THERM-A-GAP™ PAD 70TP Family (70TP / 70TPA / 70TPG / 70TPF): Selection, and Applications

Parker Chomerics’ THERM-A-GAP PAD 70TP family is a 7.0 W/m-K, ultra-soft “thermal putty” sheet system offered with four structural options: unsupported (70TP), aluminum-foil/PSA (70TPA), woven-glass offset carrier (70TPG), and woven-glass centered carrier (70TPF). The base compound is exceptionally compliant (≈Shore 00 15) and designed for one-time, static assemblies where the material permanently conforms to roughness and planarity error, driving low contact resistance at very low clamp forces.

Core Material: What’s Common Across All Four

• Thermal conductivity: 7.0 W/m-K

• Operating range: −55 °C to 200 °C

• Electrical: Dielectric strength ~200 VAC/mil; volume resistivity ~10¹³ Ω-cm

• Dielectric properties: εᵣ ≈ 5.6, tan δ ≈ 0.001 (1 MHz, ~2.8 mm)

• Outgassing: TML ≈ 0.10 %, CVCM ≈ 0.03 %

• UL 94 V-0; RoHS

• Compression behavior (unsupported 0.120″ example): ~18 % @ 5 psi, ~42 % @ 10 psi, ~63 % @ 25 psi, ~73 % @ 50 psi

Design implication: The combination of high conductivity and very low modulus allows reliable heat-spreading at modest assembly loads and broad tolerances, particularly for board-to-chassis interfaces and component stacks that cannot tolerate high clamp force.

The Carrier & Adhesive Options—What Changes by Suffix

• 70TP (no suffix): Unsupported sheet (no carrier, no PSA).

• 70TPA (“A”): Aluminum-foil carrier with a pressure-sensitive acrylic adhesive (PSA) on one side.

• 70TPG (“G”): Woven-glass carrier, offset toward one face; no PSA.

• 70TPF (“F”): Woven-glass carrier centered through the thickness; no PSA.

Note: Carriers are not liners. Carriers reinforce the pad and stay with the part; liners are removable release films. Do not remove carriers during assembly.

Mechanical & Assembly Behavior by Variant

1) 70TP (Unsupported)

• Best for: Maximum Z-conformability at the lowest force; narrow keep-out areas where added carrier thickness or in-plane stiffness is undesirable.

• Handling: Softest and most fragile; rely on both liners until final placement to prevent stretching/tearing.

• Rework: Intended for one-time assembly—expect permanent set after compression.

2) 70TPA (Aluminum-Foil Carrier + PSA One Side)

• What it adds: A thin aluminum foil improves pick-and-place robustness, shear stability, and adds a factory-applied acrylic PSA for permanent attachment.

• Thermal nuance: Foil can modestly assist in-plane heat spreading, but the dominant path remains through-thickness.

• When to pick it: Vertical or overhead placements, automation with light vacuum tooling, or field installs where PSA prevents pad shift during final torque.

3) 70TPG (Woven-Glass Carrier, Offset to One Face; No PSA)

• What it adds: Reinforcement with a “clean-break/low-tack” interface on the glass-carrier face. This improves tear resistance and handling while keeping the opposite face fully compliant.

• When to pick it: Prototyping and light rework scenarios, large die-cuts where pad stretch is a risk, or interfaces needing asymmetric surface behavior.

• Design note: Because the carrier is offset, slight asymmetry in compression response can appear at very low loads.

4) 70TPF (Woven-Glass Carrier, Centered; No PSA)

• What it adds: Symmetric reinforcement with the carrier at mid-plane for balanced compression and reduced risk of edge tearing on big footprints.

• When to pick it: Large panels, modules with frequent handling before final clamp, or applications needing handling gains without adhesive commitment and without the one-sided “clean-break” bias of G-carrier.

Thickness, Tolerance, and Force Planning

• Standard sheet thicknesses: 0.030–0.200″ (0.76–5.08 mm).

• Tolerance: ±10 % for ≤0.100″ and ±0.010″ above 0.100″.

• Force window: Expect deflection of 20–70 % depending on load and thickness; confirm actual bond-line thickness in your hardware.

Application Mapping (Where Each Variant Excels)

Typical targets include telecom equipment, board-to-chassis interfaces, BGAs, memory modules, GPUs/CPUs, and industrial devices.

Assembly Tips (to Protect Performance)

1. Place first, then peel liners. Prevents stretch and contamination.

2. Don’t remove carriers. Carriers are structural; removing them compromises performance.

3. Mind one-time set. The “thermal putty” matrix is meant to permanently conform; plan rework paths accordingly.

4. PSA = commitment. With 70TPA, the PSA simplifies assembly but reduces repositionability.

Spec Box (Quick Reference)

• W/m-k: 7.0 W/m-K

• Hardness: ~Shore 00 15

• Thermal impedance (example): ~0.27 °C-in²/W @ 10 psi, 1 mm, G-carrier

• Electrical: ~200 VAC/mil dielectric strength; ~10¹³ Ω-cm volume resistivity

• εᵣ / tan δ (1 MHz): ~5.6 / 0.001

• Use temp: −55 °C – 200 °C

• Regulatory: UL 94 V-0; RoHS; low outgassing (TML ~0.10 %, CVCM ~0.03 %)

More Information

• Choose 70TP when maximum conformity is needed at the lowest forces and careful handling is possible.

• Choose 70TPA when you need PSA and the handling advantages of an aluminum-foil carrier.

• Choose 70TPG when you want offset glass for a cleaner release and easier rework/prototyping.

• Choose 70TPF when you want centered glass for symmetric compression and robust handling on large areas.