3M CN-4490 is a single-sided EMI shielding tape constructed of a copper-plated woven polyester carrier and a conductive acrylic pressure-sensitive adhesive. The product is used for shielding and grounding of electronic enclosures, printed circuit board-to-chassis grounding, cable wrap, and die-cut pad applications. The woven carrier provides conformability over curved seams; it should not be confused with continuous copper foil tapes. Manufacturer typical data list total tape thickness at 0.120 mm, peel adhesion to stainless steel at 4.0 N/10 mm when tested under ASTM D1000-17, and surface resistivity below 0.05 Ω/sq under ASTM D257-14. Shielding effectiveness is specified from 30 MHz to 1 GHz at 75 dB to 85 dB under IEEE Std 299-2006. These are manufacturer typical values; final assembly qualification must be performed on the actual flange and closure geometry.

When the tape is applied to clean metal flanges, the conductive adhesive establishes a low-resistance interface through the thickness of the tape. The tape is not intended as a primary current-carrying conductor in high-current circuits. If continuous current exceeds 1 A, a separate copper strap or ground wire is required. The product is classified for EMI shielding and electrostatic discharge control rather than power distribution.

Published data for CN-4490 above 1 GHz are limited. Qualification at higher frequencies should be performed on the assembled enclosure because shielding effectiveness is influenced by seam geometry, aperture size, cable entry treatment, and mating flange pressure.

What process limits govern roll-fed lamination and die-cutting of the metallized woven carrier?

Because the carrier is woven polyester rather than solid copper foil, slitting and die-cutting behavior differ from metal-foil-backed tapes. Slit widths down to 3 mm are feasible with hardened rotary shear knives. Below that width, exposed fiber ends along the slit line can fold into the adhesive face and create non-conductive regions. Die-cutting with matched metal tooling at clearances between 0.025 mm and 0.050 mm is used to reduce edge burr and fiber pullout. Tooling wear is higher than with unplated polyester films because metallized fiber ends accelerate edge degradation on steel rule dies.

At application temperatures below 10 °C, the acrylic pressure-sensitive adhesive exhibits reduced wet-out on low-surface-energy enclosure coatings. Production lamination commonly uses a heated nip roller at 40 °C and 0.28 MPa to initiate adhesion. Final peel strength develops over 24 h at 23 °C. Lamination speeds above 20 m/min can trap air beneath the woven carrier, producing voids that increase contact resistance. For manual application, a 2 kg roller passed twice over the tape is the minimum procedure listed in the manufacturer’s application notes.

Humidity during application should be controlled. At relative humidity above 60% RH, moisture adsorption on metal flanges can delay adhesive bond formation and produce visible edge lifting. Pre-drying of the substrate with clean dry compressed air or an isopropanol wipe is specified before tape placement. Solvent wiping must be followed by a drying period of at least 60 s to avoid solvent entrapment at the adhesive interface.

In enclosure seam shielding, 3M CN-4490 is applied over pre-cleaned metal flanges with a minimum overlap of 5 mm across the joint. The conductive adhesive is not a substitute for mechanical closure. Contact resistance at the tape-to-flange interface is proportional to the applied pressure from enclosure screws or clamps. On aluminum flanges with chromate conversion coating, the surface should be cleaned and dried before application. Uncoated copper, nickel-plated steel, or tin-plated steel flanges provide a more stable long-term interface. If the enclosure is exposed to condensing humidity, a seam-seal coat over the tape edge is specified to prevent electrochemical degradation of the copper-plated carrier.

Electrical performance is controlled by overlap geometry, adhesive filler distribution, and substrate potential.

The conductive acrylic pressure-sensitive adhesive contains conductive particulates that provide through-plane conductivity. The listed contact resistance below 0.1 Ω applies to clean, flat copper or steel test fixtures at a defined overlap and pressure. In field use, rough castings, thick e-coat layers, anodized surfaces, or oxide-heavy substrates can raise contact resistance significantly. For low-noise analog circuits or high-frequency return paths, the tape should be applied directly to bare metal or a stable conductive finish.

