PCB Tech - FR4 board PCB multilayer board lamination process

The parameters such as the total thickness and number of layers of the PCB multi-layer laminate are limited by the characteristics of the PCB board. Special plates generally provide limited varieties of plates with different thicknesses, so the designer must consider the characteristics of the plate and the limitations of the PCB processing technology during the PCB design process.
Among them, FR4 boards have various thicknesses, and there are a wide range of boards suitable for multi-layer lamination. The following table takes FR4 board as an example to give a multilayer board laminate structure and board thickness distribution parameters for reference by PCB design engineers.

Performance comparison of main parameters of PCB board
The parameters that have the greatest impact on PCB design and processing are the dielectric constant and loss factor. For PCB multi-layer board design, the selection of the board also needs to consider processing punching and lamination performance.
Based on the above analysis of transmission line characteristic impedance, loss, propagation wavelength and sheet comparison, product design must consider cost and market factors.
Therefore, it is recommended that in the PCB design, the designer chooses the board to consider the following key factors:
(1) Different signal working frequency has different requirements for the plate.
(2) FR4 boards can be selected for PCBs that work below 1GHz, with low cost and mature multi-layer laminate technology. If the signal input and output impedance is low (50 ohms), the characteristic impedance of the transmission line and the coupling between the lines need to be strictly considered when wiring. Unstable.
(3) For optical fiber communication products above 622Mb/s and small-signal microwave transceivers above 1G and below 3GHz, modified epoxy resin materials such as S1139 can be used, because its dielectric constant is relatively stable and costly at 10GHz The process of low and multi-layer laminates is the same as FR4. Such as 622Mb/s data multiplexing and branching, clock extraction, small signal amplification, optical transceivers, etc. It is recommended to use this type of board to facilitate the production of multi-layer boards and the cost of the board is slightly higher than FR4 board (about 4 cents/cm2 higher) ), the disadvantage is that the thickness of the substrate is not as complete as FR4. Or, use RO4000 series such as RO4350, but the RO4350 double panel is generally used in China. The disadvantage is that the number of different thicknesses of these two plates is not complete, and it is not convenient to produce multi-layer printed boards due to the requirements of the thickness of the plates. For example, RO4350, sheet manufacturers produce four sheet thicknesses such as 10mil/20mil/30mil/60mil, and currently there are fewer domestic imports, which restricts laminate design.
(4) For large-signal microwave circuits below 3GHz, such as power amplifiers and low-noise amplifiers, it is recommended to use double-sided plates similar to RO4350. RO4350 has a fairly stable dielectric constant, low loss factor, good heat resistance, and processing technology comparable to FR4. The cost of the board is slightly higher than that of the FR4 board (about 6 minutes/cm2 high).
(5) Microwave circuits above 10GHz, such as power amplifiers, low-noise amplifiers, up-down converters, etc., have higher requirements for plates. It is recommended to use double-sided plates with performance equivalent to F4.
(6) The multi-layer PCB for wireless mobile phones requires dielectric constant stability, low loss factor, low cost, and high dielectric shielding requirements. It is recommended to use a plate with similar performance to PTFE (multi-purpose in the United States/Europe), or FR4 board Combine and bond with high-frequency boards to form low-cost, high-performance laminates.