between braided fabrics and resins differ, they use a material called spread braided fabrics. They spread the fabric out to form a consistent DKS, which is essential for differential wiring performance.