Contact resistance should be verified with a four-wire measurement method rather than a two-wire ohmmeter because probe lead resistance and probe contact resistance can mask the actual interface value. Test coupons should be prepared with the same flange finish and closure force as production assemblies. The manufacturer’s internal test method for contact resistance uses a 25 mm overlap and a defined contact pad geometry; this does not directly represent a curved enclosure seam or a die-cut pad under screw compression.

The shielding effectiveness of the woven carrier is lower at frequencies above 1 GHz than continuous copper foil because the weave apertures can limit field attenuation. Manufacturer data for CN-4490 above 1 GHz are limited. Assemblies requiring validated shielding above 10 GHz should not rely on this product without additional enclosure-level testing under the applicable standard, such as IEEE Std 299 or the project-specific emission requirement.

The conductive adhesive is not a continuous metallic shield. Its filler network provides electrical continuity but may exhibit batch-to-batch variance in filler distribution at die-cut edges. Production lots should be sampled for surface resistivity and peel adhesion after die-cutting, not only on the incoming roll, because cutting can disturb the adhesive layer at the perimeter and expose non-conductive adhesive regions.

When CN-4490 is substituted for copper foil tapes, mechanical conformability and termination method determine the selection.

Compared with 3M 1181 copper foil tape, 3M CN-4490 offers higher tear resistance and lower crease memory after repeated flexing. The woven polyester carrier bends around compound enclosure radii without the permanent creasing that can occur with thinner copper foil. The trade-off is lower continuous shielding above 1 GHz and a woven surface that is more difficult to solder than solid foil. Compared with 3M 1245 embossed tin-plated copper foil tape, CN-4490 is not specified for solder termination at reflow temperatures above 260 °C because the polyester carrier and acrylic adhesive do not survive solder bath exposure.

For reel-to-reel die-cutting, the woven carrier of CN-4490 requires more frequent blade maintenance than solid foil tapes because the metallized fibers are abrasive. The advantage is reduced splitting along the die-cut perimeter when pad geometries include narrow neck regions, provided the cutting depth is controlled. Laser cutting is possible but introduces a heat-affected zone at the adhesive edge; processed pads should be checked for charred fibers and adhesive carbonization that can increase contact resistance.

Storage conditions in the manufacturer technical data specify a shelf life of 24 months from date of shipment when stored in original packaging at 21 °C and 50% RH. Rolls should not be stored in direct sunlight or near ozone-generating equipment because the acrylic pressure-sensitive adhesive and copper plating are sensitive to long-term oxidation. Compliance documentation includes RoHS 2011/65/EU. For applications subject to REACH, the specific adhesive formulation must be checked against the latest candidate list because product composition can change without changing the commercial part number.

For die-cut grounding pads used between a printed circuit board and a metal chassis, 3M CN-4490 is converted into pads that are placed between the bare-metal chassis pad and the printed circuit board ground area. Closure force from screw compression should be sufficient to produce uniform adhesive contact over the entire pad. The pad is not used as the only mechanical fastener; a metal screw or clip is required to maintain low contact resistance over thermal cycling. In thermal cycling between -40 °C and 70 °C, adhesion loss at the outer edge of the pad is the primary observed failure mode when the substrate surface energy is below 38 dyn/cm. Corona or plasma treatment is then used before lamination to raise the surface energy of low-energy plastics or powder-coated surfaces.

When the tape is applied to zinc-plated steel enclosures, galvanic compatibility with the copper-plated carrier must be considered. In cyclic humidity testing under IEC 60068-2-30, exposed copper plating can show visible oxidation product at the tape edge after 48 h. A polyurethane or acrylic conformal coat over the applied tape edge is specified in marine and outdoor telemetry enclosures. The conductive adhesive itself is not a moisture barrier; its filler network can transport moisture along the tape-fiber interface, and the sealing edge must be continuous to prevent undercutting.