Potting compounds are essentially epoxies or specialised thermosetting materials. They are used to seal cavities in electric assemblies in order to protect them from chemical, mechanical, and thermal stressors.
Epoxy potting compounds are used across a wide range of industries, such as aerospace, electronics, and automotive, amongst others. They ensure that electrical circuits or devices continue to function at a high level even in environments that are subject to thermal cycling, vibration, and chemical spills.
At Kohesi Bond, our advanced formulations are designed to remain highly functional through the extreme working conditions of different industries. They are engineered to ensure that their characteristics of hardness, viscosity, and CTE (coefficient of thermal expansion) directly correlate with (ASTM E-595), USP Class VI biocompatibility, FDA standards, and UL flame retardancy.
The physical reaction of any potting compound to different types of stress is an important aspect of its chemical composition. This is why we consider optimising the key physical properties of our formulations to be central to our engineering philosophy.
A] Why Physical Properties Matter
Physical properties are crucial for selecting an electrical potting compound because they directly impact both the processing and long-term performance of your final product. Simply choosing a resin from a datasheet is not enough; you must ensure its physical characteristics align with your application’s specific needs.
Neglecting key physical properties can lead to significant field failures. For example, using an epoxy with an incorrect viscosity might prevent it from fully penetrating fine gaps, leaving voids that compromise electrical insulation. Similarly, an excessively rigid compound may cause stress fractures instead of preventing them. Understanding these properties is essential for maximising both safety margins and production yield rates.
- Viscosity: This property controls how easily the compound flows. A low viscosity is necessary for penetrating tight spaces and fully encapsulating complex geometries. Conversely, a higher viscosity provides better component retention and prevents dripping on vertical surfaces.
- Hardness: Hardness measures the material’s resistance to physical stress. A harder compound offers greater protection against impact and mechanical stress, while a softer, more flexible compound is better for absorbing shock and withstanding vibration. The Shore hardness scale is used to measure this property, ranging from Shore A (softer, like rubber) to Shore D (harder, like rigid plastic).
- Coefficient of Thermal Expansion (CTE): CTE measures how much a material expands and contracts with changes in temperature. Matching the compound’s CTE to the substrate’s is critical for minimising stress during thermal cycling. A mismatch can cause stress fractures and lead to delamination over time.
B] Viscosity
Definition and Measurement
Viscosity is a measure of a fluid’s resistance to flow. A low-viscosity fluid is thin and flows easily (like water), while a high-viscosity fluid is thick and flows slowly (like honey). Viscosity is a critical parameter for potting compounds and is measured in units of centipoise (cP) using a controlled viscometer. Since viscosity is highly dependent on temperature, all measurements should be performed under specific temperature conditions (typically 25°C / 77°F) to ensure consistent and reproducible results.
Relevance to the Potting Process
The viscosity of a potting compound directly impacts its ability to fill cavities and encapsulate components effectively.
- Low-Viscosity Compounds (1,500 – 3,000 cP): These fluids flow easily and are ideal for penetrating fine gaps and complex geometries. They facilitate thorough wetting and help to minimise air entrapment and voids. However, it is important to ensure that the fillers in the compound remain stable and do not settle over time.
- High-Viscosity Compounds (up to 40,000+ cP): These compounds offer greater dimensional stability and can reduce shrinkage during curing. They are less likely to slump on vertical surfaces and provide excellent component retention. High-viscosity systems often require specialised dispensing equipment to ensure consistent and accurate application.
The choice of viscosity is a key design consideration. For a successful outcome, the viscosity of the potting compound must be carefully selected to match the complexity of the PCB and the specific application method being used.
Kohesi Bond Expertise
At Kohesi Bond, we engineer our potting compounds to optimise for both manufacturing efficiency and long-term field reliability.
- Low-Viscosity Epoxies: Our low-viscosity, thermally conductive epoxies are designed for intricate PCB potting. They provide exceptional flow and penetration, enabling void-free encapsulation and full coverage of complex geometries.
- Medium- to High-Viscosity Epoxies: These formulations offer superior dimensional integrity and greater system stability during the curing process. They are ideal for applications requiring robust component retention and minimal slump.
Each compound is developed to meet the unique needs of your application, ensuring maximum performance from the moment of application through the entire service life of your product.
Optimize Your Potting Compound Selection Today
Choosing the right viscosity, hardness, and CTE is crucial for reliable electronics performance. Let our experts help you identify the ideal formulation for your application.
