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Flame-Retardant Heatsink Compound for Safety-Critical Electronics — STG-716
STG-716 combines 2.2 W/m·K thermal conductivity with UL 94 V-0 flame classification — for engineers where fire-risk compliance and heat dissipation cannot be treated as separate decisions. TDS and UL cert available.
Description
Fong Yong Chemical Co., Ltd. is one of the leading manufacturers and suppliers of Flame-Retardant Heatsink Compound for Safety-Critical Electronics — STG-716 in Taiwan. Welcome to wholesale bulk customized Flame-Retardant Heatsink Compound for Safety-Critical Electronics — STG-716 at low price from our factory. If you have any enquiry about quotation and free sample, please feel free to email us.
STG-716 is a silicone-based thermally conductive grease formulated for electronic assemblies where thermal management and flame-retardant compliance must be evaluated as a single requirement rather than two independent decisions. It carries UL 94 V-0 flame classification under UL File E470964 and delivers a thermal conductivity of 2.2 W/m·K, covering the interface between heatsink and power component across an operating range of −50°C to +180°C. Unlike unfilled silicone compounds, STG-716 uses metal oxide filler to achieve both low surface tension for substrate wetting and controlled combustion behavior.
Most thermal interface material failures in safety-critical assemblies are not caused by inadequate thermal conductivity - they result from selecting a material that passes thermal validation but carries no verified flame classification, leaving the assembly exposed to a compliance gap that surfaces only during safety review. At that stage, re-specification requires re-validation of thermal performance, potentially re-running the thermal model, and re-testing the assembly. Specifying a material that carries both certifications from the outset eliminates this re-work path.
Key Takeaways
UL 94 V-0 classification is material-specific, not system-level - the flame classification applies to STG-716 in the tested configuration. Assembly design, substrate, and interface thickness should be confirmed against UL File E470964 conditions before compliance is assumed.
2.2 W/m·K is the material thermal conductivity, not the interface thermal resistance - actual thermal performance depends on bondline thickness, surface flatness, clamping force, and application method. A 50 µm bondline and a 300 µm bondline using the same material can produce substantially different junction temperatures.
STG-716 is a paste-form interface material, not a structural adhesive - it does not cure, does not bond surfaces, and should not be used as the sole mechanical retention method in any assembly.
Long-term storage may cause oil separation (bleeding) - this is a physical settling phenomenon, not degradation. Gently remixing prior to use restores dispersion and thermal properties.
When to Use
STG-716 is appropriate for assemblies where the thermal interface material is subject to safety or fire-risk review alongside thermal performance requirements. Applicable scenarios include power electronics in enclosed housings, industrial control modules, safety-rated instrumentation, and semiconductor-to-heatsink interfaces in systems that must document material flame classifications for certification purposes. Because STG-716 is a paste, it is suited to interfaces where surface geometry is not perfectly flat, where micro-scale voids would otherwise trap air and elevate contact resistance.
The −50°C to +180°C operating range makes it suitable for assemblies with wide ambient variation or high-power density components. Where curing is not possible due to temperature constraints or assembly sequence, a non-curing paste eliminates cure schedule management entirely - the material performs immediately after application and clamping.
When NOT to Use
Do not use STG-716 in fully encapsulated or potted assemblies where the encapsulant provides the primary thermal conduction path. In that configuration, the potting compound thermal resistance governs junction temperature, not the interface grease. The appropriate material for thermally critical potted assemblies is a thermally conductive potting compound - see E533/H533 for assemblies requiring both thermal conductivity and UL 94 V-0 encapsulation.
Do not use in applications where long-term serviceability is not planned and pump-out risk cannot be accepted. In assemblies undergoing repeated thermal cycling without provision for periodic grease inspection or replacement, pump-out may progressively increase contact resistance over service life. If re-servicing is not feasible, a phase-change or thermally conductive bonding material may be more appropriate depending on the application temperature range.
Do not apply with grease gun equipment before testing compatibility. Certain grease gun designs seize when used with heavily filled paste compounds. Test dispensing equipment prior to production use.
