What is SMD？
SMD is the "surface mount device" led, which is the most used shared led in the market. LED chips are always integrated with printed circuit board (PCB), and are especially popular because of their versatility. PCB is built on a rectangular flat object, which is what we usually call SMD. If you look closely at the SMD LED, you will see a small black spot in the center of the SMD. That's the LED chip. You can find it in the light bulb and filament lamp, and even in the notification light on your mobile phone.
SMD LED chips have many sizes: 2835, 3030, 3014, 5050, 5630; they are called length and width according to their sizes. For example, 2835 is 2.8 x 3.5mm, 3030 is 3.0 x 3.0mm, 3014 is 3.5 x 2.8mm, 5050 is 5.0 x 5.0mm, 5630 is 5.6 x 3.0mm. The size of SMD chip is very small, which is close to the design of plane square computer chip.
Three diodes can be put on the same chip, so it has played an important role in the development of the LED industry. When the chip contains red, green and blue diodes, you can create any color you want by adjusting the output level of each diode on the chip. Because they are very bright and can change colors, they can be widely used in LED strips and bulbs.
What is COB?
A COB light is a type of LED light, with chips integrated on Chip-On-Board. COB lights are essentially an array of LED chips that are tightly packed together and bonded to a substrate such as silicon carbide. Like SMD, COP chips also have multiple diodes on the same surface. But the difference between COB and SMD LED lights is that COB LEDs have more diodes.
COB chips usually have 9 or more diodes. Regardless of the number of diodes, the COB chip has only one circuit and two contacts. This simple circuit design is the reason why COB LED lights have a panel-like appearance (on the other hand, SMD lights look like a group of smaller lights).
But unlike SMD, COB LED lights cannot be used to create color-changing bulbs or lights. This is because there are only 2 contacts and 1 circuit. Multiple adjustment channels are required to create a color changing effect. Therefore, COB LED lamps are highly efficient in monochromatic applications, but not efficient in more general technologies.
Advantages of SMD
（1) SMD is more flexible, the display of its chip is determined according to the layout of the printed circuit board, and it can be changed to adapt to different engineering solutions.
（2) The illumination angle of the SMD light source can reach up to 120 & Phi; 160 degrees. It is small in size, light in weightl, and high in assembly density. The size and weight of the cover part is only about 1/10 of the traditional plug-in part.
（3) High reliability and strong anti-vibration capacity.
（4) The solder joint defect rate is low, which improves the production efficiency.
Advantages of COB
（1) Better thermal conductivity.
（2) Smaller size
（3) Use less energy to produce more lumens.
（4) The circuit can be designed according to customer requirements, and the heat dissipation is more practical, which can effectively avoid the shortcomings of combining discrete light source devices and glare.