C] Hardness
Hardness is a measure of a cured epoxy’s resistance to permanent indentation or deformation. It’s a key property for predicting how a potting material will distribute mechanical stress. Selecting the correct hardness can prevent premature cracking, delamination, and component fatigue, ensuring long-term reliability.
Understanding Hardness: Shore A vs. Shore D
Hardness is measured using a durometer on two standardised scales:
- Shore A: This scale is used for softer, more flexible materials, such as elastomers and soft plastics. It’s ideal for quantifying materials that require a degree of pliability, like a rubber gasket.
- Shore D: This scale is for harder, more rigid materials, like hard plastics and very rigid epoxies. It measures the resistance of a material to a blunt-tipped indenter.
Epoxy potting compounds can be engineered to a wide range of hardness values, from Shore A (60–90) to Shore D (70–90), as per ASTM D2240 standards.
Application Implications
The ideal hardness depends directly on the application’s environment and performance requirements.
- Softer Materials (Shore A): These are best for environments with high vibration and thermal cycling, such as automotive modules. Their ability to absorb and dampen energy helps protect sensitive components and solder joints.
- Rigid Materials (Shore D): These are ideal for applications requiring greater structural rigidity and mechanical strength, like aerospace housings or defence electronics. They provide a robust, solid structure that can withstand significant mechanical loads.
Kohesi Bond’s Range
We offer a wide range of hardness options to meet diverse application needs. Our softer epoxy formulations are designed for electrical assemblies that require flexibility and vibration damping, especially under conditions of thermal expansion. In contrast, our rigid formulations provide structural reinforcement and robust sealing, ensuring greater system stability. By being able to precisely tune hardness across our various formulations, we provide engineers with greater design flexibility.
D] Coefficient of Thermal Expansion (CTE)
What is CTE and Why It Matters
The Coefficient of Thermal Expansion (CTE) measures how much a material expands or contracts in response to temperature changes, typically expressed in parts per million per degree Celsius (ppm/°C). For epoxy potting compounds, this property is critical. A CTE mismatch between the epoxy encapsulant and the underlying substrate, like a PCB or silicon die, can create immense internal stress during thermal cycling. This stress can lead to solder joint fatigue and interfacial cracking, causing premature device failure. This is especially relevant in aerospace, defence, and automotive equipment, which are subjected to wide temperature swings.
Tg and Fillers
An epoxy’s CTE is directly related to its glass transition temperature (Tg). Below the Tg, the material is in a rigid, glassy state with a relatively low expansion rate. However, once the temperature surpasses the Tg, the material softens, causing a significant increase in its expansion rate. By incorporating fillers like alumina or silica, it’s possible to reduce the compound’s overall expansion and flatten the CTE curve, mitigating dimensional mismatches. Standard epoxy CTE values typically range from 30 to 70 ppm/°C below Tg, but filled systems can be engineered as low as 20 ppm/°C to better match electronic substrates.
Kohesi Bond Solutions
At Kohesi Bond, we design potting compounds for electronics with lowered CTEs that can withstand extensive thermal cycling. Our formulations are engineered with the right combination of fillers to maintain maximum dimensional stability, protecting sensitive electronics in environments with extreme temperature variations. These solutions are deployed in mission-critical applications in defence and aerospace, where even minimal expansion can have catastrophic implications.
E] Beyond the Big Three: Additional Factors
While viscosity, hardness, and CTE are critical, other properties also play a vital role in a material’s suitability for an application. Ignoring these factors can lead to system failures, even if the “big three” are optimised.
Thermal Conductivity
In high-power electronic systems, heat generated by components can create localised hot spots, leading to premature failure. Thermal conductivity is a material’s ability to transfer heat away from these critical areas. For demanding applications, speciality grades of epoxy can provide thermal conductivity ranging from 0.2 W/m·K to over 1.5 W/m·K, effectively acting as a heat sink to protect sensitive electronics.
Dielectric Strength
Dielectric strength measures a material’s ability to withstand high voltage without electrical breakdown. Compounds with high dielectric strength (often above 15 kV/mm) are essential for applications with high-voltage components. This property helps prevent electrical arcing, suppress discharge, and maintain insulation, ensuring the system’s safety and performance.
