Server & Network Thermal Interface Materials
H-O Products die-cuts and kiss-cuts thermal interface materials into the pads, spreaders, and multi-part kits inside data-center and telecom electronics: conformable gap fillers for CPU/GPU/ASIC stacks, thin graphite for optics modules, natural-graphite heat spreaders for line cards and FPGAs, electrically insulating pads for power shelves, and weather-tolerant silicone TIMs for outdoor radio units, built to your drawing.
Built for: 1U/2U server boards, switch and router line cards, QSFP/OSFP optics cages, UPS and rack power-shelf interfaces, and RRH/O-RAN radio enclosures, with thermal values per the maker TDS (impedance per ASTM D5470, pressure-dependent) and equipment frameworks such as Telcordia GR-487 and GR-3108 cited by designation at the system level.
To pick thermal interface materials for server and network hardware, sort each interface by gap, isolation, and exposure. CPU/GPU/ASIC to heat sink across a tolerance stack: a conformable gap filler by thickness and conductivity class — the Gap Pad® TGP family, TGP 1000VOUS ultra-soft through TGP 5000. Optics cage (QSFP/OSFP) to riding heat sink: thin eGRAF® HITHERM™ HT-1205-class graphite, kiss-cut to the cage window.
Line-card and FPGA hot spots: SpreaderShield™ graphite moving heat in-plane. Interfaces that must also insulate: Sil-Pad® TSP 900-class or PROTECT® 1500FG (D5470 thermal + D149 dielectric on one TDS).
Outdoor radio duties are mapped in the When-to-spec list. Values are per the TDS on file; see the material reference below for ordering details.
Equipment-level, by designation (the evaluation belongs to the equipment maker's tested design): Telcordia GR-487 (generic requirements for electronic equipment cabinets) · Telcordia GR-3108 (generic requirements for network equipment in the outside plant, with its operating-class framework).
Material-level, per the maker TDS: ASTM D5470 (thermal impedance of thin thermally conductive solid materials; pressure-dependent) · ASTM D149 (dielectric breakdown methods on the insulating pad TDSs) · ASTM D3574 (flexible cellular methods, PORON® cushioning grades) · UL 94 (flammability classes on the listed grades, e.g. V-0 on specific graphite and urethane grades per their TDSs).
- CPU/GPU/ASIC gap pads: Gap Pad® TGP 1000VOUS–5000
- Optics module (QSFP/OSFP) TIM: HITHERM™ HT-1205 / HT-1210
- Premium compute interfaces: HITHERM™ HT-C3200
- Line-card / FPGA spreading: SpreaderShield™ SS400-class
- Formed spreader laminates: SpreaderShield™ FLX
- Insulating device pads: Sil-Pad® TSP 900 / TSP 3500
- Low-pressure shelf joints: Sil-Pad® TSP 1600S
- Spreader / sink attach films: SECURE® adhesive films
- Shelf cushioning & fan-tray pads: PORON® 4701-40V0
- Whole-board TIM kit: kiss-cut on liner, kitted in assembly order
Where are you in the spec process?
This page serves engineers who already have a TIM grade on the drawing and engineers still working out which interface needs which family. Pick the path that matches where you are; you don't have to read the rest.
Send a drawing, get a quote
A gap-filler thickness and conductivity class, a graphite TIM or spreader grade, an insulating pad designation, or a complete kiss-cut TIM kit on your drawing.
Skip to the quote form →Work through the six interface jobs
Six numbered jobs (compute gap pads, optics TIMs, line-card spreading, power-shelf interfaces, outdoor radio TIMs, kitted sets), a TIM duty selector, and a side-by-side family matrix with TDS-cited methods.
Start with job 1 →
Where H-O parts do the work
CPU, GPU & ASIC gap pads by thickness and conductivity class
Between a hot package and its heat sink sits a tolerance stack: package height variation, board bow, heat-sink flatness, and clamp travel. The gap filler's job is to absorb that stack while keeping thermal impedance low, which is why compute gap pads are specified by three numbers, not one: nominal thickness, the compression range the pad accepts at the assembly's clamping pressure, and the conductivity class on the TDS.
