Complete thin film material offering and refining services
LEDs (Light Emitting Diodes) and High Brightness (HB LED's) have experienced tremendous growth during the last two decades. The market for LEDs is expected to grow to nearly $7 billion in 2009. Incredible amounts of research and development have yielded numerous applications for LEDs including: traffic control lights, instrumentation illumination, digital displays, indicator lights, some fiber optic applications, cell phone applications and, in the future, the general lighting market.
Williams Products Used
Williams products are intrinsically involved in the production of LEDs. Gold sputtering targets featuring SFG™ technology and gold evaporation materials featuring EVAPro™ technology are used for metallization of the wafers at the contact surface. Platinum and palladium sputtering targets are also occasionally used for the same application. Williams AuSn and AuGe sputtering targets featuring VCT™ technology are also used in the manufacturing of LEDs, but are used for attachment metallization. Traditional AuSn and AuGe preforms can also be used for this application.
Williams also offers a full array of backing plate designs and internal services including the ability to replace, refurbish, repair and design backing plates using CAD/CAM. With target bonding facilities throughout the world, Williams assures industry leading bonding services and minimized shipping logistics.
What are LEDs?
A LED is essentially a p-n junction that is operated with a positive bias (opposite that of a photodiode). As the positive bias is applied to the LED, the current begins to flow from the n-type semiconductor into the p-type semiconductor. At the p-n junction the electrons combine with the holes, therefore releasing energy in the form of light. This current flow can be seen schematically in the following figure:
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Figure 1: Schematic diagram showing the current flow in a LED
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The color of light emitted by an LED depends on the size of the band gap in the doped semiconductors. The wider the LED bandgap, the shorter the emitted wavelength, for instance, LEDs that emit red light have a smaller band gap than LEDs that emit yellow light.
The basic LED structure consists of the die or light-emitting semiconductor material that is attached to the base of the reflector with an electrically conductive epoxy. Gold wire is used to connect the metal contact on the top of the LED die to the adjacent pin. A ball bond is formed on top of the LED die and a wedge bond is used to attach the wire to the adjacent pin. Finally, the epoxy package is molded around the leadframe using either a casting or transfer molding process.
Schematic Diagram
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Figure 2: Enlarged schematic of a typical T-13/4 LED
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Figure 3: Expanded view of a blue InGaN semiconductor
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