The Surface Problem That Thermal Interface Material Putty Solves
Every engineered surface looks smooth to the naked eye. Under a microscope, it's a different story: a landscape of peaks, valleys, and microscopic voids that prevent two mating surfaces from ever achieving true full-contact. This is the problem that thermal interface materials exist to solve.
When two surfaces — say, a power module and a heat spreader — are bolted together without a TIM, the actual contact area may be a fraction of the nominal interface area. Air fills the gaps, and air is a notoriously poor conductor of heat. The result is thermal resistance that limits performance and reliability, especially in environments where heat dissipation is already a battle.
Thermal interface materials bridge that gap. The question is which type of TIM does it most effectively for your application — and in aerospace, the answer is often a putty.
Why Rigid Thermal Pads Fall Short in Extreme Aerospace Environments
Rigid thermal pads (typically silicone rubber sheets with thermally conductive fillers) perform well in many applications. They're easy to handle, dimensionally stable, and compatible with most manufacturing processes. For lower-power electronics or applications with minimal surface variation, they're often the right call.
Aerospace is a different environment. Thermal demands are higher, weight budgets are tighter, and performance margins are narrower. When a satellite is managing heat in the vacuum of space or an avionics system is cycling through extreme temperature swings, engineers need every watt of thermal performance they can extract.
Rigid pads are limited by their inability to fully conform. Even a high-quality pad leaves some air gaps at the interface. Those gaps add thermal resistance, and in aerospace applications, that resistance adds up.
How Thermal Putty Closes the Gap (Pun Intended)
Putty-based thermal interface materials are formulated to flow under contact pressure, conforming to the microscopic topography of both mating surfaces. When a putty TIM is installed and compressed, it fills the surface voids, displacing air and creating near-complete interfacial contact.
The result is a significantly lower thermal resistance at the interface. More surface contact means more efficient energy transfer, whether you're conducting heat away from a processor or spreading thermal load across a structural panel. In an environment where engineers are already squeezing every bit of performance out of a constrained thermal budget, that improvement matters.
The tradeoff is manufacturability. Putty doesn't behave like a rigid material. Every step of the production process requires techniques specifically designed to account for its deformable nature:
- Cutting: Only CNC knife cutting is viable — die cutting deforms edges, waterjet degrades the material.
- Handling: Liner swap protocols and careful operator technique are required to move parts without permanent deformation.
- Inspection: Standard fixturing can't grip the part without changing its geometry — inspection setups must be non-contact or specially designed.
- Shipping: Custom spacer packaging is needed to survive carrier-induced drop and vibration loads without deforming the finished geometry.
- Installation: The liner is removed only at the point of installation, and the part must be registered accurately before contact pressure is applied.
Essential Background Reading:
- Thermal Management Applications: Overview of thermal management capabilities, materials, and manufacturing processes available for aerospace and defense applications.
- Thermal Interface Materials: Making the Right Choice for Your Application: Dispensed solutions vs. pre-cut pads — performance trade-offs, volume economics, and application context that frames TIM selection decisions.
- Custom Gasket Cutting Methods — Die Cutting vs. Waterjet vs. Digital Cutting: How each converting process works and where each breaks down — essential context before exploring putty-specific manufacturing constraints.
- Aerospace & Defense Manufacturing: AS9100, ITAR, and CMMC-compliant manufacturing for programs where thermal performance and schedule compliance aren't optional.
Conductive Silicone Filler Materials: Silver, Copper, and Aluminum
Electrically conductive silicones used in aerospace thermal and EMI applications are distinguished primarily by their filler material. The filler determines both the thermal and electrical conductivity of the compound, and the choice has real implications for performance and cost.
The three dominant filler metals in aerospace applications each bring a different value proposition to the table.
Filler Material | Thermal Conductivity | Electrical Conductivity | Relative Cost | Primary Use Case |
Silver | Excellent | Excellent | High | High-performance EMI and thermal applications |
Copper | Very Good | Very Good | Moderate | Thermal pads requiring strong conductivity at lower cost than silver |
Aluminum | Good | Good | Low | Cost-sensitive applications where performance tradeoffs are acceptable |
Silver-Filled Silicone Thermal Pads
Silver is the premium filler material in this class of compounds. It delivers the highest conductivity values for both heat and electricity, making it the material of choice in applications where performance is the primary driver and cost is secondary. Silver-filled silicones appear frequently in mission-critical electronics shielding and high-power thermal applications where no performance tradeoff is acceptable.