A pad that is too firm lifts the heat sink and concentrates stress on the die corners; a pad chosen on conductivity alone may sit in the wrong thickness class entirely and run hotter than a softer, thinner alternative that actually wets both surfaces.
What H-O converts. The Gap Pad® TGP family spans the duty range: TGP 1000VOUS ultra-soft viscoelastic for fragile packages and low clamp forces, TGP 1500 un-reinforced for general board duty, and the soft S-class TGP 3000 and TGP 5000 where the conductivity class climbs. Putty-class dispensed or pad-form fillers are quoted by designation per the vendor TDS where a program already calls one out.
H-O die-cuts pads to the package footprint with handling tabs, kiss-cuts multi-pad sets on liner, and holds the tolerances that keep automated and manual placement repeatable. Thermal impedance values are per ASTM D5470 on the maker TDS and are pressure-dependent. [1]
What to send: package footprint and height tolerance, board-to-sink gap stack-up (nominal and worst case), clamping pressure or screw torque, target conductivity class, and quantities. If the gap is unknown, send the two mating drawings; the stack-up math is part of the review.
QSFP / OSFP optics-module TIM pads for riding heat sinks
Pluggable optics are the hardest small interface in the rack. The riding heat sink presses on the module through a cage window at modest spring force, the module slides in and out across the interface for the life of the equipment, and every tenth of a degree matters at 400G/800G optics power levels.
The interface material has to be thin, abrasion-tolerant across insertion cycles, and consistent at low pressure, which is why thin flexible graphite dominates this duty: it delivers low thermal impedance at riding-heat-sink pressures and does not pump out or dry like greases between service events.
What H-O converts. Thin eGRAF® HITHERM™ graphite in the HT-1205 / HT-1210 / HT-1220 thickness designations, kiss-cut to the cage-window geometry with placement tabs so a production operator lands the pad square on the first try. Where a cage design prefers a compliant pad over graphite, thin soft gap-filler classes step in.
Optics-cage pads are small, high-count parts: H-O runs them as CNC knife kiss-cut arrays on liner, dozens per sheet, with lot-code TDS records per shipment. Impedance values per ASTM D5470 on the TDS; read them at the riding heat sink's actual spring pressure, not the datasheet's highest clamp point. [1]
What to send: cage or heat-sink drawing with the window geometry, riding-sink spring force, thickness budget, insertion-cycle expectations, and annual volumes. Per-port pad counts multiply fast; quoting as kiss-cut arrays is usually the cost answer.
Line-card & FPGA heat spreading with natural graphite
Not every thermal problem is a vertical one. Line cards, FPGAs, NPUs, and dense memory banks often have no room for a taller heat sink, but they do have area: chassis walls, card stiffeners, cold plates a few centimeters away. Natural-graphite heat spreaders exploit the material's strongly in-plane conductivity, moving heat laterally from a hot spot to wherever the card can reject it, at a fraction of the mass of a copper spreader.
The spec questions are in-plane versus through-plane conductivity (graphite's two numbers differ by an order of magnitude), the laminate construction, and how the spreader attaches.
What H-O converts. SpreaderShield™ natural graphite in the SS-series sheet designations (SS350 through SS400 and up), plus the FLX laminates where the spreader must fold around a card edge or survive handling as a formed part. H-O spreaders to the component map, laminates PSA backings for attachment, and supplies SECURE® thermally conductive adhesive films (such as SECURE 1500-KT2) where the attach layer itself must carry heat.
One framing sentence applies to every adhesive layer on this page: adhesive performance depends on substrate, surface energy, temperature, exposure, dwell time, applied pressure, surface preparation, part geometry, and assembly method, and final adhesive selection should be validated in the application.
What to send: a board outline with the hot-spot map (component powers and locations), available spreading area and exit path, bend or fold lines, attachment preference (PSA, clamped, bonded), and any flame-class callout. Component-population keep-outs come straight off the CAD.
