The Silicone Thermal Pad TO-3P (25mm x 20mm) is an electrically insulating, thermally conductive interface pad designed for mounting heavy-duty power semiconductor packages (such as TO-247, TO-3P, and TOP-3) securely to metal heatsinks. Engineered with high-grade silicone elastomer reinforced with a tear-resistant fiberglass core, these pre-cut pads deliver reliable dielectric breakdown isolation up to 4kV+ to eliminate electrical short circuits to grounded heatsinks while filling microscopic surface voids to enhance heat transfer. Supplied in a convenient 10-piece pack, they are ideal for prototyping, DIY audio amplifier builds, repair workbenches, and low-volume electronics assembly.

Specifications

• Product Type: Thermally Conductive Electrical Insulator Pad
• Compatible Packages: TO-3P
• Dimensions: 25mm (Length) x 20mm (Width)
• Thickness: 0.3mm (±0.05mm)
• Mounting Hole Diameter: Pre-punched ~3.5mm center mounting screw hole
• Material: High-Grade Silicone Elastomer with Woven Fiberglass Core Reinforcement
• Thermal Conductivity: 1.2 W/m·K to 1.5 W/m·K
• Dielectric Breakdown Voltage: ≥ 4.0 kV AC (4000V)
• Volume Resistivity: ≥ 1.0 × 10¹² Ω·cm
• Operating Temperature Range: -50°C to +200°C
• Flammability Rating: UL94 V-0 equivalent flame retardant
• Pack Quantity: Approx. 10 Pieces (Retail / Prototype Pack)

Features

• High Dielectric Isolation (4kV+): Safely isolates high-voltage transistor tabs (MOSFETs, IGBTs, BJT power transistors, rectifiers) from grounded chassis and heatsinks to prevent short circuits and electrical hazards.
• Fiberglass Reinforced Core: Prevents tearing, puncture, and deformation under high mechanical mounting torque or sharp metal heatsink burrs.
• Pre-Cut & Pre-Hole Punched: Accurately stamped to 25x20mm with a center screw hole for fast, drop-in assembly without manual cutting or trimming.
• Wide Temperature Stability (-50°C to +200°C): Retains elasticity and thermal conductivity without drying out, cracking, or degrading over extended operating cycles.
• Clean & Reusable: Clean, mess-free alternative to thermal grease alone; easy to reposition during testing and repairs.

Common Applications

• High-Power Transistor Mounting: Thermal isolation for TO-247/TO-3P MOSFETs, IGBTs, BJT power transistors, and SCRs/Thyristors.
• Audio Power Amplifiers: Class-AB and Class-D discrete output transistor mounting to common chassis heatsinks.
• Switch-Mode Power Supplies (SMPS): Primary switching bridge transistors and secondary ultra-fast rectifier heatsink isolation.
• Solar Inverters & UPS Systems: Insulating high-voltage power switching stages mounted to shared aluminum heatsinks.
• Motor Drivers & DIY Projects: High-current BLDC, DC motor speed controller, and benchtop power supply builds.

Usage Tips

• Surface Preparation: Ensure both the heatsink surface and the transistor mounting tab are completely clean, deburred, and free from dust or metal shavings before placement.
• Insulating Bushing / Washer: Always use a matching plastic/nylon insulating shoulder washer (TO-220/TO-3P bushing) with the mounting screw so the metal screw does not create an electrical bridge between the tab and heatsink.
• Torque Control: Tighten mounting screws evenly (recommended 0.5 to 0.8 N·m) to achieve optimal thermal contact without crushing or cutting through the pad.
• Optional Thermal Grease: While these pads can be used dry for clean assembly, applying a micro-thin layer of thermal paste on both sides further reduces contact thermal resistance for extreme power dissipation.