Failure Scenario
The most costly failure mode in flame-retardant thermal interface applications is not a thermal failure - it is a compliance failure that occurs after thermal validation is complete. An engineer selects a thermal grease based on conductivity and operating temperature. The thermal model is validated. The assembly passes junction temperature testing at rated power. The product then enters safety review for CE, UL, or IEC compliance. The thermal interface material has no flame classification. The assembly cannot be certified without a material change.
At that stage, re-specification requires re-validating thermal performance with the replacement material, re-running the thermal model if the new material's conductivity or viscosity differs, and in some cases re-testing the assembly. The cost is measured in engineering weeks and schedule delay, not material cost. The original thermal grease selection - made without checking for a flame classification - was never flagged because thermal grease is frequently treated as a commodity item rather than a certified component.
Figure 1. Pump-out mechanism over thermal cycling. CTE mismatch between heatsink and substrate drives cyclic lateral shear, progressively displacing grease outward. After sufficient cycles, the center of the contact area may become depleted, increasing thermal resistance without visible external failure indicators.
A second failure mode is voiding caused by surface contamination. Target surfaces that are not cleaned with solvent - or cleaned with soap and water - may retain a residue film that prevents STG-716 from fully wetting the substrate. The result is discrete contact patches rather than a continuous interface layer. Localized high-resistance zones create thermal hotspots that are not predicted by the thermal model, which assumes uniform coverage. By the time field returns identify the failure, the relationship between application process and junction temperature has rarely been investigated - contamination-related voiding goes unrecorded because the assembly appeared to pass incoming inspection.
Technical Information
STG-716 achieves a thermal conductivity of 2.2 W/m·K through metal oxide filler loading in a silicone base. The silicone carrier provides chemical stability and low surface tension, enabling the compound to wet most substrate materials - aluminum, copper, ceramics, and molded housings - without requiring surface priming. The metal oxide filler is electrically non-conductive, maintaining dielectric isolation at the interface. This matters in assemblies where heatsink and component are at different potentials: the grease acts as both thermal conductor and electrical insulator.
The penetration value of 330 × 10⁻¹ mm indicates a medium-consistency paste - viscous enough to stay in position after application but workable enough to spread under manual or tool-assisted application. Evaporation after 24 hours at 200°C is less than 1.5%, confirming thermal stability at continuous operating conditions within the rated range. This low volatile loss is relevant for enclosed assemblies where outgassing could contaminate optical components or affect contact surfaces.
RTI (Relative Thermal Index) for electrical properties is rated at 105°C under UL File E470964. This rating applies to the material's performance as an electrical insulating component at continuous service temperature. For assemblies operating at higher peak temperatures, confirm that the RTI rating corresponds to the application's continuous duty temperature - peak transient temperatures during fault conditions are outside the RTI definition.
Technical Documentation & Compliance
UL certification for STG-716 is listed under UL File E470964, covering the STG-710 through STG-719 product series. The listed flame class is UL 94 V-0. RTI electrical is rated at 105°C. The UL listing applies to silicone grease on aluminum substrate in the tested thickness range - confirm that your application configuration falls within the listed conditions before citing the certification in a compliance submission.
🔗 TDS Download - STG-716 Technical Data Sheet
🔗 UL Certificate - File E470964 (STG-710 thru STG-719)
Application Process
Surface preparation - clean with solvent, not soap or detergent. Both the heatsink surface and the component contact surface must be free of oil, dust, oxide film, and machining residue before application. Use an isopropyl alcohol or equivalent solvent and allow the surface to dry completely. Soap and detergent leave residue films that prevent full substrate wetting, producing contact voids that elevate thermal resistance. This step is not optional - surface cleanliness is the single most controllable variable affecting bondline quality.
Select application method based on required bondline consistency. STG-716 can be applied by manual spreading, screen printing, or automated dispensing equipment. Screen printing provides the most consistent bondline thickness across production volumes and is preferred where unit-to-unit thermal resistance variation must be controlled. Manual spreading is acceptable for prototype and low-volume production but introduces more operator-dependent variation. Automated syringe dispensing is suitable for defined deposit patterns but requires equipment compatibility testing with this paste grade before production use - certain dispensing nozzle geometries may seize with heavily filled compounds.
