Adhesive tapes for EMI shielding above 10 GHz
As of 2020, 5G technologies are being built and sold, even though a 5G global network is a few years away yet. As with any new technology on the horizon, however, there are potential challenges that the industry is still working out how to address. Electromagnetic compatibility (EMC) for 5G devices is one of those concerns.
Electrically conductive tapes for assembly and enclosure-level shielding have been used for years to achieve EMC, but special care must be taken when selecting these materials for 5G.
The high-band wireless spectrum that’s been newly allocated for 5G is higher than anything that’s come before it. In fact, it ranges from 20 to beyond 300 GHz. By wavelength, that’s 0.5 to10mm, hence the name “millimeter-wave” (mmWave).
Anything above 18 GHz presents a risk because the wireless signals and noise can interact with the materials in unpredictable ways. For example, tapes that previously worked to pass low or mid-band EMC regulatory tests may fail at this new high-band.
Except for certain circumstances, when testing materials to work with mmWave or microwave frequencies, circuits operating above 6 GHz are typically not taken into account. This means specification sheets are often unhelpful for applications above 6 GHz.
EMI-specific tapes rarely extend ASTM D4935, the common standard for shielding effectiveness, above 10 GHz. This is not to say shielding for 5G is insurmountable. Rather, it underscores the importance of first learning about the new materials and working with qualified specialists in regards to advanced adhesives, tapes, gaskets, and epoxy or resins that are suitable for 5G’s millimeter band.
5G EMI shielding is also challenging because millimeter waves can “leak” into enclosures through seams, joints, hinges, thru-holes, and other apertures of sub-millimeter geometries. Tapes can be used to shore up these ingress points to attenuate external EMI penetrating enclosures. However, other solutions must be used when working with internal interference on the board and with component-level EMC/EMI in the millimeter band.
The EMI tapes
- For gasketing: One important part use of EMI tapes is gasketing, where vents, thru-holes, or conduits are sealed with gaskets made from materials that offer high-shielding effectiveness. Sometimes the tape is die-cut to form the gasket itself. Thick tapes often include carriers such as foam or rubber, a single-sided metallic coating, and an electrically conductive or insulating adhesive that affixes to internal faces of enclosures around the gasketed punchouts.
Additionally, double-backed elastomeric tape is frequently used to adhere and bond specialized gaskets for EMI attenuation to metal enclosures. The tape’s adhesive ensures mechanical bonding, while the elastomer is impregnated with conductive particles to electrically bond with and conduct EMI from the gasket to shield or ground.
- For prototypes and shielding repair: Other tapes, made from copper or aluminum films, or flat-woven/braided tapes, are used to increase the shielding effectiveness of an enclosure by applying them across gaps and seams of interior or exterior enclosure surfaces.
Although this is more common in prototyping, troubleshooting, and repairs of larger enclosures or high-power wireless devices (as found in RADAR, maritime, avionics, and electrical construction), metallic woven and film tapes occasionally find use in electronic device production as well.
The age of the millimeter-wave is here, with hundreds of millions of smartphones, tablets, and laptops shipped that have baseband ICs and antennas using 28 GHz and 39 GHz. Moreover, in the 2020-21 timeframe, expect to see miniaturized RADAR at 75-79 GHz enter automotive production lines.
The Internet of Things, or IoT, which interconnects with 5G, is also expected to pump one trillion new electronic things into the world in the next decade. And this trillion will all emit EMI.