Thermal Paste, Pads & Insulator Kits
Thermal Management
Metal surfaces only touch at microscopic high points — the rest is insulating air. Interface materials fill those gaps: paste for best conduction, pads for convenience and gap-filling, mica/silicone kits when the joint must also block electricity.
What it looks like
Thermal Paste, Pads & Insulator Kits
A typical thermal management — exact shape, colour and markings vary between manufacturers.
Types & variants
Key specs
Thermal conductivity
W/m·KGeneric paste ~0.8–1, quality paste 4–12, pads 1–6. Higher = better transfer. (Copper is ~400 — even good paste is the bottleneck, so keep layers thin.)
Electrical isolation
kVMica and Sil-Pads withstand 2–4 kV; standard paste is non-conductive but not a rated insulator; some exotic pastes conduct — keep them off pins.
Thickness / gap
mmPads come in fixed thicknesses to bridge uneven gaps; paste layers should be as thin as possible.
Durability
yearsCheap paste dries and cracks in a few years ('pump-out'); pads and quality pastes last much longer.
Markings
Tubes/sheets are labelled with W/m·K and, for insulators, breakdown voltage. Mica washers are recognisable transparent flakes cut to TO-220/TO-3 outlines.
Standard values
TO-220 insulator kits: mica washer + nylon shoulder bushing. Pads: 100×100 mm sheets in 0.5/1/1.5/2 mm. Paste: 1–4 g syringes. Thermal adhesive: two-part epoxy or double-sided tape for LED stars.
How to choose
1) Flat machined surfaces → thin paste layer (rice-grain amount, spread thin). 2) Uneven or multi-chip gaps → pads of the right thickness. 3) Live tab on a grounded sink → mica + shoulder washer or Sil-Pad, then verify isolation. 4) No mounting hardware possible (LED stars) → thermal adhesive. 5) More is not better — excess paste insulates.
Pinout & package
Consumables, not components. Application order for an insulated TO-220: paste — mica — paste — sink, screw through the shoulder bushing so the screw doesn't short the tab.
Example circuits
- Re-pasting a laptop CPU/GPU that thermal-throttles
- TO-3 power transistor on a chassis with mica kit in a vintage amplifier
- Gap pads coupling RAM chips and VRMs to a one-piece cooler plate
- 10 W LED star glued to a salvaged sink with thermal epoxy
Common failures
Dried, cracked paste after years of heat cycles (rising temps, throttling), pinholed or cracked mica (tab shorts to chassis — can be catastrophic), pads torn on disassembly, and conductive paste smeared across component pins.
How to test
IR thermometer: large chip-to-sink temperature gap = failed interface. After insulated mounting, always continuity-test tab to heatsink (must be open). Old paste that's powdery on inspection needs replacing — clean with isopropyl alcohol before re-pasting.
Substitutes
Quality pastes interchange freely; pads must match thickness. In a pinch, generic silicone grease beats nothing by a wide margin. Never substitute the insulator with plain paste when the tab is live — that 'works' until it arcs.