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TIM Pads, Gap Fillers, Graphite Spreaders, or Aerogel: Choosing Power-Module Thermal Materials
Power-equipment heat is two problems wearing one name. The path problem moves losses from a module into a sink, and every mil of material in the joint is resistance the junction pays for. The boundary problem keeps a hot compartment from cooking its neighbors, and is judged by entirely different methods.
The H-O power module thermal management application page covers both, and this guide walks its eleven families by the decision each one wins, with methods named by designation: ASTM D5470 for thermal impedance, ASTM D149 for dielectric strength where the joint must isolate, ASTM C177 and ASTM C411 for blanket insulation, ASTM E84 and UL 1709 for fire behavior, and UL 94 for flammability classes.
Per-grade values quoted are the maker-TDS and dossier figures cited on the parent page.
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The path: four ways through the joint
Reinforced pads: the flat, clamped joint
A flat, well-clamped module wants the thin reinforced construction: PROTECT pads (the 1500FG grade reports 1.5 W/m·K, UL 94 V-0, and -100 to 204 °C service per its TDS) or Sil‑Pad TSP grades up to the 3.5 W/m·K class. The reinforcement takes screw force without cutting through; the silicone carries the heat. Where the interface must also isolate electrically, dielectric strength per ASTM D149 on the TDS is the second gate, covered in depth on the drive-insulation side of this estate.
Gap fillers: the uneven stack
A toleranced, multi-height stack wants the soft Gap Pad filler that conforms instead of bridging: TGP grades at 1.0, 1.5, 3.0, and 5.0 W/m·K, service -60 to 200 °C, gauges from roughly 0.010 to 0.250 inch per TDS, with softness classes to the ultra-soft grade. The filler trades some bulk conductivity for full-footprint contact, which usually wins on uneven stacks.
Graphite: the grounded joint and the sideways move
Graphite does two different jobs, and the difference is direction. As a TIM, compressible eGRAF HiTherm graphite (5, 10, and 20 mil laminate classes, UL 94 V-0 per TDS, with the compressible high-temperature grade at -40 to 400 °C) carries grounded module and baseplate joints where isolation is handled elsewhere, and usually wins the thermal comparison there.
As a spreader, SpreaderShield natural-graphite films exploit the material's anisotropy: in-plane conductivity far exceeds through-plane, so a thin film under a hot component moves the heat sideways into structure and sink area the component cannot reach. Read both directions from the TDS; a spreader is not a through-path TIM, and a spreader with nowhere to send its heat just relocates the problem.
Adhesive films: the fastener-free spreader
Where the spreader, lid, or small sink mounts without hardware, a SECURE thermally conductive adhesive film carries both the attachment and the thermal path; the 1500KT2 grade reports 53.1 kV/mm dielectric strength per ASTM D149 on its TDS in a thin-film bond line. The bond is permanent, so flatness, cleanliness, and rework policy are process decisions to settle before the line runs. H-O laminates adhesive film to SpreaderShield as a single peel-and-place part.
The boundary: blankets, thin aerogels, and barriers
Aerogel blankets: the most insulation per inch
ArmaGel aerogel blanket (seven grades mapped per the dossier) is the compartment-insulation workhorse, with conductivity per ASTM C177 and hot-surface methods per ASTM C411 on its TDSs and the HTF grade citing UL 1709 rapid-rise fire exposure. Pyrogel XTE takes the hottest blanket duty, rated to 650 °C per the dossier: hot bus ducts, engine bays, exhaust-adjacent compartments.
Both are installation-sensitive: compressed or soaked aerogel loses what you bought it for, so the cut geometry must preserve loft and the edges want treatment where moisture is real.
Thin aerogels: when there is no room for blanket
SLENTEX mineral-aerogel panels (standard and FR grades per the dossier) insulate walls and covers at panel thickness, and AeroZero thin polymer aerogel film covers electronics-adjacent layers where millimeters decide. The same installation rule applies: aerogel performance lives in its structure, so fastening must locate without crushing.
Fire and heat barriers: protect what is next door
ManniGlas glass-fiber paper (1200, 1900, 1902, 2000) is the inorganic fire barrier against radiant heat, with UL 94 listings per TDS; mica sheet carries the same duty into arc-adjacent compartments. The BISCO specialty silicone foams split the heat-shield roles: the RF‑120 heat-shield foam beside hot zones, the FPC fire-rated foam barrier in and around electrical equipment, and the IF‑200 tear-resistant construction for frequently opened panels.
SOLIMIDE polyimide foam adds the aerospace-class FST data set (smoke density per ASTM E662, flame propagation per FAR 25.856 on its TDS, UL 94 V-0 on one grade); the project audit flags it as most justified in nuclear-grade and similarly high-spec installations.
