Parker Chomerics THERMATTACH T418 Thermally Conductive Attachment Tape is a double-sided, pressure-sensitive acrylic adhesive film that contains a ceramic filler to reduce thermal resistance while retaining electrical isolation. The product is supplied on a release liner in sheet or die-cut format and is used for bonding heat sinks, heat spreaders, and certain power discretes to aluminum plates, coated metal housings, and FR-4 board surfaces. The T418 suffix identifies a nominal thickness of 0.018 in (0.457 mm); the manufacturer reports a bulk thermal conductivity of 0.7 W·m⁻¹·K⁻¹ when evaluated under ASTM D5470. Because the adhesive system is silicone-free, the tape is specified in assembly environments where siloxane migration from silicone gap pads or greases would contaminate optical surfaces, relay contacts, or conformal coating adhesion.

The thermal resistance of the adhesive layer alone is approximately 1.0 °C·in²·W⁻¹ when calculated from the nominal thickness and published bulk conductivity. This value excludes contact resistance at the two mating surfaces. In a real assembly, the measured thermal impedance is higher if the substrate is not flat, if lamination pressure is insufficient, or if air pockets remain within the bond line.

In production lamination, the primary process risk is a substrate condition that prevents acrylic wet-out. Solvent wiping with isopropanol or a 70:30 isopropanol/deionized water blend is used to remove ionic contamination and light oils; heavily oxidized aluminum may require abrasion with a nonwoven pad followed by a final solvent rinse. Polymeric substrates with surface energy below approximately 38 dyn·cm⁻¹ may require corona, plasma, or primer treatment before tape application. The adhesive bond is formed by pressure, not by vulcanization or air cure; the bond strength available immediately after lamination is lower than the final value. A dwell period of 24 h to 72 h at 25 °C is generally specified before full shock-and-vibration validation.

A servo-driven pneumatic lamination station with a flat 6061-T6 aluminum platen and a 60 Shore A silicone pressure pad is commonly used. Lamination pressure is maintained at 15–30 psi (0.10–0.21 MPa) for 10–20 s; pressures above 30 psi can force the acrylic adhesive laterally and create a non-uniform bond line. In high-volume lines, a heated platen at 40–60 °C may be used to accelerate wet-out, but liner removal must be validated because heat can alter release liner peel force. Vacuum hold-down fixtures are used to prevent substrate movement during die-cut tape placement.

Failure modes observed on manufacturing lines include air entrapment along the leading edge of a die-cut part, uneven bond-line thickness due to heat sink warpage, and partial liner release during automated handling. Acoustic microscopy is used to detect void fraction in the bonded area; void fractions above 5% are commonly treated as a reliability risk in power-semiconductor heat dissipation, although the acceptance threshold is design-specific.

What distinguishes T418 from lower-thickness T4xx tapes when interface flatness is uncertain?

The practical selection difference concerns the amount of non-planarity that can be tolerated before void formation dominates thermal resistance. With a nominal thickness of 0.018 in, T418 provides more conformability than a 0.006 in or 0.010 in tape in the same family. For a flat, polished interface, a thinner T4xx grade has a lower bulk conduction resistance: a 0.006 in tape would be approximately one-third of the bulk resistance of T418, assuming equivalent filler loading. However, on a stamped aluminum heat sink with typical waviness, a thin tape cannot fill the gap, and the resulting air layer increases the measured thermal impedance beyond the thin tape’s bulk value. The correct use of T418 is therefore not for minimum thermal resistance in a flat assembly, but for reliability when the flatness deviation exceeds the usable range of thinner tapes and when adding a separate gap pad is not acceptable.

In a design with a 0.010 in maximum surface irregularity, T418 retains some bond-line thickness after conforming, whereas a 0.010 in tape would be marginal. The trade-off is that the bulk conduction term scales directly with thickness; design calculations should use the bonded thickness, not the nominal pre-assembly thickness. The manufacturer’s thermal impedance curves should be consulted for specific pressure and substrate combinations; published data for this specific configuration is limited outside the standard flat-platen test.