UPS & battery-shelf interfaces: when the TIM must also insulate
Rack power shelves, rectifiers, and UPS modules add a constraint the compute board does not have: many of their device interfaces sit at line or bus potential, so the thermal layer must also be the dielectric layer. That moves the spec from bare graphite (which conducts electricity) to the reinforced insulating pad class, whose TDSs carry thermal impedance per ASTM D5470 and dielectric breakdown per ASTM D149 on the same sheet.
The second power-shelf duty is mechanical: cells and modules ride on cushioning pads that hold force over years, a compression job rather than a thermal one.
What H-O converts. The Sil-Pad® TSP family: TSP 900 silicone-fiberglass as the general-duty insulator, TSP 1600S for low-pressure joints, TSP 1800ST soft-tack for assembly-friendly placement, and TSP 3500 where the duty climbs; TDS temperature ranges run roughly -60 to +180/200 °C by grade. PROTECT® 1500FG and the PROTECT® pad family cover the same insulating-TIM duty in alternative constructions.
For shelf cushioning and fan-tray pads, PORON® 4701-40V0 microcellular urethane brings ASTM D3574 compression data and a UL 94 V-0 class on its TDS. The full battery-cabinet material stack (fire barriers, cell compression, cabinet gaskets) lives on the data center power & UPS systems sibling page. [5]
What to send: device package style (TO-247, module footprint, busbar lug), mounting pressure or torque, required isolation and any test voltage on the print, operating temperature range, and the joint's flatness situation. State whether the interface sits at potential; that single answer sorts graphite from the insulating pad class.
RRH & O-RAN outdoor radio TIMs with weather exposure
A remote radio head is a sealed, fanless box on a pole: every watt the PA devices make leaves through the enclosure wall, across a TIM, in an environment that swings from winter cold soak to summer solar load. The interface material sees wide thermal cycling, years of clamped service with no maintenance visit, and (at gasketed joints near the enclosure boundary) condensation and humidity.
Silicone-based TIM pads are commonly specified here for their wide TDS temperature ranges and long clamped-service track record; the enclosure itself is the maker's responsibility, commonly evaluated to outside-plant frameworks such as Telcordia GR-487 and GR-3108, cited by designation. [3]
What H-O converts. Insulating silicone pads from the Sil-Pad® TSP family for PA and power devices on the casting, conformable Gap Pad® TGP fillers where shield cans and odd-height components meet the enclosure wall, and HITHERM™ graphite on interfaces where isolation is handled elsewhere and the joint stays clamped. Die-cut edges matter outdoors: parts cut clean to drawing seat evenly and avoid the field trimming that starts most outdoor TIM problems.
Material temperature ranges and aging data are per the maker TDS by grade; weather sealing of the enclosure joint itself is a gasket problem, covered with the cabinet-thermal and OSP-sealing siblings. May be suitable for solar-loaded enclosures depending on grade and clamping design; final material selection should be validated in the application.
What to send: the casting or enclosure-wall drawing, device map with powers, clamp design and pressures, ambient and solar-load assumptions, the operating-class framework the enclosure is evaluated to (by designation), and service-life expectations. If the radio is strand- or pole-mounted, say so; vibration changes the cushioning conversation.
Die-cut & kiss-cut TIM kits on liner, in assembly order
A 2U server can carry a dozen different TIM parts; a line card or radio unit, half that again. Production lines do not want a dozen part numbers in a dozen bags: they want one liner, parts in assembly order, each pad kiss-cut with a tab so it peels in one motion and lands square. Converting is where a TIM spec becomes a manufacturable program, and it is the part of the job H-O owns end to end.
What H-O converts. Every family on this page runs through the same conversion set: flatbed die-cutting for pads and spreaders, CNC knife cutting for kiss-cut kits and prototype-to-production continuity without hard tooling, slitting for roll-fed widths, and kitting that ships one liner (or one labeled kit bag) per unit built. PSA backings and SECURE® thermally conductive films are laminated in-house before cutting.
