In recent years, many printed board companies in East China like , North China, and the Pearl River Delta are staring at the market of high-frequency microwave boards ( Like Rayming Technology is one of HDI PCB manufacturer ), collecting the dynamics and information of high-frequency waves and Teflon (PTFE). The new varieties of the board are regarded as an indispensable accessory product for the electronic information high-tech industry, and research and development are strengthened. Some company CEOs have identified high-frequency microwave boards as a new economic growth point for future enterprises.
Foreign experts predict that the market development of high-frequency microwave boards will be very fast. In the fields of communications, medical, military, automotive, computer, instrumentation, etc., the demand for high-frequency microwave boards is rapidly rising. A few years later, high-frequency microwave boards may account for about 15% of the total global printed boards. Taiwan, South Korea, Europe, the United States, and Japan have developed plans for this direction.
Ou Mei high-frequency microwave sheet suppliers Rogers, Arlon, Taconic, Metclad, GIL Japan Chukoh began to enter the potential big market in China in the past two years, looking for agents and teaching related technologies. GIL of the United States held a lecture on “Application and Manufacturing Technology of High-frequency Microwave Printed Boards” in Shenzhen. Hundreds of seats were full, and the corridors were full of corporate representatives to listen to the speech. Many of the CEOs listened to the whole. Day of technical lectures. I really didn’t expect domestic counterparts to have such a strong interest in high frequency boards. European and American sheet suppliers have been able to offer more than 100 varieties of sheet metal with dielectric constants from 2.10, 2.15, 2.17, … up to 4.5 or even higher.
In the Pearl River Delta and the Yangtze River Delta, it is understood that many companies have advertised orders for Teflon and high-frequency boards. It is said that some enterprises have reached the level of several thousand square meters per month. Many domestic radar and communication research institutes have increased the demand for high-frequency microwave sheets. Domestic high-frequency microwave printed boards, such as Huawei, Bell, and Wuhan Institute of Posts, are increasing year by year. Foreign companies engaged in high-frequency microwave products have also moved to China to purchase high-frequency microwave printed boards.
There are indications that high-frequency microwave panels are heating up in China.
(What is high frequency? 300MHZ or more, that is, the short-wave frequency range of wavelength 1m or more, generally called high frequency.)
- Why is it popular?
There are three reasons.
(1) Some of the frequency bands of high-frequency communications originally used for military purposes were made available to civilians (beginning in 1996), and civilian high-frequency communications were greatly developed. In the long-distance high communication, navigation, medical, transportation, transportation, warehousing and other fields to show their talents.
(2) High confidentiality and high transmission quality, which enable mobile phones, car phones, and wireless communications to develop at high frequencies, high picture quality, and broadcast and television broadcasts, using VHF and UHF broadcast programs. High information transmission requires satellite communication, microwave communication and optical fiber communication must be high frequency.
(3) The processing power of computer technology increases, the information memory capacity increases, and the signal transmission speed is urgently required.
In short, high-frequency and high-speed electronic information products place high demands on the high-frequency characteristics of printed boards.
- Why do you require a low ε (Dk) printed board?
ε or Dk, called the dielectric constant, is the ratio of the capacitance of a certain substance between electrodes to the capacitance of a vacuum capacitor of the same construction. Usually indicates the size of a material’s ability to store electrical energy. When ε is large, the ability to store electrical energy is large, and the electrical signal transmission speed in the circuit becomes low. The direction of the current through the printed circuit board is usually positive and negative alternately, which is equivalent to the process of continuously charging and discharging the substrate. In the exchange, the capacitance affects the transmission speed. This effect is even more important in high-speed transmission devices. Low ε means that the storage capacity is small, and the charging and discharging processes are fast, so that the transmission speed is also fast. Therefore, in high frequency transmission, the dielectric constant is required to be low.
Another concept is dielectric loss. The energy consumed by the dielectric material under the action of an alternating electric field is called dielectric loss, and is usually expressed by the dielectric loss factor tan δ. ε and tan δ are directly proportional, and the high-frequency circuit also requires ε to be low, and the dielectric loss tan δ is small, so that the energy loss is also small.
