Chip-on-board technology (COB) is a method for the direct assembly of unpackaged semiconductor chips on printed circuit boards to an electronic assembly. The term COB is used for all assemblies that contain the naked semiconductor, whereas originally it was understood exclusively as assemblies with chip-and-wire technology. By eliminating individual packaging of semiconductors, the final product can be more compact, lighter and cheaper to produce. In COB technology is commonly seen where we find chips under black resin droplets on PCB. It is common for LCD modules like behind 1602A LCD module.
This technique is used for LED encapsulation by joining many LEDs in a semi-rigid resin. This type of LED package allows for achieving opening angles of up to 120°. In addition, being a single package, the heat dissipation of the LED is much greater, which improves its light intensity and durability. This type of encapsulation was initially used in spotlights since with a single LED a lot of illumination is achieved without the need for much power. Thanks to the evolution of LED products you can find bulbs that present this type of LED.
DIP LEDs are the LEDs we commonly use in DIY electronics and also they are used as indicator lamps. SMD LEDs are commonly used in various products which work as a source of light. COB LEDs offer certain advantages over conventional LED technologies such as SMD LEDs or DIP LEDs.
It is obvious that COB technology is allowing us a higher packing density of the LED array, this is what is referred to as efficient lumen density. Imagine a square area of 10mm x 10mm array. You can pack only 9 LEDs within that 10mm x 10mm array. In the case of SMD, you can pack 40 LEDs in the 10mm x 10mm array. In the case of COB, we can pack 342 LEDs in the same 10mm x 10mm array. The total chip will require just one circuit and two contacts. The less number and area of welding points result in a low rate of failure.
The resulting light will be of higher intensity and more uniformity. So this technology can reduce the footprint and energy consumption of the LED array.
However, there are disadvantages to COB LEDs. The first is the prohibitive cost. Secondly, the variety of colours is limited to cool white, neutral white, warm white, blue, green, red and pink. COB LEDs tend to run hotter and the diodes are pushed way harder out of the heat. Also, not always we need concentrated focussed light.
So, the usage of COB LEDs are mainly for producing decorative lights, flashlights, floodlights etc.