Saint-Gobain CHR C665 is a single-faced pressure-sensitive tape in which a rolled copper foil backing is combined with an electrically conductive acrylic adhesive. The product is supplied in roll form for electromagnetic interference shielding, grounding, and surface current-carrying applications where soldered or mechanical joints are not available. Manufacturer-published nominal dimensions include a backing thickness of 0.036 mm, an adhesive thickness of 0.040 mm, and a total thickness of 0.076 mm. The backing is a 1 oz rolled copper foil; the adhesive layer is formulated to provide a low-resistance path through the z-axis rather than acting only as a bond film. Typical property comparisons are reported under ASTM D3330/D3330M for peel adhesion and ASTM D3759/D3759M for tensile strength and elongation.

Why Would a Copper Foil Tape Need a Conductive Acrylic Adhesive Rather Than a Standard Acrylic Bond Line?

With a conventional non-conductive adhesive, the tape may shield a seam but does not ensure a direct current path between the foil and the substrate through the adhesive. In CHR C665, the conductive filler system lowers the bulk resistivity of the bond line. Manufacturer data list z-axis resistance below 0.05 Ω when tested between the copper foil and a prepared conductive substrate under a controlled electrode fixture. This value is a system property rather than an intrinsic adhesive property; oxide films, chromate conversion coatings, anodized layers, and machining oils can elevate apparent contact resistance well above the tape specification. For enclosure seams of plated steel or aluminum, the conductive adhesive permits a shunt path across a junction without requiring a separate ground finger. Production-line experience indicates that apparent peel to galvanized surfaces is strongly influenced by surface contamination; the manufacturer’s published peel value is referenced to polished stainless steel, not to an as-received casting or extrusion.

Application of the 0.076 mm composite on a motorized lamination station requires closed-loop unwind tension control. Copper foil has a lower yield strain than polyethylene terephthalate or polyimide backings; step changes in tension beyond the elastic limit create longitudinal wrinkles that cannot be removed after pressure is applied. On rotary die-cutting lines, the tape is usually kiss-cut without cutting the release liner; worn die blades or excessive side force can produce burr edges and reduce clearance to adjacent traces. Full adhesive bond strength is approached only after a dwell period, often 24 h at 23 °C and 50 % relative humidity. Initial tack is lower than final peel; therefore, immediate handling should avoid shear loading until the adhesive has developed cohesive strength. A controlled-pressure roller or hydraulic platen press is used to wet out the adhesive on flat surfaces.

These values are manufacturer-published typical data, not batch certification limits. Lot-to-lot variation is controlled by the supplier’s process control, but users should verify incoming material using identical dwell time, substrate preparation, and test speed because ASTM D3330/D3330M allows multiple panel finishes. For overhead or vertical installations, a shear holding test under ASTM D3654/D3654M is often added to the incoming inspection plan.

The Acrylic Bond Line: Temperature Boundaries, Surface Preparation, and Thermal Cycling Failures

The adhesive is a pressure-sensitive acrylic rather than a thermosetting film. It develops adhesion through wetting and bond formation, not heat cure. Manufacturer-published continuous service boundaries are −40 °C to 155 °C. Below −40 °C, adhesive rigidity rises and peel force under impact becomes rate-dependent; above 155 °C, oxidative aging of the acrylic polymer and accelerated copper oxidation reduce bond stability. Use near 155 °C requires qualification of the entire assembly because the adhesive can soften before the copper foil loses mechanical integrity. Copper has a coefficient of linear thermal expansion near 17 × 10⁻⁶ K⁻¹; the acrylic layer is viscoelastic and its dimensional change is time-dependent. On extruded aluminum housings, thermal cycling between −40 °C and 85 °C can create edge flagging where the tape is terminated without a mechanical wrap or clamp. Extending the tape edge 2 mm to 3 mm around a seam is a documented production remedy for early flagging.

Surface preparation is generally limited to cleaning and oxide removal. Solvent wiping with 70 % isopropanol and 30 % deionized water is commonly used; ketone or aromatic solvents that soak into the exposed adhesive edge can swell the acrylic and reduce holding power. For aluminum, chromate conversion coatings improve corrosion resistance but may reduce the conductive path; the user must determine whether the coating can be locally removed without compromising enclosure corrosion performance. Low-energy plastics such as polypropylene and high-density polyethylene may require corona or atmospheric plasma treatment; published peel data for these substrates is limited.

