Basic Requirements for HF Microwave Boards
A. Substrate Telecom engineers in the design, has been based on the actual impedance of the need to select the specified dielectric constant, dielectric thickness, copper foil thickness, therefore, in accepting the order, to carefully check, must meet the design requirements.
B. Transmission line production accuracy requirements High-frequency signal transmission, for the characteristic impedance of the printed wire requirements are very strict, that is, the production accuracy of the transmission line requirements are generally ± 0.02mm (± 0.01mm precision transmission line is also very common), the edge of the transmission line to be very neat, tiny burrs, notches are not allowed to produce.
C. Plating requirements for high-frequency microwave board transmission line characteristic impedance directly affects the transmission quality of microwave signals. The size of the characteristic impedance and the thickness of the copper foil has a certain relationship, especially for the hole metallization of the microwave plate, the thickness of the coating not only affects the total thickness of the copper foil, but also affects the precision of the wire after etching room engraving, so the size and uniformity of the thickness of the plating, to be strictly controlled.
D. Mechanical processing requirements first of all, high-frequency microwave board materials and printed boards of epoxy glass cloth material in the machining is very different, and secondly, high-frequency microwave boards are much higher than the requirements of the printed boards of the processing accuracy, the general shape of the tolerance of ± 0.1mm (high precision is generally ± 0.05mm or for the 0 ~ -0.1mm).
F. Characteristic impedance requirements The previous section has talked about the content of the characteristic impedance, which is the most basic requirements of the high-frequency microwave board, can not meet the requirements of the characteristic impedance, all in vain.
High-frequency microwave board production should pay attention to the issue of:
A. Processing of Engineering Data: CAM processing of customer documents, we must grasp the contents of two aspects, one is to carefully penetrate the production of transmission line accuracy requirements, and the second is based on the accuracy requirements and combined with the factory's process capabilities, to make appropriate process compensation.
B. Undercutting: Usually printed board undercutting are used shears or automatic openers, but for microwave media materials can not be generalized, according to different media characteristics, and choose a different undercutting method, more milling, cutting-based, so as not to affect the flatness of the material and the quality of the board.
C. Drilling: For different media materials, not only drilling parameters are different, and the top angle of the drill, edge length, helix angle, etc. have their special requirements, for aluminum-based, copper-based microwave media materials, drilling processing methods are different to avoid burrs.
D. Through-hole Grounding: In general, the through-hole grounding method using chemical precipitation of copper, chemical precipitation of copper is usually used in chemical or plasma processing, from the safety point of view, we use the plasma method, the effect is very good, and for the aluminum-based microwave dielectric materials, if the use of the usual chemical precipitation of copper, there is considerable difficulty, it is generally recommended to use the method of metal conductive material grounding hole filling is more appropriate, but the hole resistance is generally less than 20. But the hole resistance is generally less than 20.
E. Graphics Transfer: This process is to ensure the accuracy of the graphics of an important process. In the choice of photoresist, wet film, dry film and other photographic materials, must meet the requirements of the graphic accuracy, while photolithography or exposure machine light source must also meet the needs of the process.
F. Etching: This process should strictly control the etching process parameters, such as: the content of each component of the etching solution, etching solution temperature, etching speed. Ensure that the wire edge neat, no burrs, gaps, wire precision within the tolerance requirements. To do this practically, it is very necessary to make fine efforts.
G. Coating: High-frequency microwave board wire on the final coating generally have tin-lead alloy, tin-indium alloy, tin-strontium alloy, silver, gold and so on. But to electroplating pure gold is more common.
H. Forming: High-frequency microwave board molding and printed boards, the same as the main CNC milling. But the milling method for different materials, there is a big difference. The milling of metal-based microwave boards requires the use of neutral coolant for cooling, and the milling parameters are quite different.
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