COB is short for Chip On Board, which means that the led chip is directly packaged on the PCB.
The COB light strip is a light strip that encapsulates the chip on a flexible board. Chips mostly use flip-chips, which are linearly solid-bonded on the PCB, and then a layer of packaging glue mixed with phosphor is directly dropped on the surface of the chip. The light emitted by the chip is refracted, reflected, and interacted with the phosphor inside the encapsulating gel. The gel uniformly emits light of different colors and color temperatures.

The COB led strips have a linear light-emitting surface due to their high chip density, while the SMD led strips can see obvious light spots and dark areas. Of course, this dark area and light spot can be solved by adding aluminum profiles and diffusers, just like this.
And COB light strips can become very uniform without adding diffuser. In this way, a lot of material costs and labor costs can be saved.