Parker Chomerics THERMATTACH T405 is a double-sided, thermally conductive acrylic pressure-sensitive adhesive tape supplied in die-cut parts or roll form. The product is used to bond aluminum or copper heat sinks, ceramic packages, metal shields, and exposed semiconductor surfaces without liquid adhesive cure, mechanical spring clips, or gap-filling compounds. The standard adhesive layer is specified at a nominal thickness of 0.254 mm (0.010 in) and is protected by differential release liners configured for automated pick-and-place handling. Because the tape is a pressure-sensitive acrylic system, no metering, mixing, pot-life control, or oven cure is required. Bond formation is initiated by pressure-driven wet-out against a clean high-energy substrate and continues through room-temperature adhesive flow.

The acrylic matrix remains electrically insulative after ceramic filler incorporation. The tape is therefore positioned between power device surfaces and grounded heat spreaders provided that the assembly voltage does not exceed the derated dielectric rating. In high-volume surface-mount production, T405 is typically applied after reflow soldering because the rated continuous service temperature is lower than the peak reflow profile. Die-cut geometries can be kiss-cut through the adhesive layer while leaving the carrier liner intact, allowing reel-fed placement on board-level assembly equipment. Tolerances for die-cut outer dimensions are commonly held to ±0.15 mm; corner radii below 1.5 mm increase liner tear frequency during automated liner removal.

Which published thermal and electrical parameters govern T405 selection?

The primary thermal transport value is bulk thermal conductivity measured under ASTM D5470. Supplier-published data for the standard construction list a thermal conductivity of 0.8 W/m·K. From the 0.254 mm nominal thickness, the intrinsic thermal impedance of the adhesive layer is calculated as 3.18 × 10^-4 m²·K/W (0.49 °C·in²/W), excluding interfacial contact resistance. Contact resistance is application-dependent and is governed by substrate roughness, lamination force, oxide thickness, and the presence of silicone or organic residues. The total junction thermal impedance therefore cannot be derived from bulk conductivity alone.

The 5.0 kV AC dielectric strength value under ASTM D149 is a short-term uniform-field result. It is not a continuous working voltage. Insulation coordination requires derating for environmental stress, moisture ingress, electrode geometry, and long-term aging. Volume resistivity is specified at 1.0 × 10¹⁴ Ω·cm under ASTM D257; this value is relevant for leakage-current control in DC bias circuits but does not define partial discharge performance or breakdown under pulse conditions.

The tape is applied after soldering operations on automated lines. A typical sequence places the die-cut part on the semiconductor package or heat sink first, followed by lamination with a compliant rubber nip or roller at 45–65 Shore A durometer. Lamination pressure for this product class is commonly held in the 100–300 kPa range with a dwell of 2–5 s. This pressure window permits the acrylic to flow into surface microtexture without squeezing the adhesive beyond the part perimeter. Full adhesion develops over 24–72 h at 20–25 °C. Adhesion validation is performed on cleaned aluminum or ceramic coupons under ASTM D3330 for peel and ASTM D1002 for lap shear. Coupon values should not be transferred directly to production joints because surface roughness, cleaning chemistry, and heat sink mass alter the stress state.

High-speed liner removal failures are most frequently caused by die-cut corners that are too sharp and by release-liner peel initiation force that is too high for the placement head. For roll-fed die-cut tape, liner peel force is typically controlled by silicone release chemistry and liner thickness. Production lines using vacuum pick-and-place tooling should verify that the exposed adhesive side is not contaminated by liner debris. A continuous reel tension should be maintained low enough to prevent adhesive creep but high enough to prevent telescoping; the specific value depends on reel diameter and die-cut part spacing.

