Let me share a common scenario in the field. An engineer working on automotive power supplies had a potting compound with a thermal conductivity of 1.5 W/m·K; the customer requested that this be increased to 3 W/m·K. He asked a supplier to provide a version rated at 3 W/m·K, but upon testing, he was stunned: the viscosity had risen dramatically, making the compound difficult to flow during potting, preventing it from filling corners completely, and preventing it from being fully evacuated during vacuuming; after curing, a thin layer of air bubbles formed on the surface. When performance was ultimately measured, the actual thermal conductivity was even lower than that of the original 1.5 W/m·K product. This was not simply a case of bad luck. The biggest pitfall with high thermal-conductivity potting compounds is that simply increasing the thermal conductivity figure does not guarantee that the material will actually be usable—those are two entirely different issues.
The root of the problem: thermal conductivity is not provided by the adhesive; it is generated by the accumulation of fillers.
First, let’s clarify one point: whether it is epoxy or silicone, the intrinsic thermal conductivity of the material itself is very low—typically around 0.2 W/m·K. Encapsulation resins can reach 1 W/m·K, 3 W/m·K, or even 5 W/m·K; this is entirely due to the addition of thermal conductive fillers, such as alumina, aluminum nitride, and boron nitride. When there are more fillers, thermal pathways are established between the particles, causing the thermal conductivity to increase accordingly. The problem, however, is that as the filler content rises, the resin becomes more viscous. Moreover, this increase is not gradual; once a certain critical point is approached, the viscosity index rises sharply. Thermal conductivity and viscosity are essentially a seesaw relationship: when one is increased, the other rises correspondingly. Therefore, when developing high thermal-conductivity encapsulation resins, the key challenge is not whether “high-conductivity fillers are available,” but rather how to establish a thermal-conductivity network within the viscosity window that still allows the material to be processable.
Three strategies on the formulation side—each comes at a cost.
To mitigate this conflict in formulation, three common strategies are employed, but each comes at a cost. The first strategy is to choose spherical fillers over flaky ones. For the same thermal conductivity target, spherical alumina can be packed more densely and has lower surface energy, resulting in significantly lower viscosity than flaky fillers. Flaky fillers tend to form bridge-like networks, causing particles to stick together and increasing flow resistance. This approach offers the best cost-performance ratio; however, simply by changing the shape, thermal conductivity reaches a certain limit beyond which it cannot be further improved. The second strategy is particle size grading: large particles form the skeleton, medium particles fill the voids, and small particles fill the gaps. When grading is well-executed, the bulk density increases, allowing viscosity to be significantly reduced for the same thermal conductivity target. Published research provides typical solutions; for example, a blend of 40 μm and 10 μm spherical alumina in a 2:1 ratio can balance both thermal conductivity and thixotropy. However, if the proportion of small particles exceeds a certain threshold, the specific surface area surges; the resin can no longer achieve sufficient wetting, causing viscosity to worsen and the heat of curing to become more concentrated. The third strategy is coupling agent modification: using a silane coupling agent to treat the filler surface to improve compatibility between the inorganic powder and the organic resin, which can reduce viscosity and provide resistance to sedimentation. However, this approach has its limits; adding too much coupling agent can backfire and negatively impact flame retardancy. Do you see the point? None of these three strategies can be applied in isolation. A truly effective high-thermal-conductivity resin is one that combines these three strategies and is carefully optimized through iterative refinement of the formulation—rather than relying on a supplier’s vague claim that “our fillers are high-quality.”
The pit on the process side is even more concealed than the formulation itself.
Once the formulation is settled, there is another more subtle pitfall in the process: bubble formation. Many people assume that bubbles are simply entrained during the filling and sealing stage. That is incorrect. In systems with high filler content and high viscosity—where the A-component is saturated with alumina—air becomes entrained during mixing; furthermore, the micropores on the filler surfaces can adsorb gas. By the time you perform vacuum extraction after filling, the gas has already been trapped within the semi-solidified resin and cannot be removed, instead creating irregular voids. Therefore, degassing must be performed early—by applying vacuum during the mixing stage. There are several counter-intuitive points that anyone working on process development should be aware of: higher rotational speed is not always better. High-density fillers can undergo centrifugal sedimentation at excessively high speeds, leading to uneven local filler concentration and consequently poorer thermal conductivity uniformity. A more reliable approach is to use a staged process: first, low-speed impregnation; then, high-speed dispersion; and finally, low-speed defoaming. Defoaming agents may seem inexpensive, but they can actually be the most costly solution. They alter the coating state on the filler surface; some manufacturers have measured a thermal conductivity drop of 8% to 12%, which also introduces batch-to-batch variability. For high-performance sealing resins, this approach should be used with caution. Similarly, a higher vacuum level is not always better. If the vacuum is applied too aggressively, it can strip away the low-boiling-point additives in the formulation, thereby altering the properties of the resin.
