GPU in photo, background clusters

Thermal Gap Fillers, Softness with Armor HD300 versus HD300TG

HD300: Ultra-compliant 2.7 W/m·K gap filler for wide tolerances, low clamp loads, and high conformability.

HD300TG: Same as HD300 core plus a Tgard™ fiberglass-reinforced silicone liner for cut-through/puncture resistance and >6 kV AC dielectric barrier; surface is non-tacky for cleaner handling and easier placement.

The HD300 Platform: Designed for Compliance

The HD300 series is built for environments where you need excellent thermal transfer without stressing sensitive components, or warping thin PCBs. Its soft silicone base compresses easily to conform to uneven surfaces, filling air gaps and lowering thermal resistance without requiring high clamping force.

Key strengths of the HD300 core:

• Maintains thermal performance over multiple assembly cycles

• Provides stable dielectric isolation

• Accommodates large variations in gap height

• Minimizes stress on solder joints and fragile components

If you have a mixed stack-up with variable tolerances, the HD300 can “bridge the gap” without overloading one area while starving another.

What the “TG” Brings to the Table

The HD300TG is the same compliant HD300 core, but with a Tgard™ carrier bonded to the surface. This fiberglass-reinforced silicone film acts like a protective shield:

Advantages of the TG liner:

• Cut-through resistance: Protects against damage from screw heads, standoffs, burrs, and sharp casting edges

• Dielectric strength: Provides a robust >6 kV AC electrical barrier for high-voltage designs

• Surface cleanliness: Non-tacky liner resists dust and fiber pickup during handling

• Placement control: Easier to move into position without the “stick” of a bare pad

Because the liner adds mechanical toughness, HD300TG is often chosen for assemblies where the thermal pad is in direct contact with hard hardware features or exposed fasteners.

Related Variant: HD300MTG

The MTG variant moves the Tgard layer inside the pad (≥0.040″ thickness). This configuration maintains tacky surfaces on both sides for grip during assembly while still gaining the liner’s cut-through protection and dielectric performance.

Choosing Between HD300 and HD300TG

Core Specs That Matter

• Thermal conductivity: 2.7 W/m·K (both)

• Thickness range (TG): 0.5–5.0 mm in 0.25 mm increments

• Standard sheet sizes: 9″×9″, 18″×18″ (custom die-cuts common)

• Hardness: Shore 00 ~38

• Flammability rating: UL 94 V-0

• Volume resistivity: ~1.2×10¹⁴ Ω·cm

DFM & Assembly Best Practices

1. Torque control: Even though the TG liner resists screw bite, always use standoffs, bosses, or torque-limiting fasteners to prevent over-compression.

2. Gap measurement: Capture min/typ/max gap heights across your assembly—design for the maximum to avoid overstressing components.

3. Edge management: Use rounded corners and avoid sharp interior cutouts in die designs.

4. Surface prep: Keep liners in place until just before install to avoid contamination; wipe mating surfaces with IPA.

5. Pilot testing: Run a small batch and record temperature deltas at expected compression levels to finalize your torque recipe.

Part Numbering Quick Guide

• HD3xx = thickness in mils (e.g., HD340 = 0.040″)

• HD360TG = HD300 at 0.060″ with Tgard liner on top

• HD380MTG = HD300 at 0.080″ with Tgard layer in the middle

Typical Applications of HD300 & HD300TG Thermal Pads

HD300 excels in:

• Server CPU, GPU, and accelerator cards

• Router line cards with horizontal mounting

• Consumer electronics with large flat heatsinks

• Industrial control boards with consistent clamp pressure

HD300TG is the better fit for:

• Screw-mounted VRM and memory heatsinks

• Telecom modules with rough cast housings

• Power electronics with exposed hardware features

• Any high-voltage module needing extra insulation margin

Final Takeaway

If your design is all about compliance and ease of rework, HD300 is a dependable workhorse. If your design environment is mechanically punishing or electrically demanding, HD300TG adds the armor layer you need without giving up the softness and thermal performance of the base material. NEDC manufactures thermal pads through die-cutting, and waterjet cutting.