How to select material for High frequency and high speed PCB board?
When selecting PCB substrates for high frequency circuits, the variation characteristics of material DK at different frequencies should be specially studied. For requirements that focus on high-speed signal transmission or characteristic impedance control, focus on DF and its performance under frequency, temperature and humidity conditions.
In the case of frequency variation, the DK and DF values of general substrate materials vary greatly. Especially in the frequency range of 1MHz to 1ghz, their DK and DF values vary more significantly. For example, the DK value of ordinary epoxy glass fiber cloth base material (ordinary FR-4) is 4.7 at LMHZ frequency, while the DK value becomes 4.19 at LGHZ frequency. Above LGHZ, DK value changes gently. The variation tendency is to decrease with the increase of frequency (but the variation range is small). For example, at L0ghz, the DK value of FR-4 is typically 4.15. For substrate materials with high speed and high frequency characteristics, DK values vary little with frequency. At varying frequencies from LMHZ to LGHZ, DK remains in the 0.02 range. DK values tend to decrease slightly at different frequencies from low to high.
Under the influence of frequency variation (especially in the high frequency range), the dielectric loss factor (DF) of general substrate materials changes more than DK. The pattern of change tends to increase. Therefore, when evaluating the high frequency characteristics of substrate materials, the research focus is on the change of DF value. For substrate materials with high speed and high frequency characteristics, generally there are two distinct types of substrate materials in terms of high frequency variation characteristics: one is that its (DF) value changes very little with frequency. Another reason is that, although the range of variation is similar to that of general substrate materials, its (DF) value is lower.
The above is about the high frequency and high speed PCB board material knowledge from Runtek! Hope to help you!