Application at substrate temperatures below 10 °C can increase adhesive elastic modulus and lower initial tack. Production lines in cold environments may require warming the tape and substrate to 18–25 °C before lamination. Condensation on the copper foil must be avoided because trapped moisture under the foil can later promote galvanic activity at exposed copper edges. At relative humidity above 60 %, the acrylic adhesive continues to build bond strength, but the copper surface may tarnish before application; pre-cleaning and immediate lamination reduce the resulting contact-resistance drift. Rolls should be stored in original packaging away from ozone-generating equipment and direct ultraviolet exposure. Inventory control should follow first-expired-first-out practices according to the manufacturer’s shelf-life statement; indefinite stability should not be inferred.

In comparison with copper foil tapes that use silicone pressure-sensitive adhesives, CHR C665 has a lower continuous heat limit but avoids silicone migration in paint or coating operations. Silicone-adhesive copper foils are preferred where service exceeds 180 °C or where low outgassing is specified under ASTM E595. The acrylic system is compatible with many painted and plated metal surfaces but is not a substitute for silicone adhesive in high-temperature masking or polyimide-film applications.

Compared with copper foil tapes that use non-conductive acrylic adhesives, CHR C665 provides a through-plane conductive path rather than only in-plane shielding. Non-conductive acrylic tapes still shield a seam if the foil is continuous, but they do not replace a grounding finger or screw; conductive adhesive is specified when the bond line itself must maintain a low-resistance shunt. The conductive filler in the adhesive may reduce wet-out on low-energy substrates and can restrict the use of the tape on clear or optically inspected joints because the tape is opaque.

Aluminum foil tapes are lower in material cost and easier to slit, but electrical conductivity of aluminum is approximately 62 % of copper at equivalent cross-section. Contact between copper foil and aluminum housing can create a galvanic couple if moisture and electrolyte are present; design should isolate the copper surface from the aluminum substrate with a compatible conductive coating or exclude moisture at the seam. CHR C665 is chosen where copper conductivity and solderability are required, not where aluminum weight or cost is the controlling specification. Tin-plated copper foil tapes are available where improved solderability and oxidation resistance are required. Bare copper CHR C665 has higher initial surface conductivity but forms oxide films over time; tin plating can reduce surface oxidation at the expense of a different contact potential. In environmentally sealed enclosures, bare copper may be acceptable; in humid or marine exposure, edge sealants or conformal coatings are specified.

When Is CHR C665 Preferred over Plated Fabric or Conductive Foam Shielding Products?

Copper foil tape differs from copper-plated fabric tapes in that the foil is a continuous metal sheet rather than a woven or nonwoven textile coated with a conductive finish. The continuous sheet offers high shielding effectiveness for flat seams, ground planes, and straight-line shielding, but conformability around complex radii is lower. Plated fabric tapes are preferred for cable bundles and irregular gasket surfaces because the fabric stretches and returns; CHR C665 is selected when a continuous, solderable copper surface is required. Local soldering is possible, but the acrylic bond line beneath the foil degrades under excessive heat; heat shielding and fast cooling are used to prevent adhesive discoloration and loss of tack adjacent to the solder joint.

Published CHR C665-specific shielding effectiveness data under IEEE 299 or the historical MIL-STD-285 method are limited; enclosure seam geometry, aperture size, and contact pressure control final attenuation. The tape should therefore be evaluated in the assembled enclosure rather than as a stand-alone shielding array. The foil is unsupported and puncture resistance is low; over sharp sheet-metal edges, a polyimide or polymer reinforcement is used when edge damage is a known production risk.

Regulatory documentation is supplied through a Saint-Gobain certificate of conformance. RoHS status is referenced to Directive 2011/65/EU as amended by (EU) 2015/863, and REACH obligations are assessed under Regulation (EC) No 1907/2006. The product is not marketed as a food-contact or medical-grade material; users must perform migration, biocompatibility, and ignition-risk assessments for those environments. A UL 94 flame classification should not be inferred from the copper foil alone because the adhesive layer may contribute to ignition or flaming behavior.