- PTFE of Teflon printed board
In the printed board substrate, the dielectric constant ε of the polytetrafluoroethylene material is the lowest, typically only 2.6~2.7, while the dielectric constant ε of the FR4 of the general glass cloth epoxy substrate is 4.6~5.0. Therefore, the signal transmission speed of the Teflon printed board is much faster (about 40%) than the FR4. The Teflon plate has a loss factor of 0.002, which is 10 times lower than FR4’s 0.02, and the energy loss is much smaller. In addition, PTFE is called “Plastic King”, which has excellent electrical insulation properties, good chemical stability and thermal stability (so far there is no solvent that can dissolve it below 300 °C), so high frequency and high speed Signal transmission requires Teflon or other substrates with low dielectric constants. I have seen that Polyflon, Rogers, Taconic, Arlon, and Meclad can provide substrates with dielectric constants of 2.10, 2.15, 2.17, and 2.20, and the dielectric loss factor is 0.0005 to 0.0009 at 10 GHz. Polytetrafluoroethylene materials perform very well, but the process of processing them into printed boards has a completely different process than the traditional FR4, which is discussed later.
In the past two years, in practice, in addition to the requirement ε of 2.15 and 2.6, Rogers RO4000 and GIL1000 series such as ε3.38, 3.0, 3.2, and 3.8 are often used.
- Basic requirements for high frequency microwave boards
Due to the high frequency signal transmission, the characteristic impedance of the finished printed circuit board conductor is required to be strict, and the line width of the board is usually required to be ± 0.02 mm (the most stringent is ± 0.015 mm). Therefore, the etching process needs to be strictly controlled, and the negative film for photoimage transfer needs to be compensated according to the line width and the thickness of the copper foil.
- This type of printed circuit board transmits not the current, but the high-frequency electrical pulse signal. Defects such as pits, notches, pinholes, etc. on the wire can affect the transmission. Any such small defects are not allowed. Sometimes, the thickness of the solder mask is also strictly controlled. If the solder resist is too thick on the line and is too thin, it will be judged as unqualified.
- Thermal shock 288 ° C, 10 seconds, 1~3 times, no hole wall separation. For the Teflon plate, to solve the wettability in the hole, there is no hole in the chemical copper hole, and the copper layer plated in the hole can withstand thermal shock, which is a difficulty in making the Teflon plate. one. Because of this, many substrate manufacturers have developed a higher ε, and the chemical copper-plating process is the same as the conventional FR4 alternative, Rogers Ro4003 (ε3.38) and LGC-046 of Xi’an 704 (ε3.2±0.1). ) is such a product.
- Warpage: 0.5~0.7% of the finished board is usually required.
- Difficulties in processing high frequency microwave plates
Based on the physical and chemical properties of the polytetrafluoroethylene sheet, the processing technology is different from the traditional FR4 process. If the conventional epoxy resin glass fiber clad laminate is processed under the same conditions, a qualified product cannot be obtained.
(1) Drilling: The substrate is soft, and the number of holes in the drilling stack is small. Generally, the thickness of the 0.8 mm plate is preferably two stacks; the rotation speed is slower; the new drill bit is used, and the top angle and the thread angle of the drill bit have special request.
(2) Print-resistance soldering: After the board is etched, it is not possible to use a roller to polish the board before the solder resist green oil is applied to avoid damage to the substrate. Chemical methods are recommended for surface treatment. To do this: do not grind the board, after the solder mask is printed, the line and the copper surface are uniform, and there is no oxide layer, which is not easy.
(3) Hot air leveling: Based on the intrinsic properties of fluororesin, the sheet should be avoided as quickly as possible. Before spraying tin, it should be 150 °C, pre-heat treatment for about 30 minutes, and then spray tin immediately. The temperature of the tin bath should not exceed 245 ° C, otherwise the adhesion of the isolated pad will be affected.
(4) Milling shape: fluororesin is soft, ordinary milling cutter has a lot of burrs in shape and unevenness, and it needs to be milled with a suitable special milling cutter.
(5) Transportation between processes: It can’t be placed vertically, and it can only be placed in the basket. The whole process must not touch the circuit pattern inside the board with fingers. The whole process prevents scratches and scratches, scratches on the line, pinholes, indentations, and pits all affect signal transmission, and the board will reject it.
(6) Etching: Strictly control side etching, sawtooth, and notch, and the line width tolerance is strictly controlled ±0.02mm. Check with a 100x magnifying glass.
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