When the adhesive bond line replaces a spring clip or push-pin retention

Substitution of mechanical retention with T405 changes the load path from point compression to distributed tensile and shear stress across the heat sink base. The acrylic layer is viscoelastic, so elevated temperature reduces its load-bearing capacity under sustained load. A conservative design criterion for acrylic pressure-sensitive attachment is to keep continuous tensile stress below 10% of the measured ASTM D1002 lap shear value at the maximum continuous service temperature. The heat sink mass, acceleration, and bond area must be evaluated together. Vibration loads generate combined tensile and shear components that cannot be approximated from a single static lap-shear number. Published data for this specific configuration is limited; qualification should include vibration and thermal cycling on the actual heat sink geometry rather than coupon-level extrapolation.

The thin bond line of T405 reduces the through-plane thermal path compared with mechanical clip or push-pin assemblies that depend on inconsistent point contact. However, the adhesive does not provide the same long-term compressive force as a spring clip. If the heat sink is large, cantilevered, or exposed to continuous fan vibration, edge lifting may initiate at the thinnest adhesive region and propagate inward. Production qualifications commonly inspect for edge creep after thermal cycling from -40 °C to 125 °C with a ramp rate of 10 °C/min and dwell times sufficient to stabilize the heat sink mass.

Compared with thermally conductive greases, T405 provides mechanical attachment and dielectric isolation in a single dry film. Greases can show lower thermal impedance at extremely thin bond lines, but they are susceptible to pump-out under thermal cycling and require secondary retention. Gap-filler pads offer higher compressibility for variable gaps, but their thicker bond lines and lower initial peel adhesion can limit heat sink retention. T405 is selected where the gap is fixed, surface flatness is controlled, and the assembly cannot tolerate silicone bleed or liquid residues. Compared with lightly filled acrylic transfer tapes in the same series, T405 uses higher ceramic filler loading to raise bulk thermal conductivity while retaining die-cut processability. Compared with metal-backed thermally conductive tapes, T405 is lighter and conforms to minor surface distortion but does not provide lateral grounding between the heat sink and board-level shielding.

Surface preparation, humidity, and storage boundary conditions

Acrylic pressure-sensitive adhesives require high-energy substrate surfaces for wet-out. Aluminum and copper substrates should be cleaned with isopropyl alcohol or a semiaqueous cleaning chemistry that leaves no surfactant residue. A target surface energy of ≥ 40 dyn/cm is typical for this class of filled acrylic tape. Low-surface-energy substrates such as polyolefins, powder-coated surfaces, or surfaces contaminated with mold-release compounds may show reduced initial tack and final adhesion. Corona or plasma treatment immediately before lamination can raise the surface energy of polymer substrates, but the treatment decays with time and should be qualified for the production line dwell.

Storage of unopened rolls or die-cut parts is recommended at 10–30 °C and ≤ 60% RH. Shelf life is typically rated at 12 months from the date of manufacture when stored in original packaging. Exposure to high humidity before application can cause moisture absorption at the acrylic surface and reduce initial tack. The adhesive should not be applied to bare copper or aluminum that shows visible oxidation, because oxide films can become the weak boundary layer under thermal cycling. Condensing humidity is a known failure mode for acrylic pressure-sensitive adhesives on bare copper; conformal coating or edge seal may be required if the assembly operates at 85 °C/85% RH or worse.

For vacuum or optical applications, a lot-specific ASTM E595 test should be performed because the standard acrylic system is not automatically low-outgassing. Collected volatile condensable material and total mass loss values are application-specific and should be supplied as part of a source-controlled drawing rather than assumed from generic acrylic tape data. Plasticized PVC jackets or elastomer pads placed in direct contact with the acrylic can extract plasticizer and reduce shear strength over time; this incompatibility is relevant in appliance and industrial control enclosures where plasticized wire insulation contacts the tape edge.

Production qualification should include dielectric withstand after thermal cycling under ASTM D149, adhesion retention after humidity aging, and creep measurement after a heat sink load test at the maximum rated service temperature. The tape does not require a thermal cure, but final bond strength is time-dependent. Process controls should therefore distinguish between handling strength immediately after lamination and fully developed bond strength after the stated dwell period.