Because tapes and adhesive films appear in most kits: adhesive performance depends on substrate, surface energy, temperature, exposure, dwell time, applied pressure, surface preparation, part geometry, and assembly method; final adhesive selection should be validated in the application. Kits ship with lot-code TDS records per material, the documentation trail an equipment maker's design evaluation wants to see.
What to send: the TIM bill of materials (or the drawings to build one), assembly order, liner and tab preferences, per-unit part counts, and annual volumes. "Recommend the kit layout" is a valid callout; that is what the engineering review is for.
The decisions that drive a server & network TIM spec
A thermal-interface part is chosen by the gap it fills and the pressure it sees — not by how thick it is.
Decide bondline vs gap first, then choose by thermal impedance at the real mounting pressure. A thicker pad is not automatically cooler; grades carry their own impedance and flame class per TDS.
Show all 5 selection factors tap to expand
Server & network TIM failures you can prevent at spec
Thermal failures show up late — a part that throttles or drifts hot months after build. Every one is preventable in the TIM callout.
The device’s thermal rating assumes a specified interface. Choosing a TIM by thickness, or a flowable paste on a cycling joint, is where these specs go wrong.
Show all 5 failure modes tap to expand
1. Grease or paste on a thermally cycling joint
Fix — specify a dry, non-flowing TIM; flowable fillers pump out over thermal cycles and leave air gaps.
2. A gap pad chosen by thickness, not impedance
Fix — select by thermal impedance per ASTM D5470 at the actual mounting pressure.
3. An over-thick pad forcing components or boards
Fix — size the pad to the real gap so it fills without loading the assembly.
4. No flame rating on an outdoor or enclosed TIM
Fix — specify a UL 94–listed grade per TDS where the enclosure requires it.
5. Hand-placed TIMs with inconsistent coverage
Fix — deliver kiss-cut TIM kits placed to the drawing so every unit gets the same interface.
Specification Tools
Two tools to take you from "this interface runs hot" to here's the family for the drawing note: a three-question TIM duty selector, and a side-by-side comparison of every family on this page.
1. TIM duty selector: three questions, one family
Answer the three questions that sort almost every server and network TIM decision. The selector returns the candidate family, the data to read on the TDS, and what to send with the drawing. The default answers below are pre-set for a typical ASIC-to-heat-sink interface; every family also appears in the material reference section, so nothing here exists only behind a script.
Candidate family: Gap Pad® TGP conformable gap fillers
A non-isolated interface across a real tolerance stack in a conditioned space is the classic gap-filler duty: pick the thickness class from the worst-case gap stack-up, the firmness from the clamp force, and the conductivity class from the heat flux. Read thermal impedance per ASTM D5470 at your assembly's pressure on the maker TDS.
2. Side-by-side: TIM family comparison matrix
Every family called out on this page, with construction, the property that drives its selection, the methods its TDS cites, and the job it serves. Click a column header to sort. Click any material name to jump to its accordion entry.
| Material | Construction | Selection driver | Methods on the TDS / by designation | Job on this page | |
|---|---|---|---|---|---|
| The interface set (vertical heat path) | |||||
| Gap Pad® TGP 1000VOUSUltra-soft viscoelastic | Filled silicone filler | Low clamp force, fragile packages | ASTM D5470 (pressure-stated) | Compute gap pads | |
| Gap Pad® TGP 1500Un-reinforced general duty | Filled silicone filler | Thickness class to gap stack-up | ASTM D5470 (pressure-stated) | Compute gap pads | |
| Gap Pad® TGP 3000 / 5000Soft S-class reinforced | Filled silicone filler | Conductivity class climbs | ASTM D5470 (pressure-stated) | Compute & radio gaps | |
| HITHERM™ HT-1205 / 1210 / 1220Thin flexible graphite | Natural-graphite sheet | Low impedance at low pressure | ASTM D5470 (pressure-stated) | Optics-cage TIM | |