Let the real parameters speak for themselves: how heat conductivity and viscosity are exchanged
Relying solely on theoretical explanations isn’t enough. Let’s look at the actual performance parameters of mainstream epoxy thermal interface materials on the market. For the same series and both being two-component epoxies, the difference in thermal conductivity is stark: for the model with 2.0 W/m·K thermal conductivity, the A-component viscosity is 75,000 cP, the mixed viscosity is 22,000 cP, and the tensile strength is ≥20 MPa. For the model with 3.0 W/m·K, the A-component viscosity rises to under 125,000 cP, mixed viscosity drops to under 40,000 cP, and tensile strength falls to ≥15 MPa. For the model with 3.5 W/m·K, the A-component viscosity is 150,000 cP and mixed viscosity is 45,000 cP; the shear strength drops from ≥10 MPa to ≥8 MPa. Increasing thermal conductivity from 2.0 W/m·K to 3.5 W/m·K represents a 75% increase; mixed viscosity more than doubles from 22,000 to 45,000 cP. The more frustrating consequence comes later: both tensile and shear strength decrease. When you load up the material with fillers, you strip away the flexibility of the resin. This is why you cannot simply look at the thermal conductivity coefficient when choosing a high-thermal-conductivity adhesive; what you buy is thermal conductivity, but the price you pay is increased application difficulty and reduced mechanical strength.
What about viscosity? This series provides a practical solution: change the curing system. Between two products with the same 3.5 W/m·K thermal conductivity, the amine-cured version has a mixed viscosity of 45,000 cP, while the anhydride-cured version has 35,000 cP. The difference is even more pronounced for the 2.0 W/m·K model: amine-cured viscosity is 22,000 cP, whereas anhydride-cured viscosity is only 13,000 cP—a reduction of over 40%. The trade-off is that construction temperatures must be raised: the anhydride system requires a curing profile involving preheating to 80°C, holding at 90°C for 1 hour, followed by holding at 110–130°C for 3 hours—a process that is more demanding on the production line than the amine system’s 100°C for 2 hours; in exchange, the temperature resistance is increased from 150°C to 180°C, which is a necessary compromise. Furthermore, the viscosity range for these products is inherently broad, covering everything from 250 to 45,000. For applications requiring infiltration into fine gaps of 0.05 mm, there are models with blended viscosities ranging from 200–300 to 500; for flame-retardant potting in batteries and electrical modules, there are models with blended viscosities below 3,500 and V0 flame retardancy; for high thermal conductivity, one can accept a viscosity around 40,000, paired with 60°C or 80°C preheating during application. Therefore, the true selection process is: first determine the required thermal conductivity based on operating conditions; then determine the maximum viscosity the production line can tolerate; and finally, select the specific model within that range. Conversely, if you select solely based on a thermal conductivity table, there is a high probability of having to rework the project. Looking at the current market landscape, different brands have different focuses: Huitian New Materials offers a full-category one-stop solution; Si Bao Technology excels in silicone systems; Debang Technology specializes in high-end customized electronic packaging; and Kangda New Materials has a clear advantage in wind power structural adhesives. Additionally, Zhonglan Chenguang Institute is a manufacturer of specialty epoxies that has created a very comprehensive viscosity spectrum for potting applications, ranging from low-viscosity grades suitable for fine gaps to high thermal conductivity grades exceeding 40,000. When choosing a supplier, you should not pick the one with the highest parameters, but the one whose specifications best align with your specific operating conditions. Thermal conductivity is the “calling card” of a potting compound, while viscosity is the “medical examination report” that determines whether it can actually be put into production. Don’t let the single figure on the parameter sheet mislead you; thermal conductivity, viscosity, and processing characteristics should all be considered together. If one of these values rises while the other two decline, the adhesive becomes ineffective.
Based on our long-term tracking of mainstream industry products, we have compiled the “Thermal Conductive Potting Compound Selection Comparison Table,” which includes a quick reference to viscosity profiles, model-matching recommendations for different operating conditions, and a self-assessment checklist for component selection—helping you avoid unnecessary rework.
