A Little Drop of Silicone - Wacker Chemie AG

A Little Drop of Silicone

… but a big step for efficient mass production of LEDs. High-performance LUMISIL silicones from WACKER now allow LED manufacturers to create optical lenses by placing a drop of silicone directly onto the chip—and eliminating complex injection-molding steps in the process.

Cross-section through an LED with silicone lens

The LED Success Story

In the three decades following their invention in 1962, light-emitting diodes were only a niche market. Emitting only colored light (primarily red, yellow and green), LEDs were used in applications such as automobile dashboard displays or standby indicators in electronic equipment. The infrared version was used in IR transmitters for remote controls.

It was not until blue and white models came onto the market in the 1990s that applications for LEDs began to expand steadily. According to the market research agency DisplaySearch, every fourth LCD television sold throughout the world in 2010 was made with LED backlighting, and LED running lights have made the transition from the luxury class to mid-sized and compact cars.

The market for general lighting (street, storefront and ambient lighting), long neglected by LED manufacturers, has been experiencing rapid growth for roughly two years now. OSRAM, one of the world’s leading lighting manufacturers, expects the market volume for LEDs to nearly triple by 2012. Growth in the general lighting market can also be attributed to bans on classic incandescent bulbs, which, due to their poor energy efficiency, are being phased out in most industrialized nations.

Longer Life, but Complicated Production Process

LEDs not only represent an improvement over incandescent bulbs, however – in many respects they are also superior to what is currently the most common alternative, i.e. the compact fluorescent tubes, popularly known as energy-saving bulbs. With an average life of 50,000 hours, LEDs last considerably longer than energy-saving bulbs (roughly 10,000 hours, depending on the model), they have a higher light output (which will eventually reach some 200 lumens per watt in top models), they do not require toxic mercury and their light appears warmer and more natural in color than the colder light of fluorescent tubes. Fluorescents, however, are less expensive and distribute light more evenly throughout a room.

The high purchase price is currently all that stands in the way of the widespread adoption of the LED. In addition to the diode itself, however, there is another factor that drives up manufacturing costs: the silicone lens, which radiates the light and, at the same time, protects the semiconductor component from the environment. Until now, LED manufacturers made these lenses in a complex injection molding process requiring not only expensive injection molding equipment, but also high-precision molds as well as sorting, dispensing and assembly equipment – a total of five steps, which, to make matters worse, also had to be performed under cleanroom conditions.