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Understanding LED components - LED Chips
What are the components that make this LED spotlight work?
Most of us are familiar with LED lights as the new energy-efficient alternative lighting source that can save you money. But what exactly are the components that make up the LED light? In a multiple part series we will look at each component in detail!
The foundation - LED Chips
The most fundamental and crucial component is the LED chip, also known as the die. The LED chip is where all the action happens - it is the diode itself (as in Light Emitting Diode), and is oftentimes the most cost-intensive component in LED product manufacturing.
A close-up photo of a single 45x45 mil LED chip
A diagram of an F5 type lamp showing where the LED chip (semiconductor die) is located.
They are made of a semiconductor material and are thin and rectangular in shape. The chips are very small- standard measurements are 10x16, 10x23, or 45x45 mils (thousandths of an inch) - to see a single chip clearly, a microscope is needed.
One of the reasons why LED chips comprise a significant portion of the total cost in producing an LED product is due to its extremely high-precision manufacturing process. LED chips are manufactured through MOCVD (Metal-organic Chemical Vapor Deposition), which is a process of growing layers of semiconductor crystals by allowing semiconductor particles to crystallize from gas phase.
LED chips are typically sent to LED manufacturing facilities on plastic, static-proof sheets.
How are they handled?
When shipped, these LED chips come on a static-proof sheet in an array (see picture above). This plastic sheet is then stretched onto a circular plate, and fed into a dedicated machine with a high-precision arm which transfers each chip from the sheet onto each LED package housing, where it is secured via an insulative glue. LED chips have a negative and positive terminal, to which gold wires of about 1.0-1.2 mil are welded on to. Gold wires are preferred due to their malleability.
Dedicated LED chip mounting machines take the LED chips from the film and
mount them onto the LED package housing using an insulative glue.
High precision welding machines attach the gold wires to the terminals
After the wires are welded on
What are the properties of the chip?
are the fundamental component in LED products, LED chips are the dominant
factor in determining light quality. The chips have various ratings for
brightness, emitting wavelength, and voltage. When an LED chip is connected to
an electrical source and a current runs through the chip, light of a certain
color is emitted. Most chips used in LED manufacturing are InGaN
chips that emit a blue colored light with a wavelength of 450-460 nanometers,
using about 3 volts.
Blue light at around 450-460nm is typically emitted by the InGaN LED chips. What we perceive as white light is a mixture of all colors in the electromagnetic spectrum.
Of course, for most practical lighting applications, a light source that produces only blue light is problematic. Recall that white light, as we perceive it, is an amalgam of all colors of the spectrum. As of now, however, there are no commercially viable ways for an LED chip to directly produce white light. Therefore, the most cost effective way to create white light is to use LED phosphors, chemical powders which convert blue light into other wavelengths, turning the blue light into what we perceive as white light through what is called PC (phosphor conversion) or Stokes shift. This is known as phosphor down-conversion because we are converting higher energy blue light to lower energy wavelengths.
Brightness, of course, is of high importance because the brightness of the chip is what determines the brightness and electrical efficiency of the final LED product. Additionally, voltage is typically indicated as a range rather than a precise number, which is one of the causes of variation in the final product's light output. These variations are inevitable due to the nature of the LED chip manufacturing, and consistency and quality issues are addressed later on through the binning process.
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