A COB LED is a surface-emission LED package that mounts an array of LED chips, known as “LED dies”, onto a metal-core printed circuit board (MCPCB) or a ceramic substrate to produce homogenous, high flux density illumination. It thus has this name because the chips directly attached to the circuit board rather than being enclosed in a plastic package as with mid-power LEDs. COB is abbreviated from "Chip on Board". The chip-on-board architecture reduces the package-level thermal resistance to a minimum, allowing a single LED package to accommodate multiple LED chips. A light emitting surface (LES) that is considerably larger than conventional packages makes COB LEDs the light source of choice to deliver clean, consistent and uniform lighting over a large area. With the ability to produce a well homogenized beam that behaves very much like a single large assembly of point sources, COB LEDs find their footprint in floodlights, high bay lights, street lights, and products that provide area lighting. Yet the largest application scenario of COB LEDs is directional lighting which is typically provided by spotlights and downlights.
In a COB LED, bare LED chips are die-bonded on the substrates with silver-filled epoxy and electrically interconnected using bonding wires which are often made of gold or copper. COB LEDs are similar to high-power single-chip LEDs when it comes to the design philosophy. However, thin bonding wires (15 - 50 µm) of COB LEDs make it challenging for COB LEDs to withstand high drive current operation in very high power applications. The chip array is covered with a phosphor silicone mixture while provide wavelength conversion while shielding the chips from the environment. Unlike the chip in a mid-power package is surrounded by a reflective cavity to improve light extraction, COB LEDs are constructed without sidewall reflection and are thus generally less efficacious than mid-power LEDs. On the other side, COB LEDs do not suffer from sidewall discoloration that not only leads to chromaticity shift, but also results in lumen depreciation.
In a COB LED, bare LED chips are die-bonded on the substrates with silver-filled epoxy and electrically interconnected using bonding wires which are often made of gold or copper. COB LEDs are similar to high-power single-chip LEDs when it comes to the design philosophy. However, thin bonding wires (15 - 50 µm) of COB LEDs make it challenging for COB LEDs to withstand high drive current operation in very high power applications. The chip array is covered with a phosphor silicone mixture while provide wavelength conversion while shielding the chips from the environment. Unlike the chip in a mid-power package is surrounded by a reflective cavity to improve light extraction, COB LEDs are constructed without sidewall reflection and are thus generally less efficacious than mid-power LEDs. On the other side, COB LEDs do not suffer from sidewall discoloration that not only leads to chromaticity shift, but also results in lumen depreciation.
