FR4 circuit board multilayer board lamination process
The parameters such as the total thickness and number of layers of the PCB laminate are limited by the characteristics of the PCB. Special plates generally have a limited variety of plates of different thicknesses, so designers must consider the plate characteristics and PCB processing limitations in the PCB design process.
Among them, FR4 sheets are available in various thicknesses and are suitable for a wide range of laminated sheets. The FR4 sheet is taken as an example to give a multilayer laminate structure and sheet thickness distribution parameters for PCB design engineers.
Comparison of main parameters of PCB sheet
The most influential parameters of the board material for PCB design and processing are dielectric constant and loss factor. For PCB multi-layer board design, the board selection also needs to consider punching and lamination performance.
From the above transmission line characteristic impedance, loss, propagation wavelength analysis and sheet comparison, product design must consider cost and market factors.
Therefore, it is recommended that in the PCB design, the designer selects the board to consider the following key factors:
(1) Different signal operating frequencies have different requirements on the board.
(2) FR4 board can be selected for PCBs working below 1 GHz, and the cost is low, and the multi-layer press board is mature. If the signal input and output impedance is low (50 ohms), the transmission line characteristic impedance and the line-to-line coupling need to be strictly considered during wiring. The disadvantage is that different manufacturers and different batches of FR4 plates are doped differently, and the dielectric constant is different (4.2-5.4). Unstable.
(3) Optical fiber communication products operating above 622 Mb/s and small signal microwave transceivers above 1G and below 3 GHz can be modified epoxy resin materials such as S1139, because the dielectric constant is stable at 10 GHz and the cost is relatively high. The low-layer, multi-layer press process is the same as the FR4. Such as 622Mb / s data multiplexing shunt, clock extraction, small signal amplification, optical transceivers, etc. is recommended to use such panels, in order to make multi-layer board and the board cost is slightly higher than FR4 board (high 4 points / cm2 or so The disadvantage is that the thickness of the substrate is not as complete as the FR4. Or, use RO4000 series such as RO4350, but currently China generally uses RO4350 double panel. The disadvantage is that the number of different plate thicknesses of the two kinds of plates is not complete, and it is not convenient to make multi-layer printed boards due to the thickness requirements of the plates. For example, RO4350, the plate manufacturer produces four thicknesses of 10mil/20mil/30mil/60mil, and currently there are fewer imported varieties in China, thus limiting the laminate design.
(4) Large-signal microwave circuits below 3 GHz, such as power amplifiers and low-noise amplifiers, are recommended to use double-sided plates similar to RO4350. The dielectric constant of RO4350 is quite stable, the loss factor is low, the heat resistance is good, and the processing technology is equivalent to FR4. The cost of the board is slightly higher than that of the FR4 board (about 6 points/cm2).
(5) Microwave circuits above 10 GHz, such as power amplifiers, low noise amplifiers, up and down inverters, etc., require higher sheet metal. It is recommended to use double-sided sheets with the same performance as FR4.
(6) Wireless mobile phone multi-layer PCB board requires sheet dielectric constant stability, low loss factor, low cost, and high dielectric shielding requirements. It is recommended to use a sheet similar to PTFE (US/Europe, etc.) or FR4 board. Combined with high frequency board to form a low cost, high performance laminate.
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