Improve shielding in enclosures fabricated from PCB

Created: Jun 2023

PCB is often used to build enclosures for RF projects [1-3]. However, the enclosures' ability to shield RF interferences is not discussed.

The enclosure have lids to allow access. The lids are typically fastened with screws at the corners and are supposed to electrically contact the thin copper layers on the "walls" (fig. 1).

Fig. 1: Enclosure fabricated from PCB. It has inherently poor RF shielding due to hairline gaps between lids and the 'walls'.

Unfortunately, the small contact area between the lids and the sides / "walls" does not ensure a reliable electrical connection. Moreover, the lids may not make contact over their entire length due to warpage. The lid to wall gap is microscopic, but, nevertheless will degrade shielding. The longer the enclosure's sides, the worse is the shielding degradation.

Going back to the project shown in fig. 1, it encountered interference at ~200 MHz and ~960 MHz (fig. 2, peaks marked as "RFI?")

Fig. 2: Measured noise figure (black trace) of the project in fig. 1 showed interference peaks (RFI?) at ~200 MHz and ~960 MHz

One way to eliminate this inherent defect in PCB enclosures is to wrap copper tape around the walls's edges to increase its contact area (fig. 3-5). We used 1 cm wide self-adhesive copper tape for this purpose.

Fig. 3: An enclosure with 1 cm wide copper tape wrapped around the PCB edges

Fig. 4: Another enclosure with copper tapes wrapped around the PCB edges to enlarge the contact area with the lids. Additionally, the lid has BeCu fingers to contact the shield in the enclosure center

Fig. 5: perspective view of the enclosure in fig. 4

References

[1] B. Shriner & P. K. Pagel, "A step attenuator you can build", QST, Sep. 1982. Available: https://www.arrl.org/files/file/Technology/tis/info/pdf/September1982_Attenuator.pdf

[2] V. Antonic, "How to Build Beautiful Enclosures from FR4 — aka PCBs", Available: http://hackaday.com/2015/06/03/how-to-build-beautiful-enclosures-from-fr4-aka-pcbs

[3] "Fabricating a chassis from clad PCB board material", Available: https://qrpbuilder.com/wp-content/uploads/2016/11/pcb_chassis_a.pdf

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