Chemical and Moisture Resistance
For applications in harsh industrial environments, a material’s resistance to chemicals and moisture is paramount. Exposure to factors like humidity, hydraulic fluids, and corrosive agents can severely degrade an epoxy, compromising its protective barrier and leading to component failure. Choosing a material with strong chemical and moisture resistance ensures the electronic assembly can survive and operate reliably in these challenging conditions.
Our Multiproperty Engineering Approach
At Kohesi Bond, our engineering philosophy goes beyond optimising just a few properties. We take a multiproperty approach, designing epoxy compounds that balance and enhance all these factors to meet the rigorous demands of your specific application. This ensures a comprehensive, reliable solution that adheres to the strictest industry standards.
F] Why Choose Kohesi Bond for Epoxy Potting Compounds?
We aim to provide engineers with superior epoxy potting compounds that adapt to various operational requirements. Our commitment to quality, reliability, and service sets us apart.
1. Superior Formulations
Our epoxy formulations are engineered to perform optimally even in stress-heavy environments. We design our compounds to meet a wide range of operational needs, ensuring you get a solution that is perfectly suited for your application’s specific requirements.
2. Certified Quality and Consistency
All our manufacturing and quality systems adhere to both national and international standards. This ensures that every batch of our one-part and two-part epoxy adhesives is produced with the highest level of consistency and quality, providing you with a reliable and predictable product every time.
3. Reliable and Scalable Supply
We understand the importance of a stable supply chain. Our manufacturing flexibility allows for both low-volume prototyping and high-volume production, ensuring we can meet your demands as they scale. We are committed to maintaining enhanced delivery capacity to prevent any supply interruptions, no matter your market.
Ensure Maximum Reliability with Kohesi Bond Epoxy Potting Compounds
From precision viscosity control to tailored hardness and low CTE solutions, Kohesi Bond delivers engineered compounds that meet the strictest industry standards. Partner with us to protect your electronics in even the harshest conditions.
FAQs
You should select a compound based on your application’s specific needs. Consider key physical properties like viscosity for processing, hardness for protection, and the coefficient of thermal expansion (CTE) for thermal cycling. Additionally, you should factor in dielectric strength, moisture resistance, and chemical stability to match the compound to its operating environment and stress.
Viscosity determines how easily the epoxy flows. Low viscosity helps the compound penetrate fine gaps and fill dense PCB layouts, ensuring complete encapsulation. In contrast, high viscosity resists sagging and helps the compound hold its shape, making it suitable for applications that require dimensional stability. Choosing the right viscosity prevents air pockets and ensures a void-free finish.
The best hardness depends on the application. Use Shore A materials when flexibility and vibration damping are needed. Use Shore D systems when rigidity and mechanical strength are required. You should choose the hardness based on whether your assembly will face shock, flexing, or static loads.
Different materials expand and contract at varying rates when heated or cooled. A mismatch in CTE between the epoxy and the substrate creates internal stress, which could lead to solder fatigue, cracking, or delamination over time. Controlled CTE minimises these risks.
Yes. A lower CTE value is generally better for electronics because it reduces stress on components during thermal cycling. Sensitive components and fragile solder joints benefit from potting compounds engineered with low CTE fillers that closely match the expansion rate of the PCB.
Hardness defines how rigid or flexible the cured epoxy is. In real-world applications, a softer compound is ideal for absorbing vibration and protecting against shock, while a harder compound provides structural stability and robust protection against impact.
Low-viscosity epoxies are thin and flow easily, making them ideal for filling narrow gaps and complex electrical assemblies. High-viscosity epoxies are thick and more resistant to flow, helping them to retain shape and provide greater dimensional stability. They often contain fillers for added strength.
Our custom-formulated compounds are specifically tuned for your process and environment, ensuring optimal performance. We provide high-quality, consistent batches and reduce variability by adhering to certifications like ASTM E-595, USP Class VI biocompatibility, FDA standards, and UL flame retardancy. Our wide range of grades is field-proven in demanding industries like aerospace, medical, oil and gas, automotive, and electronics.
Utsav Shah is a 34-year-old entrepreneur with a passion for scientific discovery. Utsav’s journey began with a deep dive into materials science, earning degrees from USC and the Institute of Chemical Technology. He’s the visionary founder of Kohesi Bond, a top-rated adhesive manufacturer, and Cenerge Engineering Solutions, a leader in heat exchangers and cryogenic pumps. With over a decade of experience, Utsav consults across various industries, ensuring they have the perfect adhesive solution for their needs. Connect with him on LinkedIn!