Apply the minimum layer that achieves full coverage. Because STG-716 has a thermal conductivity of 2.2 W/m·K - lower than aluminum (∼200 W/m·K) or copper (∼400 W/m·K) - a thicker grease layer increases, not decreases, total interface thermal resistance. The objective is the thinnest uniform layer that eliminates air gaps across the full contact area. Over-application is a common error: excess grease squeezed to the periphery under clamping does not improve thermal performance and may contaminate adjacent components.
Assemble under consistent, controlled clamping force. Clamping compresses the grease layer into micro-surface irregularities, displaces trapped air, and establishes the final bondline thickness. Insufficient clamping leaves voids; inconsistent clamping across production units produces unit-to-unit thermal resistance variation. After assembly, inspect for uniform squeeze-out at all edges of the contact area - asymmetric squeeze-out indicates tilt or uneven force distribution and should be investigated before the assembly is released.
If stored material shows oil separation (bleeding), gently mix before use. Separation is caused by filler settling during storage and does not indicate degradation. Remix until the paste returns to uniform consistency. Do not use separated material without remixing - localized filler-depleted zones in the paste produce low-conductivity regions in the applied layer.
Supply & Procurement Information
STG-716 is supplied in 1 kg and 10 kg containers. Shelf life is 12 months in unopened original containers stored at 25°C or lower, in a dry location away from sunlight, elevated temperature, and high humidity. Containers should be sealed immediately after use to prevent moisture ingress and surface skinning. Once opened, use promptly or reseal tightly. TDS and UL certification documentation are available for procurement qualification submissions.
FAQ
Q: What does UL 94 V-0 classification mean for a thermal grease, and why does it matter in heatsink applications?
A: UL 94 V-0 is a material-level flame classification, not a system-level approval. It indicates that the material, when tested in the specified thickness and substrate configuration, self-extinguishes within 10 seconds after two 10-second flame applications and does not produce flaming drips. For thermal interface materials used in enclosed electronic assemblies - power supplies, industrial controls, safety-rated instrumentation - this classification is relevant because the grease is positioned at or near high-energy components where a fault condition could expose the material to an ignition source. Most general-purpose thermal greases carry no flame classification. If the assembly must pass UL, CE, or IEC safety review, specifying an unclassified thermal grease can trigger a material change after thermal validation is already complete - requiring re-testing with the replacement material. STG-716 carries UL 94 V-0 under File E470964, covering the STG-710 to STG-719 series on aluminum substrate.
Q: What is the difference between thermal grease (STG-716) and thermally conductive potting compound (E533) for heat management?
A: They serve different functions in the thermal path and are not interchangeable. Thermal grease is an interface material placed between two rigid surfaces - typically a component and a heatsink - to fill micro-surface irregularities and reduce contact resistance. It does not cure, does not bond surfaces, and the assembly remains serviceable. Thermally conductive potting compound fills the entire cavity around components, provides structural encapsulation, and cures permanently. In a potted assembly, the potting compound is the dominant thermal resistance - not the component-level interface. If the potting compound has low thermal conductivity (generic epoxy: ~0.2 W/m·K), applying high-performance thermal grease at the component level does not address the bottleneck. The correct material selection depends on whether the assembly is serviceable (thermal grease) or permanently encapsulated (thermal potting compound). For UL 94 V-0 encapsulation with 1.5 W/m·K thermal conductivity, see E533/H533.
Q: How does bondline thickness affect thermal performance, and how thin should the grease layer be?
A: Thermal resistance of the grease layer is proportional to its thickness: R_th = t / (k × A), where t is bondline thickness, k is thermal conductivity (2.2 W/m·K for STG-716), and A is contact area. Doubling the bondline thickness doubles the interface thermal resistance. A 50 µm bondline over 10 cm² produces approximately 0.023 °C/W; a 300 µm bondline over the same area produces 0.136 °C/W - a 6× difference from the same material. The objective is the thinnest layer that achieves complete, void-free coverage across the full interface area. In practice, bondline thickness is controlled by surface flatness, applied clamping force, and paste viscosity - not by specifying a target thickness in isolation. For production consistency, screen printing provides more repeatable bondline control than manual spreading. Excess material squeezed out at the edges during assembly does not improve performance and should be contained to prevent contamination of adjacent components.
