LED Processing with Lasers

LEDs are expected to develop into one of the predominant light sources over the coming decades. However, the pace of development differs, depending on specific requirements and constraints.

One promising market today is display backlight technology. Experts forecast quadrupling of the number of LCD displays with LED backlighting in 2010, superseding conventional cold-cathode fluorescent lamps. Laser marking is an essential step in manufacturing the required LEDs.

Dashboard lighting with LEDs. (Image: Rofin Sinar Laser)

To meet those criteria, Rofin Sinar Laser GmbH developed the PowerLine E 12 IC, a 532-nm laser with a double-head setup that offers high-speed marking with real-time compensation of position tolerances. Laser marking is demanding with 0.080-mm character height, 0.035-mm linewidth, exact positioning and more than 1000 characters per second. Engraving is done on a tiny area; for example, in white plastic housings.

Two ways to use LED backlighting in LCD flat panel TVs are: edge lighting and full array backlighting. The latter places ~100 backlight segments behind the screen, allowing for local dimming and a significant increase in contrast range. Each segment consists of hundreds of minuscule LEDs. Because each LCD display requires a huge number of LEDs, production must be fast and cost-effective.

Traceability marking of high-power LEDs

Mass market production of LEDs for LCD backlighting typically requires simple marking of type codes and connection labels. But there is also a growing market for high-power LEDs that require full product traceability, including the automotive and mobile phone industries. Interior lights of modern cars already make full use of LEDs. Stoplights, rear- and headlights will follow in the next few years, according to experts. Mobile devices rely on LEDs for display and keyboard backlighting, flashlights and more.

High-power LED production requires traceability markings on GaN, sapphire, SiC or GaAs wafers with OCR or T7 data matrix codes. Rofin says its Waferlase systems meet the requirements of wafer marking, ensuring traceability of the manufacturing process for fault analysis of semiconductor devices. The systems all produce marks that are machine readable,have no negative influence on subsequent manufacturing steps and permit clear identification at the end of the process chain.

PowerLine E 12 IC SHG lasers mark lead frames during the LED production process with minuscule 2-D matrix codes, made up of spots that are just 0.043 mm. Rofin’s PowerLine E 30 IC SHG lasers also mark white ceramics used as substrates for LEDs, with character heights of 0.15 mm and linewidths of 0.020 mm or ECC200 data matrix codes of 1-mm edge length.

Experts say LED backlighting technology will develop in several stages. Local dimming currently debuts in high-end displays and is expected to enter more price-sensitive segments, while red, green and blue (RGB) backlighting will find its way into the mass market.

For more information, visit: www.rofin.com