| HITHERM™ HT-C3200Premium coated graphite | Coated graphite TIM | Flat, well-clamped compute joints | ASTM D5470; UL 94 V-0 per its TDS | Compute interfaces | |
| The insulating set (thermal + dielectric on one TDS) | |||||
| Sil-Pad® TSP 900 / 1600SSilicone-fiberglass insulator | Reinforced elastomer pad | Joint sits at potential | ASTM D5470 + D149 | Power shelf & radio | |
| Sil-Pad® TSP 1800ST / 3500Soft-tack / higher duty | Reinforced elastomer pad | Assembly handling, duty climbs | ASTM D5470 + D149 | Power shelf | |
| PROTECT® 1500FG + familyInsulating pad alternative | Filled insulating pad | Alternative construction / sourcing | Per vendor TDS by grade | Power shelf | |
| Spreading, attach & cushioning | |||||
| SpreaderShield™ SS / FLXNatural-graphite spreader | Graphite sheet / laminate | In-plane spreading, no height | In-plane vs through-plane per TDS | Line-card spreading | |
| SECURE® adhesive filmsHeat-carrying attach layer | Thermally conductive film | No clamp available; bond carries heat | Per vendor TDS; validate in application | Spreader attach | |
| PORON® 4701 / 4701-40V0Microcellular urethane | Microcellular PU foam | Force window over years | ASTM D3574; UL 94 V-0 (40V0 TDS) | Shelf cushioning | |
3. TIM thermal-resistance & junction-rise calculator
Enter the dissipated power, the contact area, a candidate thermal conductivity, and the bond-line thickness, and the tool returns the TIM's thermal impedance two ways — °C/W for the joint and °C·cm²/W for the ASTM D5470 area-specific framing — plus the temperature rise across the TIM. It then steers you to a candidate family by the computed impedance.
The charts redraw live: thinner bond lines and higher conductivity both lower the impedance. Use a conductivity value from the maker TDS for the grade you are considering; this tool sorts families and screens magnitudes, not grades.
Holding k and A fixed, thermal impedance falls linearly as the bond line gets thinner. The amber marker is your current input.
Material reference
Detailed specs for the families referenced on this page: the interface set (eGRAF® HITHERM™ graphite TIM, Gap Pad® TGP gap fillers, Sil-Pad® TSP and PROTECT® insulating pads), the spreading set (SpreaderShield™ natural graphite with SECURE® attach films), and the cushioning layer (PORON® 4701 series).
Values are per the maker TDS on file for each grade with the method named; equipment frameworks are cited by designation only, with the evaluation belonging to the maker's tested design. H-O die-cuts, kiss-cuts, slits, laminates, and kits every family to drawing.
eGRAF® HITHERM™ Flexible Graphite TIM (HT-1205 / HT-1210 / HT-1220 / HT-C3200)Optics-cage and compute interfaces · ASTM D5470 impedance per TDS · V-0 class on HT-C3200 per its TDS
Read impedance at your assembly's pressure: D5470 data is pressure-dependent, and riding heat sinks clamp far below the highest TDS test point.
SpreaderShield™ Natural Graphite Heat Spreaders (SS350–SS600, FLX laminates)Line-card and FPGA hot-spot spreading · strongly in-plane conductivity per TDS
Specify both conductivity directions and the attach method. A spreader bonded with the wrong attach layer loses at the interface what it gained in-plane; adhesive selection is validated in the application.
Gap Pad® TGP Conformable Gap Fillers (TGP 1000VOUS / 1500 / 3000 / 5000)CPU/GPU/ASIC tolerance stacks · thickness and conductivity classes · ASTM D5470 per TDS
Send the gap stack-up, not just the nominal gap: the worst-case thin and thick corners decide the thickness class and firmness, and an over-compressed pad loads die corners.
Sil-Pad® TSP Reinforced Insulating TIM (TSP 900 / 1600S / 1800ST / 3500)Power-shelf and outdoor device interfaces · D5470 thermal + D149 dielectric on one TDS
If the print carries a test voltage, put it on the RFQ: the dielectric requirement picks the grade as often as the thermal one does.
PROTECT® Insulating Pads + SECURE® Thermally Conductive Adhesive FilmsAlternative insulating-TIM constructions and heat-carrying attach layers · per vendor TDS
Adhesive performance depends on substrate, surface energy, temperature, exposure, dwell time, applied pressure, surface preparation, part geometry, and assembly method; final adhesive selection should be validated in the application.
