3M 1345 EMI Shielding Tape is a pressure-sensitive copper foil tape specified for electromagnetic compatibility grounding paths and seam shielding in electronic enclosures. The construction consists of an 0.035 mm embossed copper foil backing and an 0.030 mm conductive acrylic adhesive layer, yielding a nominal total thickness of 0.066 mm excluding the release liner. The adhesive is a particle-filled acrylic system that maintains DC continuity through the adhesive thickness, not only along exposed foil edges. This property distinguishes the material from nonconductive adhesive copper foils used for thermal masking or cosmetic trim, where through-thickness electrical continuity is absent. Embossing is introduced during foil conversion to alter contact pressure distribution at the tape-to-metal interface under low clamping force.

The tape is commonly converted into die-cut shields and grounding strips for board-to-chassis and cable-shield terminations. Because the foil is embossed, the contact path is dominated by high-pressure contact at topographical asperities rather than a single continuous contact plane. On machined or brushed aluminum, the asperity contact reduces the influence of the aluminum oxide layer, which reforms within minutes after abrasion. This behavior is relevant where no secondary mechanical fastener is present and the adhesive alone supplies closure force.

The DC continuity path is influenced by surface roughness, adhesive thickness, and clamping pressure. Manufacturer electrical test methods require a defined electrode area and contact force; comparison of supplier values is not valid unless the test configuration is identical. Surface conductivity and through-adhesive resistance are commonly evaluated by a DC four-point measurement. For enclosure seam shielding effectiveness, published data for this specific configuration is limited; validation under IEEE 299 or EN 50147-1 is required for radiated emissions control. The product is not a primary electrical insulator and is not rated for mains-voltage isolation distances.

What Limits the Adhesion of Conductive Acrylic to Production-Machined Surfaces?

Initial bond strength is controlled by the viscoelastic deformation of the acrylic matrix into substrate topography. On abrasive-blasted or grained aluminum, the adhesive must flow into features of 10 µm to 30 µm; peel strength should not be evaluated immediately after application because dwell time at 23 °C is required for adhesive wet-out. Solvent wiping with isopropanol or methyl ethyl ketone removes processing oils but leaves a transient condensate layer if flash-off time is below 30 s at 21 °C. Application below 10 °C reduces pressure-sensitive tack and can produce lifting at curved seam radii. At relative humidity above 60 % RH, moisture adsorption on metal surfaces can delay void closure and reduce initial adhesion. Production lines using vapor degreasing must verify that chlorinated solvents have evaporated completely before tape placement; residual solvent plasticizes the acrylic and lowers shear strength.

Mechanical properties are foil-dominated. The embossed copper foil resists tensile creep but may develop cracks under repeated flexure at a bend radius below 3 mm; continuous flexure service is not recommended. Die-cutting operations generate higher blade edge wear with embossed foil than with smooth foil, particularly in rotary systems with steel tooling. Liner splitting under excessive unwind tension interrupts automated pick-and-place; the unwind station should maintain constant tension and a controlled peel angle. Paper release liners are sensitive to moisture above 60 % RH and may soften or telescope on high-speed slitting. The tape should not be used as a structural joint or as a primary electrical insulator.

When 3M 1345 Replaces Smooth Copper Foil Tape in Enclosure Seam Grounding

The selection between 3M 1345 and a smooth copper foil tape such as 3M 1181 is driven by interface contact stability. The embossed foil creates localized high-pressure regions at surface asperities, which can displace oxide films on tin-plated steel or copper grounding frames. Smooth foil has a larger continuous contact area on flat machined surfaces and may be easier to clean after application. Under low screw torque from 0.4 N·m to 1.2 N·m, the embossed surface tends to show lower contact resistance to oxidized substrates; on polished flat metal, smooth foil may provide equal or lower resistance. For outdoor enclosures, copper tape edges exposed to salt spray can form nonconductive copper chlorides; contact resistance should be assessed after ASTM B117 neutral salt spray exposure if the product is used outside a sealed gasket region.

Direct copper-to-aluminum contact in the presence of condensed moisture creates a galvanic cell because of the electrochemical potential difference between copper and aluminum. Under repeated humidity cycling, aluminum frame material can corrode adjacent to the tape edge. If 3M 1345 is used on aluminum chassis, the seam should be sealed with a dielectric conformal coating or separated by a tin-plated intermediate layer. This limitation is more severe than for conductive fabric tapes that use nickel-plated or tin-plated fibers. In closed indoor enclosures at 40 % RH to 60 % RH, galvanic corrosion is typically limited. Published salt-fog endurance data for this specific product is limited; qualification should be performed on the complete enclosure assembly.

Roll-Stock Dimensional Controls and Compliance Documentation

Standard slit widths include 12.7 mm, 25.4 mm, 50.8 mm, and 101.6 mm. Roll lengths vary by width and regional stock; converter inventory must be queried for exact length. Lot-specific certificates of analysis should include backing thickness, total thickness, and adhesion values against the specified test substrate. The supplied liner can vary between paper and polymer depending on slitting source. Where a compliance matrix is required, the relevant standards are shown below.

The supplied construction is generally expected to comply with Directive 2011/65/EU as applied to homogeneous materials, but component-level certification requires confirmation from the 3M certificate of compliance for the specific stock number. REACH EC 1907/2006 obligations are lot-dependent for any substances of very high concern above 0.1 % weight-by-weight. Users should not rely on an older compliance letter for new-source slitting. UL 510 recognition, where listed, applies to flame retardancy and does not cover shielding effectiveness.

Conductivity and Solderability Comparisons Against Aluminum-Foil and Fabric Tapes

The embossed copper foil carries a DC bulk conductivity of approximately 5.8 × 10⁷ S·m⁻¹, compared with approximately 3.5 × 10⁷ S·m⁻¹ for aluminum. This difference, together with the solderable surface of copper, makes the tape suitable for grounding points where a solder fillet is required to a cable shield. The 0.035 mm foil thickness also exceeds the skin depth in copper at 1 GHz, which is approximately 2.1 µm, so the foil remains an effective conductor well into the UHF band. Conductive fabric tapes provide higher elongation and better drape over curved surfaces but higher through-thickness resistance than copper foil. Aluminum foil tapes have lower mass per unit area and lower raw material cost but cannot be soldered with standard tin-lead or SAC alloys. The acrylic adhesive of 3M 1345 is less resistant to continuous contact with strong solvents than silicone or epoxy film adhesives; conformal-coat and cleaning-solvent compatibility must be checked before specification.

Store in a humidity-controlled stockroom at 21 °C to 27 °C and 40 % RH to 60 % RH. Under those conditions, conductive acrylic foil tapes of this class typically retain acceptable tack for 12 months from date of manufacture; warehouse excursions above 30 °C for more than 30 days can advance adhesive crosslinking and reduce tack at low temperature. Rolls should remain in original packaging until converting to avoid copper edge oxidation and liner moisture uptake. If the liner shows wrinkles or longitudinal creases after storage, the roll should be conditioned at 23 °C and 50 % RH for 24 h before high-speed die-cutting.