Effective adhesive bonding and potting processes ensure the quality of LEDs and OLEDs
LED technology is increasingly replacing time-tested lighting sources such as halogen spotlights and fluorescent tubes. To achieve high quality lighting and long service life, LED modules are potted multiple times. This is usually done with vacuum processes, since it is the only way to ensure that the lens remains bubble-free and to effectively protect the LEDs against dirt and moisture.
Up to 90 percent more energy efficient than incandescent bulbs with a life of 50,000 hours, plus: LEDs (light emitting diodes) today are considered one of the most efficient and most promising lighting technologies on the market. When conventional light bulbs were facing their demise around 2008, other light sources such as halogen spotlights, energy-saving bulbs and fluorescent tubes were also increasingly being replaced by LED technology. They can be used in a wide variety of ways: First used mainly for signal lights and status indicators, LEDs are now used in automotive engineering, architecture, building and residential interiors and for public infrastructure lighting, such as street lights, traffic lights, LED backlit billboards and tunnel lighting.
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Potting processes provide long lasting, high quality lighting
Using a precise and high quality potting process is key to ensuring the long service life of LED components and continuously high quality lighting. This is particularly important when LEDs are used outdoors, since they are occasionally exposed to a wide variety of taxing conditions such as dirt, moisture, UV rays and temperature fluctuations. Even in the case of integrated lighting systems for indoor residential use, the potting quality and longevity are essential. For instance, materials that tend to yellow under the influence of light are not suited for optical LED potting. Moreover, it is important consider the properties required by the potting medium, such as those related to color, hardness, imperviousness, light transmission and temperature stability.
Cost-effective potting processes also play a key role in thermal management. Although LEDs are much more efficient than conventional light sources, they also produce heat. If this heat is not effectively dissipated, increased temperatures can have a negative impact on the life of the LEDs and in the worst case can even be the cause of faults and failures. Liquid thermal interface materials such as gap fillers or thermally conductive adhesives are used in order to implement an efficient thermal management system.
What many people don't know is that precise and repeatedly accurate dispensing and potting processes are essential even for the manufacture of OLEDs (organic light emitting diodes). Organic light emitting diodes consist of layers of organic thin films placed between two electrodes. These layers of films have to be hermetically sealed, since they would otherwise effectively become damaged by the effects of oxygen. For this purpose, special adhesives used with the right dispensing system are applied to the substrate and are then fit together.
LED potting: vacuum protects against dirt and moisture
To protect the LED diodes and related electronics from external influences, lighting manufacturers often previously resorted to using prefabricated plastic covers and enclosures. These are now increasingly being replaced by potting processes, and for good reason: Potted LEDs satisfy not only the tougher requirements for imperviousness and mechanical stability; with the right potting compounds, they may also occasionally have even better light properties, like light color and dispersion, than with the use of enclosures. Reduced storage costs as well as reduced handling and assembly costs are additional advantages.
Not only can air pockets in the material impact the light quality, but trapped contaminants and moisture can also damage the diodes. It is therefore important to always use the vacuum potting process for LEDs. In addition to purely functional criteria, aesthetic factors are also important: When dispensing processes are used instead of plastic enclosures, the potted resin is in the direct field of vision of the user or end customer. For this reason alone, a perfect, bubble-free appearance is required.
- The Scheugenpflug LiquiPrep LP804 provides reliable material preparation and feeding in a vacuum. The integrated temperature control also facilitates direct exertion of influence on the viscosity of the potting medium.
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- The proven vacuum potting systems from Scheugenpflug provide for effective and guaranteed bubble-free LED potting. Depending on the requirement, various cost-effective models are available that can be operated as standalone systems or can be integrated into the production line.
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TIP: For LED potting, the thermal expansion coefficients of the enclosure, LED substrate and potting compound must not differ too much from each other. If this is ignored, different thermally induced stresses can cause cracks and material separation, which not only destroy the mechanical bond, but also create leakage paths for moisture. Preliminary component and material tests can counteract this problem.