PORON® Industrial Microcellular Urethane (4701 Series, 4701-40V0)Shelf cushioning, fan-tray pads, module interfaces · ASTM D3574 methods · V-0 class on the 40V0 TDS
Specify the force window and deflection, not just thickness; compression-set resistance is what keeps that spec alive over the equipment's life.
Server & network TIMs: engineer-grade FAQ
Ten of the questions we hear most from server, switch, optics, and radio-unit teams. If your question isn't here, send a drawing or call, engineering picks up.
Are these TIM pads NEBS or GR-487 certified?
No material is, and the framing matters: Telcordia frameworks such as GR-487 (equipment cabinets) and GR-3108 (network equipment in the outside plant) evaluate equipment and enclosures, so the evaluation belongs to the maker's tested design.
The materials on this page carry their own documentation: TDS values with the method named (thermal impedance per ASTM D5470, dielectric per D149), UL 94 classes on the listed grades, and lot-code traceability. They support designs evaluated to those frameworks; H-O supplies the converted parts and the paperwork, and the equipment designer owns the evaluation. [3]
Thermal conductivity or thermal impedance: which number do I design to?
Impedance. Conductivity (W/m·K) is a bulk material property; impedance (°C·cm²/W per ASTM D5470) is what the assembled joint actually sees, because it folds in thickness and the contact resistance at both faces, and it changes with clamping pressure. Two pads with identical conductivity can differ meaningfully in impedance at your pressure. Read the D5470 curve on the TDS at the pressure your assembly applies; that is the number the junction temperature answers to. [1]
How do I pick gap pad thickness and firmness for a CPU, GPU, or ASIC?
Work the tolerance stack first: package height variation, board bow, sink flatness, and clamp travel give a worst-case thin and thick corner. Pick the thickness class so the pad stays inside its TDS compression range at both corners, then pick firmness from the available clamp force, ultra-soft viscoelastic grades like TGP 1000VOUS where force is scarce or packages are fragile. Only then optimize the conductivity class.
A pad outside its compression range either lifts the sink or loads the die corners, and either failure costs more than a conductivity step.
What TIM goes between a QSFP/OSFP module and its riding heat sink?
Most designs land on thin flexible graphite (HITHERM™ HT-1205-class designations), kiss-cut to the cage window: it delivers low impedance at the riding sink's modest spring pressure, tolerates module insertion cycles, and has no grease to pump out between service events. Where the cage design prefers conformability, a thin soft gap-filler class steps in. Either way the parts are small and high-count, so they run as kiss-cut arrays on liner with placement tabs for production peel-and-place.
When is graphite the right TIM, and when is it the wrong one?
Right for thin, flat, well-clamped joints that want low impedance without pump-out or cure: optics cages, compute interfaces, spreader-to-wall landings. Wrong wherever the joint must also insulate electrically, because graphite conducts; that duty belongs to the insulating pad class (Sil-Pad® TSP, PROTECT®), whose TDSs carry D5470 thermal and D149 dielectric data on the same sheet. It is also the wrong tool for large gaps and tolerance stacks, which are gap-filler territory.
How do I know whether an interface needs an electrically insulating TIM?
Ask whether the two mating surfaces sit at different potentials or whether the print carries a test voltage across the joint. Device tabs at bus potential against a grounded sink, rectifier modules on power shelves, and PA devices on radio castings commonly do; a grounded ASIC lid against a grounded sink commonly does not. If the answer is yes, stay in the insulating pad class and put the required test voltage on the RFQ: the dielectric requirement picks the grade as often as the thermal one. [5]
Does outdoor RRH / O-RAN service change the TIM choice?
It changes the priorities. The thermal physics is the same, but the material must hold its properties across wide thermal cycling and years of unattended clamped service, which favors silicone-based pad classes with wide TDS temperature ranges (roughly -60 to +180/200 °C by grade) over anything that dries, creeps, or needs maintenance.
