Knowledge LED Tutorial: LED Chips and LED Packages


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An LED chip is a bare semiconductor die that has a p-n junction sandwiched between oppositely doped layers. LED chips have a narrow spectral band and emit light of a single color. The selection of semiconductor and doping materials determines the spectral power distribution of light emitted from the LEDs. Green, blue, and ultraviolet (UV) LED chips are fabricated using indium gallium nitride (InGaN) chip technology. Red LED chips are currently based on aluminum indium gallium phosphide (AlInGaP) materials. There're no white LED chips as white light is a spectrum of different colors. White light is most often achieved with LEDs using phosphor conversion (PC) which involves down-converting all or part of photons emitted from blue or near-ultraviolet emitting InGaN LED chips to a lower energy level (longer wavelength).

Many people confuse LED chips with the term "LEDs". LEDs, unless otherwise indicated, refer to LED packages. An LED chip typically must be packaged before it can be used in a lighting application. The light source that constitutes a component for an LED luminaire or LED lamp is the LED package.

An LED package is an assembly of one or more LED chips which are arranged on a substrate, with an encapsulation formed on the chip, and thermal, mechanical, and electrical interfaces. Packaging plays multiple roles in that it protects LED chips from being damaged physically or chemically, provides electrical leads for connecting the semiconductor die to an external circuit, creates a thermal path to extract the waste heat away for the LED junction, and optimizes light extraction. The encapsulation may be mixed phosphors which down-convert electroluminescense from a blue LED or an ultraviolet LED to obtain a white light. An LED package may be designed as a single-chip a discrete light emitter or as an integrated array that includes multiple LED chips. The LED chip of the discrete light emitter is typically mounted on a carrier substrate made from sapphire, silicon carbide (SiC), silicon (Si), or GaN. An integrated LED array is typically mounted on the printed circuit board or ceramic substrate without using the carrier substrate.

There are a multitude of options regarding LED package platforms. Phosphor converted LEDs are primarily fabricated on these platforms: ceramic-based high-power packages, mid-power packages, chip-on-board (COB) packages, and chip scale packages (CSPs).