Path and Boundary Families Side by Side
| Family | Job | Electrical role | Temperature position (per TDS / dossier) | Typical role |
|---|---|---|---|---|
| PROTECT / Sil‑Pad TSP | Path (through) | Insulating | -60/-100 to 180/204 °C classes | Flat, clamped module-to-sink joints |
| Gap Pad TGP | Path (through) | Insulating | -60 to 200 °C | Uneven stacks, tolerance chains |
| eGRAF HiTherm graphite | Path (through) | Conductive | To 400 °C (compressible grade) | Grounded joints, hot interfaces |
| SpreaderShield | Path (sideways) | Conductive | Per grade TDS | Lateral hot-spot spreading to real sink area |
| ArmaGel / Pyrogel XTE | Boundary | n/a | Pyrogel XTE to 650 °C per dossier | Hot compartments, bus ducts, walls |
| SLENTEX / AeroZero | Boundary | n/a | Per grade TDS | Space-critical thin insulation |
| ManniGlas / specialty foams | Barrier | n/a | Inorganic paper; foams per TDS | Fire and heat shields beside hot zones |
Illustrative and relative only; confirm each grade on its current technical data sheet. Path comparisons per ASTM D5470 at your pressure; boundary insulation per ASTM C177 / C411; fire behavior per ASTM E84 and UL 1709 class methods as cited per grade.
Two rules that sort the page
First, the temperature ceiling comes from the TDS, not the family name: silicone TIM grades carry wide but finite windows, graphite extends the ceiling where the joint can be conductive, and past that the problem changes character and becomes boundary insulation.
Second, fire barriers and insulators are not interchangeable: ManniGlas and mica resist flame and radiant heat superbly and are modest bulk insulators; aerogel blanket is a superb insulator whose fire behavior is grade-specific. Where a wall needs both, the two-layer construction is normal, and H-O laminates barrier and insulation as one converted part.
How H-O Products helps
H-O Products is a precision die-cut converter, not a raw-material producer. We take pad, film, blanket, paper, and foam stock from the material manufacturers and die-cut, CNC knife-cut, kiss-cut on liner, slit, and laminate it to your drawing, with material traceability and lot-code TDS records under our ISO 9001:2015 certified quality management system in Winsted, Connecticut.
We recommend a family and grade direction from your gap, clamping force, electrical role, temperature, and boundary requirement, and grade-level values are confirmed against the manufacturer's current TDS.
Frequently asked questions
Thicker pad or thinner pad: which way do I err?
Err toward the measured gap, not toward either instinct. Resistance grows with every mil, so the thinnest pad that still fills the worst-case gap at your clamping force is the right answer. Tolerance the gap honestly (height spread, bow, torque relaxation), and compare candidates per ASTM D5470 impedance data at your pressure on the TDS. Thinner buys path and risks coverage; thicker buys coverage and costs path.
What does a SpreaderShield film do that a TIM does not?
It moves heat sideways. Natural-graphite spreaders exploit the material's anisotropy (in-plane conductivity far exceeds through-plane, both per ASTM D5470 on the TDS) to carry a hot spot laterally into sink area, cold wall, or chassis mass the component cannot reach. A TIM shortens the path through the joint; a spreader relocates the heat to where a path exists. A spreader without a destination just shares the problem with the neighbors.
ArmaGel or Pyrogel for my hot compartment?
Choose by temperature and exposure. The ArmaGel family covers most compartment, duct, and wall duty, with conductivity per ASTM C177 and hot-surface methods per ASTM C411 on the TDSs, and the HTF grade citing UL 1709 rapid-rise fire exposure. Pyrogel XTE takes the hottest blanket duty, rated to 650 °C per the dossier. Both are installation-sensitive: specify cut geometry that preserves loft and edge treatment where moisture is real.
ManniGlas, mica, or aerogel: which is the fire barrier?
Name both requirements and they sort themselves. ManniGlas glass-fiber paper and mica sheet are inorganic barriers: superb against flame and radiant heat, modest as bulk insulation. Aerogel blanket is the insulator, with fire behavior that is grade-specific (the HTF grade cites UL 1709; SLENTEX has an FR grade per the dossier). Where a wall needs both steady-state insulation and a fire rating, the two-layer construction is normal, laminated by H-O as one converted part.
Get a power-module thermal recommendation
Tell us the gap and flatness, the clamping force, the electrical role of the joint, the service temperature, and any boundary insulation or fire-barrier requirement, and we will recommend a family and grade direction and quote die-cut parts to your drawing.
Samples typically ship in 3 to 5 business days for common die-cut configurations on materials we keep on hand; standard production runs about two weeks after drawing approval; expedited service is available. MOQ varies by material and part.
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Last updated · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).
References
- ASTM D5470 (thermal impedance of thin thermally conductive solids; compare at your pressure and thickness); ASTM D149 (dielectric strength where the joint must isolate).
- ASTM C177 (steady-state thermal conductivity, the blanket method); ASTM C411 (hot-surface performance); ASTM E84 (surface burning); UL 1709 (rapid-rise fire exposure, cited on the ArmaGel HTF TDS).
- ASTM E662 and FAR 25.856 (smoke density and flame propagation, cited on the SOLIMIDE TDS); UL 94 (flammability classes, per grade); IEC 61439 / IEEE C37.20 (assembly standards).
- Manufacturer technical data sheets and dossier entries: TIM pads, gap fillers, graphite TIM and spreaders, adhesive films, aerogel blankets, thin aerogels, glass-fiber paper, specialty silicone foams.
This article summarizes thermal material-selection principles for power modules and equipment compartments using the families and published methods cited on the parent application page. Comparisons are qualitative; per-grade values quoted are maker-TDS and dossier figures and must be confirmed on the manufacturer's current technical data sheet at your gauge, pressure, and installed condition.
All parts are custom manufactured to order; minimum production run quantities vary by material and part. H-O is a die-cut converter, not a raw-material producer, and does not independently certify materials or finished assemblies.