Copper-Filled Silicone Thermal Pads
Copper-filled silicones occupy the middle ground, performance close to silver at a meaningfully lower material cost. Copper's thermal and electrical conductivity are excellent, and it's widely used in aerospace thermal pads where performance requirements are high but the cost premium of silver is difficult to justify in the BOM.
Aluminum-Filled Silicone Thermal Interface Material
Aluminum is the cost-effective filler for applications where good conductivity is required but premium performance is not. Aluminum-filled compounds are lighter than their silver and copper counterparts, a meaningful advantage when weight is a constraint. The conductivity values are lower, but for many aerospace thermal applications, they remain more than sufficient.
The specific filler selection ultimately depends on the customer's design requirements, performance targets, and cost constraints. A materials engineer evaluating TIM options should involve their manufacturing partner early in the process. Filler selection affects not only performance but also the manufacturing processes available, the handling requirements, and the tolerance achievable in production.
Related Content:
- Precision Die-Cut Thermal Interface Materials: When Standard Solutions Aren't Enough: When solid conductive silicone pads can be die cut to tight tolerances — and when putty's properties make that process impossible.
- Thermally Conductive Elastomers — Advanced Materials for Flexible Thermal Management: Deep-dive on thermally conductive elastomeric material categories, filler options, and selection guidance for aerospace applications.
- Thermal Contact Resistance — Engineering Solutions for Maximum Heat Transfer Efficiency: The physics behind why putty outperforms rigid pads — interfacial resistance, surface topography, and the math that makes conformance matter.
- Defense Thermal Management Components — Meeting Military Standards: MIL-SPEC requirements that govern thermal interface material selection, handling, and documentation for defense programs.
Manufacturing Aerospace Putty TIMs: Why CNC Knife Cutting Is the Only Option
The deformable nature of putty TIMs creates a hard constraint on manufacturing process selection. The three most common converting processes for flat elastomeric materials are die cutting, waterjet cutting, and CNC knife cutting (commonly referred to as Zund cutting after the Swiss machine manufacturer widely used in this application). For putty materials, only one of these processes is viable.
Why Die Cutting Doesn't Work for Thermal Putty
Die cutting applies a shaped blade under high press force to stamp out a part geometry from sheet material. The process works well for dimensionally stable materials: solid silicone rubbers, foams, adhesive films. For putty, the press force creates a problem: the blade compresses and displaces the material before it cuts, deforming the edges and producing inaccurate final dimensions. The geometry of the part is compromised before it ever leaves the press.
Die cutting is not a viable option for putty-based TIMs.
Why Waterjet Cutting Doesn't Work for Thermally Conductive Putty
Waterjet cutting uses a high-pressure stream of water, often mixed with an abrasive medium, to cut through materials with no heat-affected zone and no hard tooling requirement. It's an excellent process for precise corners, large-format parts, and materials that are difficult to cut by other means. However, water and putty TIMs are fundamentally incompatible. Water absorption alters the material properties of the compound, and exposure to a high-pressure stream will degrade the part. The process simply cannot be used.
CNC Knife Cutting: The Right Tool for Thermal Putty Manufacturing
CNC knife cutting uses a sharp oscillating or tangential blade controlled by a digital toolpath to cut parts from sheet material. Unlike die cutting, the blade path is computer-controlled and applies minimal lateral force to the surrounding material. Unlike waterjet cutting, it introduces no moisture.
For putty TIMs, CNC knife cutting is the only viable process. The blade follows the programmed geometry precisely, the material is held flat during cutting, and the resulting parts maintain dimensional accuracy. Standard tolerances for solid or dense elastomeric materials (BL2 designation) in the sub-25 mm (1.0") dimension range are ±0.38 mm (±0.015"). Tighter tolerances can be achieved through creative fixturing and toolpath strategies, but this increases lead time and cost, and should only be pursued when the design genuinely requires it.
The Liner Swap: How to Handle Thermal Interface Material You Can't Grip
Once a putty TIM is cut to its final geometry, it still needs to be transferred, inspected, installed, and in some cases shipped, all without deforming. This is where material handling protocols become as important as the manufacturing process itself.
