The Silicone Thermal Pad TO-3P3 (28mm x 22mm) is an extra-large, electrically insulating, and thermally conductive interface pad engineered for mounting high-power semiconductor packages (including TO-3P3, TO-247, TO-264, TOP-3, and large custom power devices) securely to metal heatsinks. Manufactured from high-grade silicone rubber reinforced with a puncture-resistant fiberglass substrate, these oversized pre-cut pads provide dielectric isolation up to 4kV+, eliminate chassis short circuits, and conform to microscopic surface roughness to maximize heat dissipation. Supplied in a handy 10-piece pack, they are ideal for prototyping, DIY power electronics, audio amplifier repair, and low-volume assembly.

Specifications

• Product Type: Thermally Conductive Electrical Insulator Pad
• Compatible Packages: TO-3P3
• Dimensions: 28mm (Length) x 22mm (Width) (Extra-Large Surface Area)
• Thickness: 0.3mm (±0.05mm)
• Mounting Hole: 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

• Extra-Large 28x22mm Dimensions: Provides extended creepage and clearance margins around large power transistor packages to prevent high-voltage arcing over package edges.
• High Dielectric Isolation (4kV+): Reliably isolates high-voltage transistor tabs (MOSFETs, IGBTs, thyristors, and rectifiers) from grounded heatsinks and chassis metal.
• Fiberglass Reinforced Core: Prevents tearing, puncture, and cutting under high screw-clamping torque or against rough metal heatsink burrs.
• Pre-Cut & Pre-Punched: Precision stamped with a center screw hole for fast, consistent drop-in installation on prototypes and repair benches.
• Wide Thermal Stability (-50°C to +200°C): Retains elasticity and thermal interface properties without drying out, hardening, or cracking over long operational lifespans.
• Clean & Reusable: Clean dry-mount alternative to thermal paste alone, streamlining workbench assembly and minimizing mess.

Common Applications

• High-Power Transistor Mounting: Thermal isolation for TO-3P3, TO-264, and TO-247 high-voltage MOSFETs, IGBTs, and thyristors.
• High-Power Audio Amplifiers: Class-AB and Class-D multi-transistor power output stages mounted to common chassis heatsinks.
• Industrial Solar Inverters & UPS Systems: Insulating high-power inverter switching stages and bridge rectifiers on shared heatsinks.
• Switch-Mode Power Supplies (SMPS): Primary half-bridge/full-bridge switching transistors and secondary rectifier heatsink mounting.
• Heavy-Duty Motor Drives & EV Controllers: Power module mounting in frequency drives, CNC spindle controllers, and electric vehicle controllers.

Usage Tips

• Surface Preparation: Thoroughly clean and deburr the heatsink mounting surface and transistor tabs before assembly to remove sharp metal fragments, dust, or oil.
• Insulating Shoulder Washer: Always use a matching plastic/nylon insulating shoulder washer (bushing) on the mounting screw to prevent the metal screw head from bridging the tab to the heatsink.
• Clamping Torque: Fasten screws evenly (recommended 0.6 to 0.9 N·m) to establish firm surface conformity without crushing or distorting the pad.
• Optional Thermal Grease: In ultra-high-wattage continuous dissipation circuits, applying a micro-thin coat of thermal paste on both sides of the pad further minimizes contact thermal resistance.