8 Replies Latest reply on Nov 4, 2019 10:23 PM by BoonT_56

    [CYBT-343026-01] About PCB clearance

    YoJa_3107936

      Hi

       

      The customer is trying to develop a small product and is currently struggling with module placement. They would be grateful for any advice on the placement.

       

      Please let us check the 3 items.

      1, According to 7.3 described in AN96841, it is described that there is a significant effect within 7mm in 7.3.1, but the minimum clearance of 5mm in 7.3.2.

      If the distance to the resin part is 4mm, will it be noticeably affected? (They want to get a 1mm margin)

      2,Is the recommended clearance for AN96841 7.3.2 from the module edge or the antenna pattern?

      3,Does the module require resin and distance in the horizontal direction as well?

       

      Please refer to the drawings for details.

       

      Clearance.JPG

       

      Thanks

      Yang

        • 1. Re: [CYBT-343026-01] About PCB clearance
          BoonT_56

          For all practical purposes, you may assume the dimension given is measured from the edge of the PCB. Fig 15 says it all.

           

          1) I did not see a 7mm in 7.3.1. Is this number from another section? In any case, the take away from this section is that the near field

          of the antenna extends up to 4mm from it. This implies that any enclosure (metallic or plastic) must be at least above 4mm in theory.

           

          2) For non-metallic (plastics), the recommendation is at least 5mm. For metallic enclosure, the recommendation is at least 8mm.

           

          For example, the inner wall for a plastic enclosure must be at least 5mm from any of the edges of the module. This especially so for the three

          edges along the antenna.

           

          Do not also forget that there must also be ground clearance underneath the antenna. I hope this clears up a bit.

          1 of 1 people found this helpful
          • 2. Re: [CYBT-343026-01] About PCB clearance
            YoJa_3107936

            Thanks for your advice.

             

             

            Sorry, I wrote a wrong number. Not 7mm, it is 4mm.

             

            The customer asked, if the clearance is 4.2mm (<5), will it have a significant impact?

            • 3. Re: [CYBT-343026-01] About PCB clearance
              BoonT_56

              I can't say for sure what is the impact as these figures are rule-of-thumb or best practices. The only way is to build and measure a prototype. It also depends what is the end product. Categorically, I can say that it should not be a significant impact.

              • 4. Re: [CYBT-343026-01] About PCB clearance
                YoJa_3107936

                I think that there is no problem because

                it seems to be wired in the evaluation board,

                but let me check just in this case.

                 

                 

                Under the module,

                it is natural that the blue and green parts are forbidden to pattern like below picture.

                Is pattern wiring possible for the red part?

                 

                Thanks

                Yang

                • 5. Re: [CYBT-343026-01] About PCB clearance
                  BoonT_56

                  I don't really understand your question but let me just elaborate on the picture above.

                   

                  The picture depicts a view from the top of the module. The red part is the metallic shield over the circuitry. The green part

                  is the area of which the antenna is printed. The blue part is the dimension of the area, for any number of PCB layers below

                  the module, to be cleared of electrical trace. For example, can you imagine a power supply line being routed (on any layer)

                  below the antenna? The performance will be affected. This is the main reason why some clearance is always recommended

                  around the antenna location.

                  • 6. Re: [CYBT-343026-01] About PCB clearance
                    YoJa_3107936

                    Thank you for helping me sort out the problem.

                     

                    >For example, can you imagine a power supply line being routed (on any layer) below the antenna?

                    >The performance will be affected.

                     

                    If I imagine a power supply line being routed below the red part.

                    Will the performance be affected?

                    I think the red part is the module, is not the antenna.

                    • 7. Re: [CYBT-343026-01] About PCB clearance
                      YoJa_3107936

                      Add customer's question

                       

                      As in §7.3.2 and §7.3.3 of AN96841,

                       

                      Is there any reference material that shows how efficiency or VSWRor directivity or gain varies depending

                      on the distance between a non-metal or metal and an antenna?

                       

                      They checked AN91445.

                      Even if it is not this module(CYBT-343026-01), the experiment and examination data by other antennas may be used.

                       

                      Ideally, it would be appreciated if there was data when the distance was changed, such as 2mm / 3mm / 4mm / 5mm ...

                       

                      Thanks

                      Yang

                      • 8. Re: [CYBT-343026-01] About PCB clearance
                        BoonT_56

                        You may lay PCB traces under the red portion. Do minimize though and I would still avoid any clock signals.

                         

                        We do not have any of those antenna performance data as these data are measured by customers and they

                        don't share with us. From the datasheet of the module 343026, you may refer to Table 6 for the antenna

                        specification. You may refer to AN91445 on meandered line antenna for a more detailed treatment.