The material of high frequency PCB has a large influence on its electrical and mechanical properties, especially its thermal expansion coefficient, which can greatly affect the performance of electronic components and circuit boards. In this article we will focus on what things are considered while choosing the material of high frequency PCB.
Thermal conductivity is the ability of a material to conduct heat. High thermal conductivity means that the material can transfer heat more quickly, which is why we use copper and aluminum in many of our electronics, like laptops and cell phones. Thermal conductivity is measured in watts per meter Kelvin (W/mK).
The lower the thermal conductivity, the better. This is why we use copper and aluminum in many of our electronics. These materials have low thermal conductivity, which means that they can transfer heat more quickly.
The thermal conductivity of a material can be affected by how much of that material there is. For example, if you have two pieces of copper wire with the same thickness but different lengths, the one with the longer length will have a higher thermal conductivity.
Thermal expansion coefficient.
The thermal expansion coefficient is the ratio of the change in length to the initial length. Generally, materials with a low thermal expansion coefficient are desirable for use in high frequency applications.
The thermal expansion coefficient is a measure of how much a material expands or contracts when its temperature changes. Metals have a low thermal expansion coefficient, while ceramics and polymers have high thermal expansion coefficients. The difference in thermal expansion between metals and polymers can be significant enough to cause problems in many applications.
Dielectric constant is the measure of the ability of a material to store an electric field. The higher dielectric constant, better insulation properties. Dielectric constant is usually measured at 1 MHz.
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In addition to its role in insulating high-frequency signals, dielectric materials also affect signal quality by providing high capacitance or low dissipation factor (tanδ).
The capacitance is the ability of a material to store an electrical charge. The higher the capacitance, the better insulation properties. Dissipation factor (tanδ) is the measure of how much energy is lost in a capacitor when an AC current flows through it.
Insulation breakdown strength.
In order to ensure that the breakdown strength of high frequency PCB is greater than its maximum peak voltage, you must select a material with a high breakdown strength. The selection criteria include:
- Thickness of dielectric material and its dielectric breakdown strength;
- Maximum peak voltage applied across the insulation.
Material loss, dielectric loss tangent.
When choosing the material, you must consider the following parameters:
- Dielectric loss tangent. This is the most important parameter of high frequency PCB material. High loss tangent means that the dielectric loss will be large, which will lead to higher impedance and attenuation at high frequency signals. The value of this parameter is less than 1 if it does not have any dielectric losses and more than 1 if it has a lot of them;
- Material loss tangent. It indicates how much energy does not pass through the material (resists) when it flows through it after being reflected at its surface;
- Thermal conductivity and thermal expansion coefficient are also very important parameters because they affect heat transfer in electronic devices;
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The above are some of the parameters that you can pay attention to when choosing a PCB material. We have also introduced some commonly used materials for reference. The choice of material is very important after all, so we hope that this article can help you make more informed decisions in the future!