High frequency boardPosted on 2020-02-18
The high frequency board refers to a high frequency circuit board. Special circuit boards with high electromagnetic frequencies, generally speaking, high-frequency boards can be defined as frequencies above 1GHz. The price is high, usually about 1.8 per square centimeter, about 18,000 yuan per square meter. The high-frequency board includes a core board provided with hollow grooves and a copper-clad board adhered to the upper surface and the lower surface of the core board by flow glue. The upper and lower opening edges of the hollow groove are provided with ribs.
Ｔable of Contents
Application field of high frequency board
High-frequency board selection
Basic characteristics of high-frequency board materials
FR4 circuit board plate, how to distinguish between ordinary board and high frequency board?
What happens when the high-frequency board has poor performance
High frequency board features
High-frequency board production requirements
1 Application field of high frequency board
High frequency and induction heating technology currently has the highest heating efficiency, fastest speed, and low energy consumption and environmental protection for metal materials. It has been widely used in various industries for metal materials in hot processing, heat treatment, hot assembly and welding, melting and other processes. It can not only heat the workpiece as a whole, but also localize the workpiece in a targeted manner; it can achieve deep heat penetration of the workpiece, and it can also heat only its surface and surface layer; The material is heated indirectly. and many more. Therefore, induction heating technology is bound to be more and more widely used in various industries. Its various physical properties, accuracy, and technical parameters are very high. It is often used in fields such as automobile anti-collision systems, satellite systems, and radio systems. High frequency of electronic equipment is a development trend.
2 High-frequency board selection
Made of high dielectric constant and low high frequency loss. The currently used high frequency board substrate is a fluorinated dielectric substrate, such as polytetrafluoroethylene (PTFE), which is usually called Teflon, and is usually applied above 5GHz. In addition, there are FR-4 or PPO substrates that can be used for products between 1GHz and 10GHz. The physical properties of these three types of high-frequency substrates are compared as follows.
The three types of high-frequency substrate materials used at the present stage are epoxy resin, PPO resin and fluorine resin.The cost of epoxy resin is the cheapest, while fluorine resin is the most expensive. Considering frequency characteristics, fluororesin is the best and epoxy resin is inferior. When the product application frequency is higher than 10GHz, only fluorine resin printed boards can be used. Obviously, the performance of the fluororesin high-frequency substrate is much higher than that of other substrates, but its disadvantages are poor rigidity and high thermal expansion coefficient in addition to high cost. For polytetrafluoroethylene (PTFE), in order to improve performance, a large number of inorganic substances (such as silica SiO2) or glass cloth are used as reinforcing filler materials to improve the rigidity of the substrate and reduce its thermal expansion. In addition, because the polytetrafluoroethylene resin itself is molecularly inert, it is not easy to have poor bonding with copper foil, so special surface treatment of the bonding surface with copper foil is even more needed. The treatment method includes chemical etching or plasma etching of the polytetrafluoroethylene surface, increasing the surface roughness, or adding an adhesive film layer between the copper foil and the polytetrafluoroethylene resin to improve the binding force, but it may have a dielectric property. Impact, the development of the entire fluorine-based high-frequency circuit substrate requires the cooperation of multiple parties such as raw material suppliers, research units, equipment suppliers, PCB manufacturers and communication product manufacturers to keep up with the rapid development of the field of high-frequency circuit boards. Need.
3 Basic characteristics of high-frequency substrate materials
(1) The dielectric constant (Dk) must be small and very stable. Generally, the smaller the better, the better the signal transmission rate is inversely proportional to the square root of the dielectric constant of the material. High dielectric constant is likely to cause signal transmission delay.
(2) The dielectric loss (Df) must be small, which mainly affects the quality of signal transmission. The smaller the dielectric loss, the smaller the signal loss.
(3) The thermal expansion coefficient should be consistent with the copper foil as much as possible, because the inconsistency will cause the copper foil to separate in the change of heat and cold.