The enclosure's weather story belongs to the enclosure: outside-plant frameworks such as GR-487 and GR-3108 are cited by designation, the evaluation belongs to the maker's tested design, and final material selection should be validated in the application. [4]
Can H-O supply the whole board's TIM set as one kiss-cut kit?
Yes: gap pads, graphite pieces, insulating pads, spreaders, and cushioning parts can ship kiss-cut on one liner in assembly order, with peel tabs sized for gloved hands, or as labeled kit bags per unit built. Kits carry lot-code TDS records per material, which is the documentation trail an equipment evaluation wants to see, and kitting typically removes more assembly cost than any single material substitution.
Our drawing calls out a specific vendor grade. Can H-O convert it?
Usually, yes. H-O converts named grades to drawing across the graphite, gap-filler, insulating-pad, spreader, and adhesive-film families on this page, working from the vendor TDS on file. Where a called-out grade has long lead times or a closer-fit sibling exists, engineering flags the alternative with its TDS for your review; the substitution decision stays with your design team, and final material selection should be validated in the application.
What should I put on the drawing set so the quote comes back right the first time?
By job: for compute gap pads, the gap stack-up, clamp pressure, and conductivity class; for optics, the cage window geometry, spring force, and thickness budget; for spreading, the hot-spot map and exit path; for insulating interfaces, the package style, torque, and any test voltage; for outdoor radios, the casting drawing, exposure assumptions, and the framework the enclosure is evaluated to (by designation).
Plus quantities for prototype and production, and liner and kitting preferences. "Recommend the stack" is a valid callout: that is what the engineering review is for.
Glossary: terms used on this page
Quick reference for the thermal-interface terminology used throughout. Each entry links to the relevant standard or test method where applicable.
Thermal interface material (TIM)
The compliant layer that replaces air in a clamped thermal joint: graphite where isolation is handled elsewhere, gap fillers across tolerance stacks, insulating pads where the layer must also block current. Impedance per ASTM D5470 [1], pressure-dependent.
Thermal impedance vs thermal conductivity
Conductivity is the bulk property (W/m·K); impedance (°C·cm²/W) is the assembled joint's number, folding in thickness and both contact resistances at a stated pressure. Design to impedance at your pressure; compare materials by conductivity only within a thickness class.
ASTM D5470
The standard test method for thermal transmission properties of thin thermally conductive solid materials: the method behind the impedance values on TIM TDSs. Results are stated at test pressures; the value at your assembly's pressure is the one that matters. [1]
Gap filler
A conformable filled-elastomer TIM (the Gap Pad® TGP family here) specified by thickness class, firmness, and conductivity class, built to absorb real tolerance stacks between components and a common cold surface.
Heat spreader (in-plane vs through-plane)
A sheet that moves heat laterally from a hot spot to a rejection surface. Natural graphite's in-plane conductivity exceeds its through-plane value by an order of magnitude, which is the property SpreaderShield™ parts exploit; both directions are stated on the TDS.
Insulating (dielectric) TIM
ASTM D149
The standard test method for dielectric breakdown voltage and dielectric strength of solid electrical insulating materials: the method behind the dielectric values on insulating-TIM TDSs. [5]
Riding heat sink
The spring-loaded heat sink on a pluggable-optics cage that presses onto each QSFP/OSFP module through a window. Its modest spring force and the module's insertion cycles are why thin graphite dominates this interface.
Kiss-cut on liner
A cut that goes through the material but not its release liner, so parts ship as peel-and-place arrays or in-order kits. The production-line format for high-count TIM parts; tabs and assembly-order layout come off your build sequence.
Compression force deflection (CFD)
The pressure a cellular material exerts at a given compression, reported per ASTM D3574 [6] on PORON® TDSs. The number behind cushioning pads that must hold a force window for years without taking a set.
Telcordia GR-487 / GR-3108 (by designation)
Generic-requirements documents for electronic equipment cabinets (GR-487 [3]) and network equipment in the outside plant (GR-3108 [4]). They evaluate equipment and enclosures, not component materials; on this page they are cited by designation, and the materials support designs evaluated to them.
