What is COB? Fully flip-chip vs. fully flip-chip COB advantages?

A CoB LED, or chip-on-board LED, is a single device with many LED chips mounted on a thermally efficient substrate that sits beneath a uniform phosphor coating.

Anyone who has walked through a store or home with recessed or track lighting has likely experienced the light from a chip-on-board LED (CoB). CoBs are widely used because they emit bright white light output from a compact source and are highly efficient in a wide range of applications. So what is a CoB LED and how does it differ from other types of LEDs?

CoB (chip-on-board) refers to the way the LED unit is constructed. The basic elements 

The power supply that provides the energy to drive the LED, the light-emitting chip or "die". This is sometimes called a blue pump and is made of the semiconductor material Indium Gallium Nitride (InGaN), which emits blue photons when powered

The phosphor coating, which converts blue light to white light. The chemical composition of the phosphor is controlled to produce light of a specific color temperature

A cross-section of a COB LED shows multiple connected LED chips sitting on a circuit board beneath a uniform phosphor coating.

CoB LEDs: Space-Saving Arrays of Multiple LED Chip

A CoB LED is a single device with many LED chips mounted on a thermally efficient substrate or circuit board. Each chip is a bare die - that is, the chip does not have its own lead frame, phosphor coating or lens. This means that the chips can be mounted very closely on the substrate. The close placement of the LED chips allows high intensity or light density to be emitted from a smaller area than a single packaged LED. CoB LED manufacturers then apply a uniform phosphor coating to the entire array of chips to convert the blue light to the desired white temperature.

Advantages of CoB LEDs

A single CoB LED can contain hundreds of chips, forming a dense array. This dense array enables CoB LEDs to produce more light output from a smaller area than is typically possible with an array of packaged LEDs.

Using a single LED simplifies the design and product and provides optical advantages for uniform light and efficient optics.

Electrical design is simpler because CoB LEDs only require a single two-wire power supply to power the entire array of chips. The positive and negative terminals on the CoB LED are clearly visible in the LUXEON CoB Core Range product image above. In contrast, packaged LED arrays require dedicated power traces to be routed on the PCB to each LED unit.

Production is simpler because there are fewer units to solder to the board if CoB LEDs are used instead of packaged LED arrays.

From an optical perspective, various optics (usually reflectors) can be used with different sized CoBs to determine the direction and width of the beam, such as a spotlight or floodlight.

Finally, the color of CoB LEDs can be more consistent because the entire chip array is coated with a phosphor coating, while in a packaged LED array, each LED unit has its own phosphor coating.