Q: What causes thermal grease to pump out over time, and how can it be managed?
A: Pump-out occurs when repeated thermal cycling drives lateral displacement of the grease layer. As the assembly heats and cools, the heatsink and substrate expand and contract at different rates (CTE mismatch). This cyclic shear stress at the interface causes the grease to migrate outward from the center of the contact area, progressively thinning the bondline until coverage becomes incomplete. The rate and severity of pump-out depend on CTE mismatch magnitude, temperature swing per cycle, cycling frequency, clamping force consistency, and paste viscosity. STG-716's silicone base provides reasonable resistance to pump-out under moderate cycling conditions, but no paste-form thermal interface material is immune to this mechanism at high cycle counts with large temperature swings. For assemblies with aggressive thermal cycling profiles (e.g., automotive underhood, outdoor industrial), pump-out risk should be evaluated through accelerated thermal cycling testing on the actual assembly before specification lock-in. If re-servicing is not feasible over the product's service life, a phase-change or bonding-type thermal interface material may be more appropriate depending on application constraints.
Q: Can STG-716 be used across the full −50°C to +180°C range without performance degradation?
A: The −50°C to +180°C operating range reflects the silicone base's thermal stability and low-temperature flexibility. Silicone retains workable consistency at low temperatures where hydrocarbon-based greases may stiffen significantly, and it resists thermal degradation and volatile loss at elevated temperatures - evaporation after 24 hours at 200°C is less than 1.5%. However, operating temperature range is a necessary condition for suitability, not a sufficient one. At temperatures above 150°C, the rate and extent of pump-out under thermal cycling may increase relative to ambient-temperature applications. At the lower end of the range, confirm that the paste viscosity at minimum operating temperature is compatible with the application method - very low temperatures increase paste stiffness, which may affect screen printing or dispensing behavior. The RTI electrical rating of 105°C applies to the material's continuous service as an electrical insulating component, not to its thermal conductivity performance. For applications requiring continuous service above 105°C as an insulating material, the RTI rating should be factored into the dielectric performance assessment.
Next Steps
Evaluating STG-716 for a safety-critical thermal interface application? Request a sample to validate bondline thickness, surface wetting behavior, and thermal performance under your application conditions before specification lock-in. Thermal grease performance is application-dependent - laboratory validation using your actual substrate geometry and clamping configuration is the appropriate qualification step. 🔗 Request a Sample
Need to confirm UL 94 V-0 scope for your assembly configuration? The UL listing covers specific substrate and thickness conditions. Contact our technical team to confirm that your application falls within the certified parameters and to obtain the full UL File E470964 documentation. 🔗 Request Technical Discussion
Ready to move to procurement? Pricing is available for both 1 kg and 10 kg pack sizes. Lead time and volume pricing depend on order quantity. 🔗 Request Pricing
→ Further Reading: Thermal Pad vs Thermal Paste vs Thermal Potting Compound - Engineering Selection Guide
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| Property | Value |
|---|---|
| Product Model | STG-716 |
| Material Type | Silicone-based thermally conductive grease (paste) |
| Appearance | White paste |
| Specific Gravity (25°C) | 2.6 |
| Penetration (10⁻¹ mm) | 330 |
| Thermal Conductivity (W/m·K) | 2.2 |
| Operating Temperature Range | −50°C to +180°C |
| Evaporation - 24 h at 200°C (%) | < 1.5 |
| Flame Classification | UL 94 V-0 |
| UL File Number | E470964 (STG-710 thru STG-719) |
| RTI - Electrical | 105°C |
| Electrical Properties | Dielectric insulating (non-conductive filler) |
| Corrosiveness | Non-corrosive |
| Application Methods | Manual spreading, screen printing, automated dispensing |
| Packaging | 1 kg, 10 kg |
| Shelf Life (unopened, ≤25°C) | 12 months |
All values are typical properties measured at 25°C unless otherwise stated. Final material suitability must be validated against application-specific conditions. UL certification scope should be confirmed against UL File E470964 for the applicable substrate and thickness configuration.
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