First, the radio frequency plate laminated structure
In addition to the impedance of the RF PCB single, the laminate of the RF PCB is also required to consider problems such as heat dissipation, current, devices, EMC, structures, and skin effects, usually we are layered and stacked in multi-layer printed plates. Comply with some basic principles:
A) Each layer of the RF PCB is largely paved. There is no power supply plane, and the upper and lower layers of the RF wiring layer should be grounded. Even the digital portion can exist in the power supply plane, but the RF zone still needs to meet the requirements of each floor.
B) For RF double panels, the top layer is a signal layer, and the bottom layer is ground plane. The four-layer RF veneer, the top layer is the signal layer, the second layer, and the fourth layer are ground planes, the third layer takes power, and the control line. Special circumstances can take some RF signal lines in the third layer. More layers of RF single boards are pushed.
C) For RF backplanes, both the upper and lower surface layers are ground, in order to reduce the impedance discontinuities of the via and the connector, the second, third, four, and five layers take the digital signal. And other strip lines from the bottom are RF signal layers. Similarly, the RF signal layer is adjacent to two adjacent two layers, and each layer should be paved.
D) For large power, the RF board of the large current should place the RF main link to the top layer and connected with a wide microstrip line. This facilitates heat dissipation and reduces energy loss, and reduces wire corrosion errors.
E) The power supply plane of the digital portion should be close to the ground plane and arrange it under the ground plane. This can utilize the capacitance between the two metal plates as a smooth capacitor of the power supply, and the ground plane also plays a shielding effect on the radiation current distributed on the power supply plane. The specific lamination method and the plane segmentation requirement can refer to the "20050818 Printed Circuit Board Design Specification - EMC Requirements" promulgated by the EDA design department, and is subject to the latest standards.
Second, RF board wiring requirements
Corner
If the RF signal trace is at right angle, the effective line width at the corner will increase, and the impedance is discontinuous. Therefore, it is necessary to process the corner, mainly two methods of cut angles and fillets.
(1) The cut angle is suitable for a relatively small corner. As shown in Figure left, the adopted frequency of the cut angle can reach 10 GHz.
(2) The radius of the arc angle should be large enough, in general, to ensure: R>3W. Figure right
2. Microerer wiring
The top layer of the PCB radio frequency signal, the plane layer under the radio frequency signal must be a complete ground plane to form a microstrip line structure. To ensure the structure integrity of the microstrip line, there is the following requirements:
(1) The edges of the microstrip line are at least 3 W width from the edge of the plane below. And in the 3W range, there is no non-ground via.
(2) The microstrip line to the shield wall should be maintained at 2W or more. (Note: W is a line width).
(3) The non-coupling microstrip line in the same level should be treated with a packed copper-proof and add aperture on the ground copper, and the pores are less than λ / 20, uniformly arranged neatly. The edges of the copper foil should be smooth, flat, prohibited from sharp burrs. It is recommended that the coil edge is greater than the width of the microstrip line greater than or equal to 1.5 W, and H represents the thickness of the microstrip substrate medium.
(4) The RF signal trace is prohibited across the horizontal gap of the second layer.
3. Tape line wiring
The radio frequency signal is sometimes pasted from the intermediate layer of the PCB, and is common to walk from the third layer, the second layer and the fourth layer must be a complete ground plane, ie the eccentric stripline structure. It should be ensured that the structure integrity of the strip line must be required:
(1) The edges of the strip lines are at least 3 W width from the upper and lower places, and there is no non-ground via within the 3 W range.
(2) It is forbidden the RF strip line to span the upper layer of the upper layer.
(3) The same inner strip line should be treated with a packed copper skin and add aperture on the ground copper skin, and the pitch is less than λ / 20, and uniformly arranged neat. The edges of the copper foil should be smooth, flat, prohibited from sharp burrs. It is recommended that the edge of the copper edge is larger than or equal to 1.5 W, or the width of 3h, H represents the total thickness of the upper and lower dielectric layers of the stripline.
(4) If the strip line is transmitted to transmit high-power signals, in order to avoid the 50 ohm lines wide, the copper skin of the upper and lower reference planes of the strip line are usually needed, and the hollow width is a strip line. The total medium has a thickness of more than 5 times, and if the line width is still not required, the upper and lower second layer reference surfaces are again vacated. , Read full text, original title: RF slabs and wiring requirements
Article Source: [Micro Signal: EDN-China, WeChat public number: EDN Electronic Technology Design] Welcome to add attention! Please indicate the source of the article.
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