Feature: Enclosures
Companies that supply military
assemblies, such as lighting for warships, should consider Mil-SPEC testing of characteristics relating to operational durability, ruggedness and reliability. And, if the potting compound is designated for a medical device, the designer must consider the ISO 10993 specification.
Choosing the material Aſter establishing the environmental protection level required and determining the industry’s testing regime, the design engineer can begin to narrow down the choices to an appropriate chemistry. Tis involves many factors, like desired harness, resistance to yellowing, clarity, thermal conductivity, cost and processing methods. For products where the LEDs are seen,
Figure 1: Pisces Deep selective fishing light in its enclosure
Choosing an LED potting compound and
enclosure By Kevin Brownsill, Head of Technical, Learning and Development, Intertronics
P
otting and encapsulation are commonly used to protect LED assemblies from shock, vibration, the environment and their thermal management.
Tere are many compounds available, with formulations offering properties like low density and low weight, flame retardant, flexible, optically clear and thermally conductive, which can make it challenging to choose the right one. LEDs are found everywhere, used
for both indoor and outdoor lighting. Whatever the application, LEDs assemblies and modules need protecting
34 May 2024
www.electronicsworld.co.uk
from dust, debris, moisture, pressure, impact, vibration and chemicals. For this there are two main options: seal them into an enclosure with a lens, or pot them with resin. LEDs generate heat as well as light, so
there are oſten additional requirements for their thermal management. Potting the non-optical side of the assembly with a thermally-conductive potting compound helps here. Te level of protection required from potting depends on the product’s final environment. For example, swimming pool underwater lights must be fully waterproof, to IP68, and be resistant to chlorine and other chemicals.
an optically clear coating is normally used on the front of the product, but not necessarily on its rear, where a different material will offer the desired thermal management characteristics. For LED assemblies that require clear
finish, there are three main chemistries: polyurethanes (PUs), epoxies and silicones – each with its own advantages and disadvantages.
Polyurethane potting compounds We typically recommend that customers test polyurethane materials first, due to their versatility, hardness, reasonable price and UV resistance. Tese two-part materials cure at room temperature, and their 1:1 mix ratio means they are easy to handle and use. PUs are available in various packages, from small to large two-part cartridges, twin-packs and bulk containers. Tey have good long-term UV resistance and can be formulated with anti-UV additives that prevent yellowing, making them popular for outdoor use. Many customers start with the Opti-tec 4200, a clear polyurethane resin. Available in double syringe or twin-pack sachets, the material is easy to mix and apply and cures to a clear, scratch-resistant finish. It is also available as Opti-tec 4220, a semi-opaque, milky-white version with an aesthetically pleasing finish, yet allowing high light transmission whilst hiding the underlying electronics.
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