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Sealing of electrical pins and busbars as key technology for durable and robust drivetrain and power electronics components.
Electric auxiliary components such as oil pumps or compressors as well as new power electronics components place high requirements on sealing solutions. A central role is played by the sealing of electrical pins and busbars. This article describes the function of this application, the increasing requirements in the automotive environment, and shows how new sealant generations with improved material properties and modern curing concepts significantly increase efficiency and reliability.
New sealant generation
As the electrification of drivetrains progresses, the requirements for component sealing are noticeably increasing. Electric auxiliary units (such as oil and water pumps, compressors, control units) and new power electronics components (such as on-board chargers, inverters, converters) are crucial for electric vehicle operation. They take on central tasks in energy management and temperature control of electric vehicles. These components often operate under demanding conditions: in direct contact with motor oil or coolants and at permanently high temperatures as well as extreme temperature cycles.
OEMs and suppliers are therefore increasingly faced with the challenge of ensuring the reliability of their systems over long operating periods. Recurring leaks or the replacement of defective connectors cause significant follow-up costs. Accordingly, the need for more durable components grows, which can be realized through effective and specifically developed sealing adhesives.
Illustration of an oil pump where pin sealing is crucial for protecting the electronics from the oil environment; adhesive colored magenta for better illustration
A particularly critical area is the transition between electronics and mechanical assemblies. Pins and busbars often form the transition from the PCB to the outside of a unit, for example in electric oil pumps, e-compressors or power electronics. In pin sealing, electrical pins are protected. While in busbar sealing, flat conductors—which serve as conductors for energy transmission between components—are specifically protected against media and humidity.
They carry signals or currents out of the electronics and are exposed to special environmental influences due to their exposed position. This protection from external influences must be ensured even under extreme temperature stress. Even the smallest delaminations or cracks in the sealing cause media penetration, which in turn can lead to corrosion or even short circuits.
The requirements for sealing critical automotive components are constantly increasing. Over the years, not only have temperatures increased or test durations extended, but the speed and efficiency of the sealing curing process have also become a priority.
The basic principle of pin and busbar sealing:
To optimally meet these diverse requirements, new sealant generations based on polymers currently mark the greatest development step in this field. They combine significantly improved long-term media resistance with high bond strength and permanently consistent elasticity.
Their optimized flow properties enable precise wetting of complex geometries, while modern curing concepts allow fast, energy-efficient production processes. This combination of performance and process reliability makes the new material generation a central enabler for durable, robust and low-maintenance electric drive systems.
Illustration of pin (left) and busbar sealing (right); sealant colored magenta for better illustration
The material for sealing must withstand high thermal and chemical stresses. It is often in direct contact with oils, additives or coolants and is simultaneously exposed to temperature cycles between -40 °C and up to 160 °C.
Essential requirements for such high-performance polymers include:
These thermomechanical properties must remain consistently stable under temperature and media exposure, which is demonstrated through long-term storage tests. Specifically, this means that the sealant must exhibit minimal media swelling and low mass loss at elevated temperatures despite its wide-mesh, flexible network.
Currently, a new sealant generation marks a significant innovation step in this application field. The flagship product DELO DUALBOND GE4926 has proven itself as a new benchmark for sealing in first series applications and shows significantly improved properties compared to the previous generation. The swelling behavior after long-term storage in 160 °C ATF oil could be reduced by up to 85%. At the same time, adhesion after various oil and temperature storage tests show more than twice the durability on common substrates.
The elongation at break—an important mechanical characteristic for evaluating permanent elasticity—was also optimized: The decrease after long-term storage in various harsh media is about 20% lower, with simultaneously higher possible operating temperatures of up to 160 °C. These advances contribute significantly to raising the performance and reliability of heavily stressed components to new standards.
The spider diagram shows a significantly improved property profile of new developments like DELO DUALBOND GE4926 compared to previous generations—particularly under temperature influence
Sealing performance is determined not only by the material but equally by the geometry of pins and cavities. Undercuts, uneven gap widths or insufficient wetting surfaces can significantly impair sealing effectiveness. A coordinated interaction of material, dispensing strategy, flow behavior and curing process is crucial. These relationships apply analogously to busbar sealing, which places particularly high demands on wetting and curing behavior due to their flat and sometimes multi-layer conductor structures.
Optimized flow properties and appropriate processing time enable reliable introduction of the sealant into all areas of the cavity—even for complex components. Modern dispensing technologies and process monitoring, such as inline fluorescence control, ensure consistently high quality. Particularly for busbar, it is essential to control the flowing into the smallest gaps to cover the complete sealing area. This also applies to sealing in power electronics, where pins and busbars often have complex geometries with narrow gap widths and undercuts.
Various curing concepts are used depending on application and manufacturing requirements. Traditionally, heat curing processes are employed, especially for motor compartment requirements, as they ensure the highest reliability. Through new formulation possibilities, light-curing materials are now also available. These enable fast and energy-efficient processes. In many cases, eliminating ovens saves additional space and investment costs in manufacturing.
A widespread concept is dual curing, where the sealing compound is first fixed by light. It then cures completely in shadow zones through humidity. The assembly can be further processed and leak-tested immediately after light fixation. This shortens cycle times and enables gentle processing of temperature-sensitive components.
Schematic representation of a dual curing process: 1) Sealant dispensing, 2) instant light fixation with DELOLUX spot lamp 3) Final curing at room temperature (moisture curing in shadow zones)
An alternative method is Activation on the Flow. Here, light exposure occurs during dispensing. This begins the 5-10 minute open time during which the sealant has both good flowability and sufficient wetting ability to ensure sealing of the entire cavity even some time after preactivation. The sealant then cures to final strength without further steps.
Immediate further processing is possible if exposed sealant areas are additionally light-cured after joining, as this creates immediate initial strength and prevents sealant flow-out. Activation on the Flow thus combines short process times with high process reliability, is also suitable for complex geometries with undercuts, and conserves resources by eliminating energy-intensive oven steps.
Pin sealing via Activation on the Flow device DELO-ACTIVIS
The development of highly resistant sealing solutions remains a central task for the coming years. Current material solutions already offer very good resistance to common oils and coolants as well as stable mechanical performance at elevated temperatures. Nevertheless, new, aggressive media come to market annually, testing the resistance of sealant-based seals anew. These can be new, additive-containing motor oils or more cost-effective coolants.
The goal of ongoing development work is therefore to continuously test the best sealant solutions with new media and temperature requirements and to specifically optimize resistance in certain cases. The variance of automotive oils particularly requires continuous development of sealants. Depending on oil composition, diffusion and thus sealant swelling can change. Often, minor optimizations in the sealant formulation are sufficient to bring the described properties to the necessary level.
With these advances, pin and busbar sealing technology will further solidify its role as a central component of modern electrified drive systems and associated power electronics—regardless of whether battery- or fuel cell-based concepts determine the drive.
Request the technical data sheet for DELO DUALBOND GE4926 now and learn how the new sealant generation advances your e-mobility projects.
Technical presentation: “New high-tech light curing adhesives for e-motors: Pin- and busbar sealing as key technology for robust protection of electronics” [03:20 p.m./Hall 2]
Booth 5-B15: Live demonstrations and expert consultation
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