Most putty TIM materials arrive from the supplier with a thin release liner on each face. This liner protects the material during storage and transit, but it offers almost no structural support. For small parts, it's manageable. For larger TIMs, components spanning hundreds of square millimeters or more, the thin liner is insufficient to prevent the part from sagging, stretching, or deforming during handling.
The solution is a liner swap: replacing the supplier's thin protective film with a thicker paper liner before the cutting operation begins. The thicker liner provides a rigid backer that gives operators and installers something to grip, flex, and position without making direct contact with the putty surface.
Why the Liner Swap Works
The paper liner acts as a sacrificial handling layer. It doesn't bond permanently to the putty, it's removed at the point of installation, but during the intermediate stages of cutting, inspection, and transport, it provides the structural support the material lacks on its own.
This technique allows parts to be cut on the CNC knife cutter, stripped of surrounding scrap material, inspected dimensionally, and transferred to the next operation without the deformation risk that would otherwise make large-format putty parts nearly impossible to produce consistently.
Shipping Considerations for Aerospace Putty TIMs
Large-format putty TIMs present a shipping challenge that's distinct from most converting parts. The material is susceptible to deformation under its own weight, and standard shipping packaging provides inadequate support.
Effective shipping design for putty TIMs involves custom-designed spacers that maintain the part flat and distribute any incidental contact loads across the surface uniformly. The goal is to ensure the part survives the drop, shock, and vibration conditions of transit — conditions that postal and freight carriers generate routinely — without permanent deformation to the finished geometry.
This level of packaging engineering adds a step that most converting shops don't think about. It's worth discussing proactively with any manufacturing partner handling large or complex putty TIM geometries.
Miniaturization: The Defining Challenge in Aerospace TIM Applications
Aerospace TIMs are, almost by definition, small. Weight is the dominant constraint in aircraft and spacecraft design. Every gram of unnecessary mass carries a real cost in fuel, payload capacity, or mission performance. That drives electronics packaging toward extreme miniaturization, which in turn drives TIM geometries toward features that push the limits of conventional converting processes.
Complex geometries with walls as thin as 0.51 mm (0.020"), roughly the thickness of five sheets of printer paper, are not uncommon in aerospace TIM applications. At that scale, the challenge is no longer just cutting the part accurately. It's holding the material down without compromising it, selecting the right cutting sequence to avoid damaging thin walls before they're supported, and then managing the resulting parts through inspection and installation.
When geometries push into sub-millimeter feature territory, CNC knife cutting is generally preferred for its low contact force and programmable toolpath control. The process allows the toolpath to be sequenced to cut the most structurally critical features last, reducing the risk of thin walls deflecting or tearing before the surrounding material provides support.
Frequently Asked Questions: Thermal Interface Material Putty vs. Pad for Aerospace
What is the difference between thermal interface material putty and a thermal pad?
Thermal interface material putty is a soft, deformable compound that flows under contact pressure to conform to the microscopic surface imperfections of both mating surfaces, filling air voids and minimizing interfacial thermal resistance. A rigid thermal pad is a dimensionally stable silicone rubber sheet that maintains its shape under compression. Putty achieves lower thermal resistance because it achieves near-complete interfacial contact; rigid pads leave residual air gaps at uneven surfaces. For aerospace applications with high thermal demands and tight weight budgets, putty typically outperforms rigid pads.
Can thermal putty be die cut or waterjet cut?
No. Die cutting deforms the edges of putty-based TIMs because the press force compresses and displaces the material before the blade cuts through — producing out-of-tolerance, unusable parts. Waterjet cutting introduces moisture that is absorbed by the putty compound, degrading its thermal and mechanical properties. CNC knife cutting is the only viable cutting process for thermally conductive putty materials.
What filler material should I use for an aerospace thermal pad — silver, copper, or aluminum?
Silver-filled silicone delivers the highest thermal and electrical conductivity, making it appropriate for mission-critical high-power applications where no performance tradeoff is acceptable. Copper-filled silicone offers performance close to silver at meaningfully lower material cost and is widely used when performance requirements are high but the silver cost premium is difficult to justify. Aluminum-filled silicone is the lightest and lowest-cost option, appropriate for cost-sensitive applications where good — but not premium — conductivity is acceptable. Filler selection should involve the manufacturing partner early, as it affects available processes, handling requirements, and achievable tolerances.
