I PCB High Frequency Board Definition
High-frequency board refers to a special circuit board with high electromagnetic frequency. It is used in the fields of high frequency (frequency greater than 300 MHZ or wavelength less than 1 m) and microwave (frequency greater than 3 GHz or wavelength less than 0.1 m). This kind of circuit board is produced on the basis of of microwave copper clad by a part of process method used in a common rigid wiring board manufacturing or a special processing method. In general, a high frequency board can be defined as a circuit board is with a frequency above 1 GHz.
With the rapid development of science and technology, more and more equipment designs are applied in the microwave frequency band (>1GHZ) or even in the millimeter wave field (30GHZ), which means that the frequency is getting higher and higher, so are the requirements of base material of circuit board.
For example, the substrate material needs to have excellent electrical properties, good chemical stability, and have very small loss as the frequency of the power signal increases, so the importance of the high frequency material is highlighted.
II PCB High Frequency Material Classification
- Powder Ceramic Filled Thermoset Material
- PTFE (Teflon) Material
III High Frequency High Speed Material
When selecting material for high-frequency PCB, special consideration should be given to the variation of material DK under different frequencies. While for requirements like emphasis on signal high-speed transmission and impedance control, we need to focus on DF and its performance under frequency, temperature and humidity conditions.
Under the condition of frequency change, the general type substrate material shows a larger change of DK and DF values. Especially for frequency from l MHz to l GHz, their DK and DF values change more evidently. Above l GHz, its DK value tends to be less flexible. Its trend is to become smaller(but not much) as the frequency increases. The high-speed and high-frequency material has a small change in the DK value in the case of a frequency change, and the DK maintains a variation in the range of 0.02 from 1 MHz to 1 GHz. Its DK value tends to decrease slightly from low to high frequency.
For a general type substrate material, it DF(The dielectric loss factor) value is larger than that of DK when affected by frequency change(especially in a high frequency range).The law of change tends to increase. Therefore, when evaluating the high-frequency characteristics of a substrate material, we should focus on the change of its DF value.
IV How to Choose High Frequency High Speed Material
Choosing PCB material needs to consider these factors: meeting design requirements, mass production, and cost. To put it in a simple way, design requires both electrical and structural reliability. It is far more important when designing high speed PCB boards (greater than GHz).
The main considerations of choosing the right pcb material are as follows:
For example, press-fitting properties, temperature performance, etc., CAF/heat resistance and mechanical toughness (stickiness) (good reliability), fire rating;
- Various properties matching the product (electricity, performance stability, etc.):
Low loss, stable Dk/Df parameters, low dispersion, small variation coefficient with frequency and environment, small tolerance of material thickness and glue content (good impedance control), if the trace is long, consider low roughness copper foil.
- The availability of materials:
Many high-frequency material’s procurement cycles are very long, even for 2-3 months; in addition to the conventional high-frequency material such as RO4350, RO4003 in stock, many high-frequency materials may need to be ordered. Therefore, good communication with manufacturers and preparing materials in advance is also important.
Consider the price sensitivity of products, whether it is consumer products, or products in communications, medical, industrial, military applications;
Among all the above factors, the running speed of high-speed digital circuits is the main factor for PCB selection. The higher the speed of the circuit, the smaller the Df value of the selected PCB should be.
From the material Df:
Df between 0.01～0.005 pcb material suitable for upper limit 10Gb/S digital circuits;
Df is between 0.005～0.003 pcb material suitable for upper limit 25Gb/S digital circuits;
Df no more than 0.0015 pcb material suitable for 50Gb/S or even higher speed digital circuits.
Commonly Used High Speed Material:
1) Rogers: RO4003, RO3003, RO4350, RO5880, RO3000 series, RT series, TMM series etc.
2) Arlon’s AD/AR series
3) Taconic’s RF Series, TLX Series, TLY Series
4) TaiYao TUC: Tuc862, 872SLK, 883, 933, etc.
5) Panasonic: Megtron4, Megtron6, etc.
6) Isola: FR408HR, IS620, IS680, etc.
7) Nelco: N4000-13, N4000-13EPSI, etc.
8) Dongguan Shengyi, Taizhou Wangling, Taixing microwave F4B, F4BM, F4BK, TP-2, etc.
V Where is High Frequency Microwave Board Used?
High-frequency microwave printed boards are required in communication and computer fields such as high-frequency communication, high-speed transmission, high confidentiality, high transmission quality, and high memory capacity processing.
Satellite receivers, base antennas, microwave transmissions, car phones, global positioning systems, satellite communications, communication equipment adapters, receivers, signal oscillators, home appliance networking, high-speed computers, oscilloscopes, IC test instruments, mobile communication products, power amplifiers, low-noise amplifiers, etc.; passive components such as power splitters, couplers, duplexers, filters; automotive anti-collision systems, satellite systems, radio systems, etc.