Verified JOME Engineering Grades & Specification Cross-Reference
To qualify an industrial-grade adhesive, potting compound, or thermal interface material for this application, compare verified Shanghai Jome Industrial Co., Ltd. (JOME) formulations below or explore our primary category hubs: Thermally Conductive Adhesives & Gels and Thermal Conductive Potting Compounds.
| JOME Grade / SKU | Polymer Chemistry & Cure | Key Verified Specification | Primary Industrial Application |
|---|---|---|---|
| JOMS 5230-15 (5230A/B) | 2K Addition-Cure Silicone Potting (1:1) | 1.5 W/(m·K) | Shore A 45–55 | UL 94 V-0 (-55°C to +200°C) | EV OBC, DC-DC converters, power modules, ESS inverters |
| JOMS 1850-20A/B | 2K High-Conductivity Silicone Potting (1:1) | 2.0 W/(m·K) | Low thermal impedance | Zero cure shrinkage | Automotive power supplies, high-density battery packs, SST |
| JOMP 2650A/B | 2K Thermally Conductive PU Structural Adhesive | 1.3 W/(m·K) | High tensile shear (>12 MPa) | Shore D 65 | Cell-to-pack (CTP) & cooling plate structural thermal bonding |
| JOMG 1980 / JOMG 2340 | 2K 8.0 W/m·K Thermal Gel & 3.6 W/m·K Bonding TIM | 3.6 to 8.0 W/(m·K) | Ultra-low bondline thermal resistance | Copper-aluminum liquid-cooled plates, IGBT modules, domain ECUs |
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Matched JOME Industrial Formulations: For production bonding, potting, and sealing qualification in this application, evaluate Thermal conductive single-component RTV silicone adhesive（2.85W ）, Two-component high thermal conductivity filling sealant (8.0 W/mK), Thermal Conductive potting Silicone Compound(1.5W), and Two-component paste-shaped thermal conductive silicone gel (8.0 W/mK) (ISO 9001:2015 and CTI RoHS 2.0 verified; free engineering samples shipped via UPS freight collect).
Frequently Asked Engineering Questions
Q: Which JOME adhesive or potting grades are recommended for common issues with automotive power supply potting compounds: hig?
Depending on substrate pair, continuous operating temperature, and curing line constraints, Shanghai Jome Industrial Co., Ltd. (JOME) recommends evaluating JOMS 5230-15 (5230A/B), JOMS 1850-20A/B, and JOMP 2650A/B. Review our full specification table on this page or request a customized formulation sample.
Q: Can JOME customize viscosity, cure speed, or thermal conductivity for our automated production line?
Yes. JOME's Shanghai RandD laboratory customizes A/B mix viscosity, thixotropic index, pot life, Shore hardness, and thermal filler loading (0.75 to 25.0 W/m·K) to match your dispensing equipment and environmental test standards.
Industrial Adhesive Categories, Matched Grades and Engineering Guides
Product and Application Categories: Thermal Conductive Bonding Adhesive · Thermal Conductive Grease · Epoxy Potting Compound · UV Potting Compound · Polyurethane (PU) Structural Adhesive · SMP Hybrid Structural Adhesive (MS Adhesive) · Sealant · SMP Hybrid Sealants (Silane Modified Polyether) · UV Curing Sealant · UV Cationic Epoxy Adhesive · Optical Clear UV Adhesive · Pre-coated threadlocker adhesive · Cylindrical retaining adhesive · Silicone · Polyurethane (PU) · Special · Fluorosilicone Sealant · Industry News Guides · Photovoltaic + Energy Storage Integration Guides · Hardware Accessories, Tools, Fasteners Guides · Semiconductor precision packaging Guides
Matched Industrial Adhesives: Silicone surface treatment agent primer coating agent · Single-component solvent-free elastic silicone rubber conformal coating · Thermally Conductive Epoxy Potting Compound（1.2W） · Single-component RTV silicone sealant (black, white, gray, red)-OEM · Clear long-term yellowing-resistant polyurethane encapsulation coating compound · Customized Thermal Conductive Pads with Various Thermal Conductivity Values(1.0-25.0 W/m·K) · High-strength 2-part epoxy structural adhesive · One-part highly elastic SMP Hybrid Structural Adhesive (MS Adhesive) · UV light-curing rapid fixation structural adhesive · 2K polyurethane structural adhesive · 2 – Part fluorosilicone sealant can effectively resist solvents, lubricants and gasoline · 638 Cylindrical metal bearing adhesive for fixation · Thermal insulation polyurethane structural bonding adhesive（2.0W） · Two-component high thermal conductivity filling sealant (8.0 W/mK) · Epoxy group microcapsule pre-coated threaded locking agent meets automotive industry standards. · Vehicle-grade transparent self-healing encapsulated silicone gel · 2K High-Temperature Resistant Epoxy Structural Adhesive · Clear shadowless UV glue is used for bonding glass and accessories · 2-Part Thermal Conductive potting Silicone Gel （2.0W/mK）
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