Most thermal pad RFQs arrive as a width x length dimension and a thickness - which is like ordering a gasket without holes. The pad arrives as a die-cut part, and the details (corner radii, tolerances, liner format, mounting holes) decide whether it drops onto the line or becomes a hand-fit problem. This guide lists what to specify, from the shop floor's point of view.
The drawing: nine details that matter
- Outline with radii. Sharp internal corners tear during die-cutting and peeling. Give inside corners a radius of 0.5 mm or more, or accept a design revision proposal.
- Thickness with tolerance. State nominal and acceptable range (e.g. 0.5 mm ± 0.05). Tolerance drives both cost and conformity - unrealistically tight tolerances price the pad for no benefit.
- Holes and cutouts. Screw holes, locating pins, connector windows. Minimum web between cutouts is typically 1 mm; below that, the part distorts on the liner.
- Orientation-critical features. If the part is asymmetric, add an orientation mark so assembly cannot install it rotated.
- Liner choice. Single- or double-sided liner; release force matters for automated pick-and-place (low-tack liner for vacuum nozzles).
- Reel format. For volume assembly: kiss-cut on reels, pitch and reel width matched to the placement machine.
- Adhesive option. Pads can carry a PSA face for vertical surfaces - note this raises contact resistance slightly, so use it only where mechanical retention demands it.
- Exposed graphite edges. On pad-plus-plate stacks, decide whether the plate's cut edges need sealing or edge protection in your environment.
- Identification. Part number on the liner (inkjet) keeps mixed kits honest on the assembly floor.
Tolerances: what die-cutting delivers
| Feature | Practical tolerance | Comment |
|---|---|---|
| Outline dimension | ± 0.15-0.25 mm | Depends on part size; tighter is possible but rarely needed |
| Hole position | ± 0.2 mm | Relative to outline; datum on the drawing |
| Thickness | ± 0.05 mm typical | Material-dependent; confirm per grade |
| Minimum web / slot width | ~1.0 mm | Below this, parts distort or tear on peel |
These are die-cutting norms for elastomer-graphite composites, not our maximum capability - but designing to them keeps the part cheap and repeatable. If your stack genuinely needs tighter, tell us why and we will quote it properly.
From drawing to sample
The practical sequence: send a DXF/PDF with the details above plus gap and pressure data → we confirm manufacturability and propose corrections (usually corner radii and tolerance relaxations) → die-cut tooling is cut in-house → samples ship with the impedance report, typically within about two weeks for standard materials → you validate in the fixture, we adjust → pilot at 10-100 pieces, production at 1000+.
Two common mistakes
First, specifying the pad solid where a relief hole is needed: pads compressed over screw bosses bulge and can lift adjacent interfaces. Second, forgetting peel behaviour: a pad that sticks to its liner too well slows manual assembly, one that releases too early jams automated placement - release force is a spec, not an accident.
Send us the drawing as it is; half the value of the first reply is the manufacturability review. Samples from one piece, worldwide from Ningbo.