(4) If the water absorption is low and the water absorption is high, it will affect the dielectric constant and dielectric loss when it is wet.
(5) Other heat resistance, chemical resistance, impact strength, peel strength, etc. must also be good.
4 FR4 circuit board material, how to distinguish between ordinary board and high frequency board?
Common board cotton fiber paper
High frequency board is usually pressed with FR4 glass fiber board, and it is pressed with a whole epoxy glass cloth. The color is more uniform and bright. The density is greater than the low frequency board, which is the weight point.
Many low-frequency boards are laminated with low-end materials, such as: paper substrate, composite substrate, epoxy board (also called 3240 epoxy board, phenolic board), FR-4 glass fiber board (plywood), paper substrate And composite substrate, the overall density should be low, the back color is consistent, but it is easy to see that there is basically no fiberglass cloth pattern inside the substrate. The difference between epoxy board and FR4 glass fiber composite board is that the color of the back substrate is different. The epoxy board is at the fracture, and it is easy to see a white powder with a hand or other tools. The color is off-white. of. The FR4 composite board is easier to see, because it is pressed with the scraps of FR4 fiberglass cloth, and a large strip can be seen on the back of the entire board.
5 What will happen when the high-frequency board has poor performance?
The poor performance of the high-frequency board is mainly due to the low dielectric constant value affecting the stability of the high-frequency circuit. High frequency has a skin effect, and the low dielectric constant of the circuit board causes leakage of high frequency components, which should result in signal attenuation, frequency offset drift, and severe vibration stoppage. The overall electrical performance index is reduced.
6 High frequency board features
The high-frequency circuit board provided by the utility model is provided with ribs at the upper and lower opening edges of the hollow groove of the core board, which can block the flow of glue. In this way, the core board and the cover placed on the upper and lower surfaces of the core board When the copper plate is bonded, the flow glue will not enter the hollow groove, that is, the bonding operation can be completed with one pressing. Compared with the high-frequency circuit board which can be completed through secondary pressing in the prior art, the high-frequency circuit in the utility model The plate structure is simple, the cost is low, and it is easy to manufacture.
7 HF board production requirements
The high frequency board is one of the difficult boards, so it must meet the production requirements as much as possible.
1. The drilling speed should be 180 / S. A new drill bit should be used, and aluminum pads should be used. It is best to drill with a single PNL. There should be no water in the hole.
2. Overhole refining agent PTH hole Sample can use concentrated sulfuric acid (preferably not used) 30Min
3, Grinding plate and copper wire
4, special attention: high frequency board does not need to remove rubber residue.
1. If the high-frequency board needs green oil to be grounded, it is not allowed to grind the board before soldering, and the red stamp is stamped in MI.
2. If the high-frequency board needs green oil to be printed on the substrate, the green oil should be printed twice (to prevent the green oil from blistering on the substrate). The plate should not be ground before etching and tin removal. It can only be air-dried. For the first time, use the 43T screen to print the segmented baking sheet normally: 50 degrees 50Min 75 degrees 50Min 95 degrees 50Min 120 degrees 50Min 135 degrees 50Min 150 50Min degrees. Expose with the film on the line. The plate can be ground after development. Second Normal production. Need to note in MI: the first time the bottom line with line film alignment.
3． If high-frequency board needs green oil to be printed on some substrates and green oil is not printed on some substrates, a “priming film” is required. The bottom film only retains green oil on the substrate. Normal production. The picture below is a special “priming film” for 018212.
Special attention should be paid to the printing of green oil on substrates like 018092, which can only be printed once (see the figure below, the blue part is the green oil window), to prevent the green oil from developing on the substrate after the first green oil is used .
Add 150 degrees and 30 minutes before spraying tin before spraying tin.
Unrequired line width tolerance is ± 0.05mm. It can be produced according to customer requirements.
Use specified plate See requirements. Because the plate price is more expensive, only 1PNL can be opened.