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Shock-resistant New Silicone Rubber from WACKER for LED Encapsulants at K 2016

Published on 2016-10-05. Author : SpecialChem

MUNICH -- WACKER will unveil two new encapsulation compounds for light-emitting diodes (LED) at the 20th International Trade Fair for Plastics and Rubber K 2016 in Düsseldorf, Germany.

  • The encapsulants LUMISIL® 740 and LUMISIL® 770 cure to form highly transparent silicone elastomers. 
  • Both silicones withstand exceptionally high operating temperatures and strong light radiation without yellowing or becoming brittle. 
  • They are ideal for encapsulating high-performance LEDs. 

Silicone LED Encapsulant
Silicone LED Encapsulant

K 2016 will take place from October 19 to 26, 2016.

Silicone for LED Encapsulants

  • The new LED encapsulants LUMISIL® 740 and LUMISIL® 770 are two-component systems with high transparency
  • They cure at room temperature via a platinum-catalyzed addition reaction. 
  • The cured rubber grades have a refractive index of 1.41, which is typical of polydimethylsiloxanes. 
  • The two products thus belong to the group of normal refractive index (NRI) encapsulants. 
  • They effectively protect the sensitive LED semiconductor chip against environmental influences. 
  • They can additionally serve as carriers for luminescent dyes, which can selectively influence the color of the light emitted by the LED.

Uniqueness of LUMISIL® 740 & LUMISIL® 770

A special feature of LUMISIL® 740 and LUMISIL® 770 is their extremely high heat, light and thermal-shock resistance. Corresponding aging tests confirm this. After 500 hours of storage at 245 degrees
Celsius, LUMISIL® 740 test specimens display neither yellowing nor embrittlement. Even after 1,000 hours, the change in the cured rubber grades is insignificant. LUMISIL® 740 has proven particularly resistant to combined heat and light exposure. In a thermal shock test going from +125 to -45 degrees Celsius, both materials withstand more than 1,000 test cycles. The encapsulation compounds are thus able to compensate thermo-mechanical stresses that can arise as a result of the different thermal expansions of the LED materials.

WACKER at K 2016

Difference Between LUMISIL® 740 & LUMISIL® 770

Due to their stability, the new silicones are particularly suitable for encapsulating LED chips with strong heat generation and intense light emission.
  • The two grades differ mainly in the hardness of the cured products. 
  • LUMISIL® 740 cures to form a material with a Shore A hardness of 50, while LUMISIL® 770 is formulated to be slightly harder at Shore A 70. 
  • LUMISIL® 740’s property profile makes it ideal for the encapsulation of multi-chip LEDs that are applied using the chip-on-board technology – mounted directly onto the printed circuit board, tightly packed, without casing. On the other hand LUMISIL® 770 is the material of choice for encapsulating single-chip LEDs.

The viscosity of the two encapsulation materials has been adjusted so that they can easily be applied by dispensing. LUMISIL® 740 and LUMISIL® 770 are self-adhesive. They adhere to the semiconductor chip and to conventional reflector and casing substrates without pretreatment.


WACKER is a globally-active chemical company with some 17,000 employees and annual sales of around €5.3 billion (2015). WACKER has a global network of 25 production sites, 22 technical competence centers and 50 sales offices.

WACKER Silicones
Silicone fluids, emulsions, rubber and resins; silanes; pyrogenic silicas; thermoplastic silicone elastomers.

WACKER Polymers
Polyvinyl acetates and vinyl acetate copolymers in the form of dispersible polymer powders, dispersions, solid resins and solutions.

WACKER Biosolutions
Biotech products such as cyclodextrins, cysteine and biologics, as well as fine chemicals and PVAc solid resins.

WACKER Polysilicon
Polysilicon for the semiconductor and photovoltaic industries.

Hyperpure silicon wafers and monocrystals for semiconductor components.

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Source: WACKER
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