Silicone Rubbers For Potting Light-emitting Diodes

The new LED casting compounds Lumisil 740 and Lumisil 770 are formulated in two components. They crosslink at room temperature through a platinum-catalyzed addition reaction. After vulcanization, they have a refractive index of 1.41, which is typical for polydimethylsiloxanes. The two products therefore belong to the group of casting compounds with a normal refractive index, also known as “normal refractive index encapsulants”. The casting compounds effectively protect the sensitive semiconductor chip of the light-emitting diode from environmental influences. They can also be used as substrates for luminescent dyes. With such dyes, the color of the light emitted by the light-emitting diode can be influenced in a targeted manner.

A special feature of Lumisil 740 and Lumisil 770 is, according to the manufacturer, their enormously high resistance to heat, light and temperature changes. After storage for 500 hours at 245 degrees Celsius, neither yellowing nor embrittlement should be visible on test specimens made from Lumisil 740. Lumisil 740 proves to be particularly resistant to combined heat and light exposure. In the temperature change test between 125 and –45 degrees Celsius, both materials survive more than 1000 load cycles. The potting compounds can therefore also compensate for thermomechanical stresses that arise in the light-emitting diode as a result of the different thermal expansion of the materials used.

The viscosity of the two encapsulation materials is adjusted so that they can be applied easily by dispensing. Lumisil 740 and Lumisil 770 are formulated to be self-adhesive. They adhere to the semiconductor chip and to the usual reflector and housing substrates without having to be pretreated. (qui)

K 2016: Hall 6, Stand A10