In recent years, the hottest products in the PCB industry are HDI PCB and Build-up Multilayer Board. However, in this high-tech development trend, there is another branch, the high-frequency PCB (Microwave Board).
What is the high-frequency circuit?
300MHZ or more, that is, the short-wave frequency range with a wavelength of 1 meter or more, which is generally called high frequency. Therefore, the circuitry that is applied for this signal range is the high-frequency circuit.
High-Frequency PCB is Getting Hot in China
Recently in China, many PCB manufacturers are staring at the market of high-frequency PCB, collecting new developments and information of high-frequency circuit applications, Teflon (PTFE) materials, and regard such circuit boards as the indispensable accessory products for the high-end electronic information industry. Some top management has identified high-frequency PCBs as a new economic growth point for the enterprises in the future.
Experts predict that the market development of high-frequency PCB will be very fast. In the fields of communications, medical, military, automotive, computer, instrumentation, etc., the demand for high-frequency PCB is rapidly rising. It is expected that after several years, high-frequency PCBs may account for about 15% of the total global printed circuit boards. Many PCB companies in Taiwan, South Korea, Europe, the United States, and Japan have formulated plans for development in this direction.
European and American high-frequency CCL (Copper-clad Laminates) suppliers Rogers, Taconic, and other companies have also entered the potential big market in China, looking for agents and spreading related technologies. GIL Company of the United States held a lecture on “Application and Manufacturing Technology of High-Frequency PCB” in Shenzhen, at which hundreds of seats were all full, and the corridors were full of corporate representatives to listen to the speech.
European and American CCL suppliers have been able to offer more than 100 varieties of CCLs with dielectric constants from 2.10, 2.15, 2.17, … up to 4.5 or even higher.
Many Chinese companies said are able to produce Teflon high-frequency PCBs in batches. It is said that some enterprises’ capacities have reached the level of thousands square meters per month. Many Chinese radar and communication research institutes increase the demands for high-frequency PCBs year by year, so do some leader communication companies such as Huawei and Bell. Some foreign companies engaged in high-frequency products also moved to China, for purchasing the high-frequency PCB easily.
These indications mean that high-frequency PCB is getting hot in China.
Why High-Frequency PCB Grows So Rapidly in China?
- Some frequency bands of high-frequency communications originally used for military purposes were given to civilian use (beginning in 1996), which greatly improved the civilian high-frequency communication.
- High-frequency PCBs enable mobile phones, car phones, wireless communications with high confidentiality and high transmission quality, enable broadcast and television transmission with high picture quality. High volume information transmission requires that satellite communication, microwave communication and optical fiber communication must be equipped with high-frequency PCBs.
- The increased processing power of computer technology and increased storage capacity require a higher speed of signal transmission urgently. In short, high-frequency and high-speed communication products have come up with high demands on the high-frequency characteristics of PCB.
Why is High-frequency Circuit With a Low ε (Dk) Required?
ε represents the dielectric constant, which is the ratio of certain capacitance’ capacity to the capacitance of a vacuum capacitor of the same structure, which generally indicates the ability of a material to store electrical energy.
When ε is high, the ability to store electrical energy is strong, which prolongs the process of charging and discharging the board, while reduces the signal transmission speed. Low ε means that the storage capacity is small, and the charging and discharging processes are fast so that the transmission speed is accelerated.
Another concept is dielectric loss (tan δ), which is the energy consumed by the dielectric material under the action of an alternating electric field. ε and tan δ are a positive correlation.
High-frequency circuit often requires low ε, meanwhile, a low tan δ.
Commonly Used High-frequency CCL Are Rogers, FR4, and Teflon.
- Rogers: It seems to be often recommended. There are many types, the prices of most of which are acceptable, ε and tan δ are relatively low, suitable for PCB prototyping.
- FR4: Theoretically applicable in applications requiring frequencies from 1 GHz to 10 GHz, but common FR4 have their own shortcomings and limitations. Nowadays the FR4 which is used to make high-frequency PCB is usually a special modified material.
- Teflon (PTFE): Another common material with a frequency of 5 GHz. Teflon is the best in terms of DK, loss and water absorption, usually more expensive than FR4 and Rogers. If your project requires frequencies above 10 GHz and high quality and stable signals, Teflon is the best one.
PS Electronics provides prototyping and small batch production based on top-level Rogers, FR4, and Teflon materials, refer to another article to see their specifications.What kinds of copper-clad laminates are available?
Basic Requirements for High-frequency PCB
High-frequency signal transmission requires strict impedance control, and the trace width tolerance of high-frequency PCB usually requires ±0.02mm (or ±0.015mm). Therefore, the PCB etching process needs to be strictly controlled, and the compensation is usually based on the line width and the thickness of the copper foil.
The trace of the high-frequency PCB transmit not the current, but the high-frequency electric pulse signals. Defects such as pits, notches, pinholes, etc. on the wires may affect the transmission, and any such small defects are not allowed.
Sometimes, the thickness of the solder mask is also required to be strictly controlled. If the solder resist is too thick or thin, the board will be judged to be unqualified. In addition, the warpage of the finished high-frequency PCB is usually limited within 0.5 to 0.7%.
What’s the Application of High-frequency PCB?
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, etc.
High-frequency PCBs are needed in communication and computer fields such as high-frequency communication, high-speed transmission, high confidentiality, high transmission quality, and high memory capacity processing.
High-frequency PCB is a new variety of high-tech PCBs, with the continuous development of high-speed and high-speed communication and computers, the future use of high-frequency PCB will certainly become wider and wider.