What Should We Do for the PCB LAYOUT in RF Product Design?

After purchasing the RF module, we may start the PCB Layout, but what should we do when we making the Coplanar Waveguide PCB LAYOUT of our products? This article mainly introduces the PCB Layout precautions of the RF circuit, which is surrounding the RF module. The main purpose is to help you correctly design the PCB routing when using our RF modules, so as to ensure the RF performance and reduce the design cycle of the products. Referring the below figure with the numeric symbol, there are six tips to note:

1)    Strictly control the Microstrip Linewidth (W) and Ground Clearance (S) corresponding to 50-ohm coplanar waveguide. For example, with the common PCB plates as FR4 media (dielectric constant 4.2) and copper coating thickness 35um, the Microstrip Linewidth (W) and Ground Clearance (S) corresponding to the different signal layers are shown in Table 1. It is particularly reminded that PCB factories need to control Microstrip Linewidth (W) and Ground Clearance (S) accuracy.

2)    The PIN here is no need to do a thermal pad, but should be in full contact with the ground.

3)    The surface layer is paving forbidden (slightly) to reduce Parasitic Effects. The RF line should be as short as possible, and it is best to avoid routing at right angles. If there is a corner, it is recommended to go 135 degrees.

4)    When connecting the components package, it should be noted that the signal pin should be kept at a certain distance from the ground. Refer to above Figure. Please do not lay copper at the bottom of the signal pad.

5)    Please ensure the integrity of the reference ground layer corresponding to the RF routing, and increase the grounding hole to help the RF return, and keep the distance between the ground hole and the signal line at least twice the line width. Ensure that the grounding area of the same layer of RF line is as large as possible, the reference ground of the other side should be also as complete as possible, and ensure that a certain number of ground holes are connected to two layers of ground.

6)    The π type matching circuit is a must, which is normally constituted of 3 components (as shown in above Figure). When designing, the pad should be placed close to the antenna. If the space between the antenna connector (SMA) and the RF pin of the module is not enough (impossible to place the three components of the π matching circuit), it can be changed to an L-shaped matching circuit.

Note: C1, R1 and C2 are reserved matching circuits to optimize the RF performance of the antenna. The default value is: R1 = 0R Resistance; C1 = NC; C2 = NC

Supplementary Instruction:

1. Sensitive IC should be away from RF module or shielding

2. Pay attention to antenna directionality. Normally the antenna should be vertical stand on the base board.

3. The product shell (especially above antenna part) shall not be electroplated, or metal material

Click Here DreamLNK RF Layout Application Guide V2.3  to download the complete document.

This INSTRUCTION is applicable to all the Sub-1GHz and 2.4GHz RF modules produced by DreamLNK, which include 433/868/915MHz RF modules, 2.4G RF modules, FSK transceiver modules, Bluetooth modules, LoRa modules, UART module, etc. You may visit our website to know more about our RF modules! If any product meets your demand, please feel free to contact us!