High frequency concept
High frequency PCB refers to high frequency circuit board. At present, high frequency and induction heating technology has the highest heating efficiency, the fastest speed, low consumption and environmental protection. It has been widely used in hot processing, heat treatment, hot assembly, welding, smelting and other processes of metal materials in all walks of life. It can not only heat the workpiece as a whole, but also heat the workpiece locally; It can realize the deep heat penetration of the workpiece, or only the surface and surface can be heated centrally; It can not only directly heat metal materials, but also indirectly heat non-metallic materials. wait. Therefore, induction heating technology will be more and more widely used in all walks of life.
Manufacturing requirements of high frequency board
High frequency PCB board is one of the most difficult boards, so it must meet the manufacturing requirements as much as possible.
1. The drilling feed speed should be slow, 180 / s. A new drill nozzle should be used, and aluminum sheets should be placed on the top and bottom. It is best to drill with a single PNL, and no water can be encountered in the hole
2. Concentrated sulfuric acid (preferably not used) can be used for PTH pore template of pore finishing agent for 30min
3. The grinding plate copper sinking line is made as normal double-sided
4. Special attention: the high-frequency board does not need to remove the glue residue.
2、 Anti welding
1. If the high-frequency plate needs green oil backing, it is not allowed to grind the plate before resistance welding, and a red seal shall be stamped in MI.
2. If the high-frequency board needs to be printed with green oil on the substrate, it shall be printed with green oil twice (to prevent green oil foaming on the substrate). The Board shall not be ground before etching and tin withdrawal, but can only be air dried. For the first time, the 43T screen plate shall be used for normal printing of segmented baking plate: 50 ° 50min, 75 ° 50min, 95 ° 50min, 120 ° 50min, 135 ° 50min, 150 50min. The plate shall be exposed with line film, grinded after development, and made normally for the second time. Note in MI: line film alignment is used for the first priming.
3. If the high-frequency board needs to be printed with green oil on some substrates and not on some substrates, it needs to produce a "backing film". The backing film only retains the green oil on the substrate, and the second normal production can be carried out after the backing baking board. The following picture shows the need of 018212, especially the "backing film".
Special attention should be paid to printing green oil only once if it is not printed on the substrate like 018092 (see the figure below, the blue part is the green oil window), so as to prevent the green oil on the substrate from developing after the first green oil priming.
3、 Tin spraying
Before tin spraying, bake 150 degrees for 30 minutes before tin spraying
4、 Line tolerance
The line width tolerance without requirements shall be ± 0.05mm. If required, it shall be made according to the customer's requirements.
To use the specified plate, see requirements. Because the plate price is expensive, only 1pnl can be opened.
High frequency PCB material selection
In recent years, the continuous introduction of wireless communication, optical fiber communication and high-speed data network products, high-speed information processing and wireless analog front-end modularization have put forward new requirements for digital signal processing technology, IC process and Microwave PCB design, as well as higher requirements for PCB plate and PCB process. For example, commercial wireless communication requires the use of low-cost plates and stable dielectric constant（ ε R variation error is between ± 1-2%), low dielectric loss (below 0.005). Specific to the PCB board of mobile phone, it also needs to have the characteristics of multi-layer lamination, simple PCB processing technology, high reliability of finished board, small volume, high integration and low cost. In order to challenge the increasingly fierce market competition, electronic engineers must make a compromise between material performance, cost, difficulty of processing technology and reliability of finished boards. At present, there are many plates available for selection, and the representative commonly used plates are: epoxy resin glass cloth laminate FR4, polyester fluoroethylene PTFE, polytetrafluoroethylene glass cloth F4, modified epoxy resin FR4, etc. Special plates, such as sapphire substrate and ceramic substrate used in satellite microwave transceiver circuit; Microwave circuit substrate GX series, ro3000 series, ro4000 series, TL series, TP-1 / 2 series, f4b-1 / 2 series. They are used on different occasions, such as FR4 for mixed signal circuits below 1GHz, polyvinylidene fluoride PTFE for multi-layer high-frequency circuit boards, Teflon glass cloth fiber F4 for double-sided microwave circuit boards, and modified epoxy resin FR4 for high-frequency heads of household appliances (below 500MHz). FR4 plate is widely used because of its easy processing, low cost and easy lamination. Next, we analyze the characteristics of microstrip transmission line, multilayer plate lamination process, plate parameter performance comparison and other aspects, give the selection scheme of PCB plate for special applications, and summarize the key points of high-frequency signal PCB design for the reference of electronic engineers.