Last updated · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).
Standards, test methods & technical references
The standards, test methods, and maker technical data sheets cited throughout this page, by name and designation. Equipment frameworks are cited by designation: they evaluate equipment and enclosures, and the evaluation belongs to the maker's tested design. Standards editions current as of June 2026; verify against the publishing body before final spec. H-O converts materials tested to the material-level methods on the source maker's TDS; H-O does not certify systems or independently certify materials unless explicitly stated on the quote.
[1] ASTM D5470
Standard Test Method for Thermal Transmission Properties of Thermally Conductive Electrical Insulation Materials, published by ASTM International. The method behind the thermal-impedance values on the TIM TDSs cited across this page; results are pressure-dependent and stated at test pressures.
[2] UL 94 (material classes per grade TDSs)
Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances, published by UL. Flammability classes (including V-0) belong to the listed material grades per their TDSs, such as HT-C3200 and PORON® 4701-40V0; materials are available with UL 94 ratings per vendor TDS.
[3] Telcordia GR-487 (by designation)
Generic Requirements for Electronic Equipment Cabinets, published by Telcordia (Ericsson). Cited by designation as the framework outdoor enclosure designs are commonly evaluated to; the evaluation belongs to the equipment maker's tested design, and the materials on this page support designs evaluated to it.
[4] Telcordia GR-3108 (by designation)
Generic Requirements for Network Equipment in the Outside Plant, published by Telcordia (Ericsson), with its operating-class framework for unconditioned environments. Cited by designation as design context for RRH/O-RAN thermal interfaces; the evaluation belongs to the tested equipment.
[5] ASTM D149
Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commercial Power Frequencies, published by ASTM International. The method behind the dielectric values on insulating-TIM TDSs (Sil-Pad® TSP, PROTECT® classes).
[6] ASTM D3574
Standard Test Methods for Flexible Cellular Materials, published by ASTM International. The methods behind the compression-force-deflection and compression-set data on PORON® 4701-series TDSs used for shelf cushioning and fan-tray pads.
Updated . Standards editions current at publication; verify against the publishing body before final spec. H-O converts materials tested to the methods cited; H-O does not certify systems. Lot-specific documentation available on request.
Get a thermal-interface materials engineering quote
Send a drawing set, BOM, or board spec. We typically respond within one business day with a material recommendation, prototype lead time, and TDS verification against your gap stack-ups, clamping pressures, isolation requirements, and standards language.
See also: related H-O application pages
Engineering content for the adjacent thermal and data-center sub-applications, the parent application hub, and the owning industry hub. Each page covers material selection, failure modes, and converter-side process detail for its application family.
One drawing starts the program
Gap pads, optics TIMs, spreaders, insulating pads, or the whole kit on one liner: send the drawing and get an engineering review, a manufacturable option, and the TDS within about one business day.
Material data & standards. All thermal, dielectric, compression, and temperature values on this page are taken from the source maker's technical data sheets with the method named (ASTM D5470 thermal impedance, pressure-dependent; D149 dielectric breakdown; D3574 cellular methods; UL 94 classes per the listed grade TDSs).
Equipment frameworks (Telcordia GR-487, GR-3108) are cited by designation only: they evaluate equipment and enclosures, the evaluation belongs to the maker's tested design, and the materials on this page support designs evaluated to them.
Adhesive and PSA performance depends on substrate, surface energy, temperature, exposure, dwell time, applied pressure, surface preparation, part geometry, and assembly method. H-O converts materials; H-O does not design equipment or certify systems, and does not independently certify materials against the standards unless explicitly stated on the quote. Verify against the maker TDS, and validate final material selection in the application.
Conversion scope. H-O and converts sheet and roll stock to drawing in Winsted, Connecticut: die-cut and kiss-cut pads and arrays, slit roll widths, laminated PSA constructions, and kitted TIM sets, with material traceability and lot-code TDS records. H-O does not mold or extrude in-house; molded or extruded profiles are coordinated through a partner network. Lead-time and MOQ details are in the process strip and the quote form above.