Fibreglass-reinforced insulation pads for TO-220, TO-247, TO-264 and TO-3P power packages, plus silicone thermal pads from 1.5 to 6 W/m·K for board-level stages. Every pad is die-cut to the package outline — mounting hole included — or to your drawing.
The defining problem in power electronics assembly is that a semiconductor's mounting tab is usually electrically live while the heatsink it must be bolted to is grounded. The part between them has to do three incompatible things at once: conduct heat efficiently, withstand the voltage across that joint, and survive being clamped with real force against a machined surface.
Plain silicone handles the first two and is vulnerable on the third. A burr or machining ridge on the heatsink face can cut or puncture a soft pad during tightening — and a puncture in this location is a short from a live tab to chassis. Fibreglass-reinforced pads exist for exactly this duty: the woven glass carrier resists cut-through and gives the part enough mechanical integrity to be handled, placed and clamped repeatably in production.
That is also why these parts are supplied as die-cut shapes matched to specific package outlines with the mounting hole already punched, rather than as sheet stock to be trimmed on the bench, where hole position and edge quality would vary from one operator to the next. We hold ten stock shapes across the TO-220, TO-247, TO-264 and TO-3P package families, each available in five fibreglass material grades, and we die-cut anything outside the stock list to your drawing.
A bolted power device is a simple stack with demanding physics. Heat leaves the silicon through the package tab, crosses the insulation pad into the heatsink, and spreads to ambient. Electrically, the same joint separates the tab potential from a grounded heatsink; mechanically, it is a clamped joint tightened to a torque figure from the semiconductor datasheet.
Every requirement lands on one thin layer. Its conductivity sets the thermal path, its dielectric strength sets the voltage the joint can hold off, and its reinforcement decides whether it survives assembly at all. The sections below give the stock shapes, the five material grades behind them, and the board-level silicone pads used elsewhere in the assembly.
The ten shapes below are held as stock die-cuts, sized to the package outline with the mounting hole pre-punched where the package calls for one. Anything outside the table — other outlines, notches, tab clearances — is die-cut to your DXF or PDF drawing.
| Package | Size | Mounting hole |
|---|---|---|
| TO-220 | 13 × 19 mm | 3.5 mm |
| TO-220 | 15 × 20 mm | 3 mm |
| TO-247 | 17 × 22 mm | 3 mm |
| TO-247 | 17 × 22 mm | 3.5 mm |
| TO-247 | 20 × 26 mm | 3 mm |
| TO-247 | 20 × 26 mm | 3.5 mm |
| TO-247 | 17 × 27 mm | — |
| TO-264 | 22 × 28 mm | — |
| TO-3P | 19 × 24 mm | — |
| TO-3P | 25 × 22 mm | — |
Every shape is available in all five fibreglass material grades listed below. MOQ for die-cut TO shapes is 50 pieces. Full range detail is on the fibreglass-reinforced section of the thermal catalogue.
Five fibreglass-reinforced silicone grades cover 1.0 to 2.0 W/m·K in thicknesses from 0.20 to 0.45 mm. Every stock shape is available in every grade, and the same grades can be die-cut to a custom outline.
Away from the bolted device, driver and control boards use unreinforced silicone pads in higher conductivities. Three grades cover board-level work, each from 0.5 to 3 mm with adhesive or plain backing, and each with its own technical datasheet.
| Grade | Conductivity | Dielectric strength | Thickness options | Adhesive | Datasheet |
|---|---|---|---|---|---|
| CP150 | 1.5 W/m·K | 4.5 kV/mm | 0.5 / 1 / 2 / 3 mm | Adhesive or plain | TDS |
| CP300 | 3.0 W/m·K | 6.0 kV/mm | 0.5 / 1 / 2 / 3 mm | Adhesive or plain | TDS |
| CP600 | 6.0 W/m·K | 6.0 kV/mm | 0.5 / 1 / 2 / 3 mm | Adhesive or plain | TDS |
MOQ 10 sheets for sheet grades · die-cut TO shapes start at 50 pieces.
Neoprene is the one material on this page that is not a thermal interface material. Neoprene sheet and closed-cell neoprene foam are stocked in 1, 2 and 3 mm, non-adhesive, for cushioning, sealing and vibration isolation around assemblies — and we publish no thermal conductivity for them.
Grades most often specified for power electronics assemblies, drawn from the live catalogue. The fibreglass TO-package shapes are listed in the tables above.
Supply terms. Standard sheet grades start at 10 sheets; die-cut TO-package shapes start at 50 pieces. Catalogue grades are typically dispatched within 7 days. Parts to a new drawing are quoted per job — send a DXF or PDF with the grade and thickness, and note that die cost is one-time, so the per-part price falls sharply with volume. Adhesive and non-adhesive options are available across the silicone grades. ISO 9001:2015, supplied to OEMs and contract manufacturers across India from Bengaluru.
We hold ten stock die-cut shapes across those four package families, each available in five material grades from 1.0 to 2.0 W/m·K and 0.20 to 0.45 mm. The table above lists the sizes. Anything outside it is a die-cut to your drawing.
Because of clamping. A woven glass carrier resists cut-through from burrs and machining ridges on the heatsink face, which is the failure that matters here — a puncture at that joint shorts a live tab to chassis. The carrier also makes the part robust enough to place repeatably on a production line.
It clears the fastener that clamps the device to the heatsink, so the pad stays captive and correctly aligned as the screw is tightened. Supplying the hole pre-punched to the package's own dimension is what keeps alignment consistent unit to unit.
Yes — interface resistance falls as contact improves, so a joint tightened to the device manufacturer's specification performs better than a loosely fastened one. Follow the semiconductor datasheet's torque figure; over-tightening risks damaging both the package and the pad.
No. Neoprene sheet and foam are supplied for cushioning, sealing and vibration isolation, and we do not publish a thermal conductivity for them. If you need heat transfer, use a silicone or fibreglass-reinforced pad.
Send your specification — grade, thickness, size or die-cut drawing, and quantity — and our team will quote to your requirement.