Why do aerospace thermal interface materials deform during manufacturing?
Putty-based TIMs are formulated to be deformable — that conformability is precisely what makes them effective at filling interfacial surface voids. The same material property that makes them thermally superior also makes them susceptible to deformation from press forces (which eliminates die cutting), moisture exposure (which eliminates waterjet cutting), direct gripping, and insufficient packaging support. Every stage of production requires handling protocols specifically designed to account for the material's lack of dimensional rigidity.
How should thermal putty liner handling be managed during aerospace TIM production?
The supplier's thin protective release liner should be replaced with a thicker paper backer before cutting begins. This liner swap gives operators a rigid handling layer that prevents sagging, stretching, or deformation during cutting, inspection, and transport. The paper liner is removed only at the point of installation. For large-format putty TIMs, custom spacer packaging is also required for shipment — standard packaging allows deformation under the part's own weight during transit.
What tolerances are achievable when CNC knife cutting thermal putty?
Standard tolerances for BL2 (solid/dense) designation elastomeric materials cut on a CNC knife cutter are ±0.38 mm (±0.015") for features under 25 mm (1.0") in dimension. Tighter tolerances are achievable through creative fixturing and toolpath strategies, but this increases both lead time and cost. Tolerances should only be tightened beyond standard when the functional design requirement genuinely demands it — not as a precautionary default.
Next Steps:
- Engineering Support & DFM Review: How Modus Advanced engineers engage early to select the right TIM, design for manufacturability, and prevent downstream handling and tolerance failures.
- The Complete Engineer's Guide to Thermal Management: The comprehensive reference covering material selection, process options, and application guidance for thermal management from prototype through production.
- Thermal Gap Pad Compression — Optimizing Performance Through Proper Selection: How compression force, thickness tolerance, and material choice interact to determine real-world thermal performance at the interface.
- Quality Management at Modus: AS9100, ISO 9001, and ITAR certifications — and the measurement technology behind them — that aerospace thermal management programs require.
Modus Advanced: Your Engineering Partner for Aerospace Thermal Management
Thermal interface material manufacturing for aerospace applications requires more than a cutting machine and a materials catalog. It requires engineering judgment at every step — process selection, liner strategy, fixturing design, handling protocol, and shipping solution — all applied to materials that actively resist being manufactured.
Modus Advanced brings engineering expertise to every stage of the production process. More than 10% of our staff are engineers, and we engage directly in the design process to help partners select the right TIM for their application, design features that are manufacturable at production volumes, and avoid the handling and tolerance problems that derail programs downstream.
Our capabilities are purpose-built for the demands of aerospace thermal management:
- CNC knife cutting: The only viable process for putty-based TIMs, with engineering-programmed toolpath sequencing for complex geometries.
- Die cutting and waterjet cutting: For dimensionally stable conductive silicone rubbers where geometry and volume favor each process.
- Thermal gel dispensing: For applications where a dispensed solution is a better fit than a cut pad.
- Assembly and installation: We install thermal pads directly onto customer hardware, managing the full handling and fixturing challenge in-house.
See It In Action:
- Space Supply Chain: Deep Materials Knowledge Under Pressure: How Modus Advanced found an alternative thermally conductive gap filler when a globally sourced material failed to arrive — and saved a flight-worthy build schedule.
- Space-Critical Components: Engineering Custom Solutions for Tight Tolerances: How Modus developed a custom converting process to achieve demanding profile tolerances on space-application components that a previous supplier couldn't deliver.
- Small Bead FIP: Breaking Process Boundaries: The Modus engineering team engineered a repeatable process for a feature size the material manufacturer had never rated — the same problem-solving applied to every challenging TIM project.
All capabilities are backed by AS9100, ISO 9001, and ITAR certifications that aerospace and defense programs demand. We support partners from prototype through production, with quote turnarounds in 48 hours or less.
When a satellite needs to shed heat in the vacuum of space, or an avionics system needs to survive years of thermal cycling, the TIM holding it all together has to perform. Partner with a manufacturing team that understands what's at stake — because one day matters.