These calculations are not a substitute for measured thermal impedance, because contact resistance can dominate in dry interfaces. The presence of three layers—adhesive, filler, and substrate—makes the lumped interface resistance dependent on clamping pressure, surface roughness, and adhesive wet-out. At low lamination pressure, the contact resistance term may be larger than the bulk tape term.

Dielectric strength, volume resistivity, and peel adhesion data

At 0.018 in thickness, the first-order dielectric withstand voltage is 3.6 kV based on a reported dielectric strength of 200 V/mil under ASTM D149. This is a material-level value; printed circuit board clearance and creepage requirements per IEC 62368-1 or IEC 60664-1 still apply. The reported volume resistivity of 1.0 × 10¹⁰ Ω·cm under ASTM D257 positions T418 as electrically isolating for low-voltage power control circuits, but it is not a substitute for a safety-rated insulation system in high-voltage primary-to-secondary boundaries.

Peel adhesion to aluminum 6061-T6 and stainless steel is evaluated according to PSTC 101. The acrylic PSA develops functional handling strength within minutes, but full peel values are typically reached after the stated dwell period. Because adhesion is sensitive to surface roughness, plating chemistry, and ambient humidity, die-cut part trials on the actual production substrate are required before fixing heat sink mass and overhang dimensions. A heavy heat sink in a vertical orientation may require additional mechanical support during adhesive dwell unless the bond area and dwell time are validated.

During thermal cycling, the CTE mismatch between an aluminum heat sink and a copper leadframe can impose shear strain on the adhesive layer. The acrylic matrix relaxes stress over time, but it is not an elastomer. Qualification for power modules should include thermal shock per JESD22-A104 or IEC 60068-2-14 at the expected operational extremes. Bond-line voiding after cycling is inspected by acoustic microscopy; a void fraction above 5% is generally treated as a reliability risk in power-semiconductor heat dissipation, although the acceptance criterion is product-specific.

In compressed silicone gap-pad assemblies, a clip or spring maintains pressure across the interface. T418 replaces that mechanical pressure mechanism with an adhesive bond; the part-count reduction can simplify the bill of materials, but the interface becomes semi-structural and is not freely separable. Compared with thermal grease, T418 does not pump out under repeated thermal cycling and does not spread onto adjacent board features, but its bulk thermal conductivity is lower than many metal-oxide greases and its minimum bond line is thicker. Compared with a liquid adhesive, T418 requires no mixing, no metering, and no oven cure, but it cannot fill gross gaps and it is more sensitive to surface cleanliness.

The silicone-free acrylic chemistry differentiates T418 from silicone thermal pads and silicone-based tapes in optics, relays, and coating environments. When a silicone pad is replaced with T418, the assembly designer should re-evaluate thermal resistance because the acrylic tape is not as soft as a Shore 00 class gap pad and may not wet out into rough surfaces without higher lamination pressure.

When an acrylic PSA interface must be reworked on a production line

If a heat sink is mispositioned after lamination, rework is possible but not indefinite. Acrylic PSA softens with heat; a heated platen or local hot-air source set between 80 °C and 120 °C is used to reduce peel strength while a low-angle shear force separates the parts. Excessive temperature above the service limit may discolour the adhesive or soften some polymer substrates. Residue after separation is removed with isopropanol; solvent selection must be checked against the substrate because ketones can craze polycarbonate and acrylic housings. The tape is not specified for repeated mounting and demounting; after the first removal, a fresh die-cut T418 part is applied.

Compliance documentation for T418 includes RoHS 2011/65/EU with the 2015/863 delegated directive and a manufacturer supply chain statement for REACH SVHC. Storage is in a sealed polyethylene bag at 10–30 °C and 30–70% RH; the typical shelf life is 12 months from the date of manufacture. Material older than the stated shelf life should be trial-laminated because release liner peel force can increase and wet-out on some surfaces may decrease.