Difference of COB and SMD packaging

Currently, LED floodlights use COB and SMD packaged by mainstream led light source.

COB PackagingSMD Packaging

COB package: Because of the multi-chip packaging, the luminous region can accommodate several times the standard LED light source, thus greatly increasing the lumen output per square inch. Another reason COB can reduce the failure rate is that a single LED chip no longer needs spot welding, because each chip is directly mounted on the substrate. Less solder joints mean lower failure rates.

The difference between COB and SMD lies in heat dissipation, luminous efficiency and dazzle.

Heat dissipation

The size of 9W COB is a circle with a diameter of about 10mm, which determines that it can only act directly on the heat source in this area, and the range outside the area is only used as an auxiliary heat dissipation. For the same 9W SMD, the diameter of the substrate is generally about 100 mm.

For heat dissipation, the situation of low calorific value and large area heat dissipation is much better than that of high calorific value and small area heat dissipation.

Luminous efficiency

The second disadvantage of COB is luminous efficiency. Many LED chips are arranged tightly in a narrow area, so the light emitted by a single chip near the horizontal direction will encounter adjacent chips and continuously form a total reflection, which will be absorbed by packaging materials and can not be emitted.

For SMD, as long as the spacing is reasonable, there is no such problem. It is this total reflection that makes the luminescence efficiency of COB 10% lower than that of SMD from the beginning. At the same time, the heat generated by the packaging material absorbing horizontal light and the heat generated by the chip's dense arrangement itself are superimposed, which leads to the higher COB working temperature and affects the light efficiency of the chip again.

COB light source products generally have high power and high surface temperature of packaging glue. Considering the thermal resistance of packaging glue, the glue with refractive index n=1.41 will be used. However, the glue with refractive index n=1.5 will be used for single device with low power and low surface temperature. The higher the refractive index is, the better the LED chip (n = 2) will be. At the same time, because of the high refractive index of the glue, the thermal resistance of the glue is poor (the molecular structure of the glue causes the characteristics).

Dazzle

Similarly, because of the small area and high power of COB, there is inevitably a glare problem. Basically, the spotlight using COB must be equipped with a very deep lamp cup, in addition to the need for light distribution, it is also to prevent too strong glare. (Definition of Dazzle: refers to the visual condition that causes visual discomfort and reduces the visibility of objects due to inappropriate brightness distribution or extreme brightness contrast in space or time in the field of vision. The visual field produces a light sensation that the human eye cannot adapt to, which may cause disgust, discomfort and even loss of vision. In the field of vision, there are excessive brightness or excessive brightness changes in a part of the area.)

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