When designing COB light source luminaires, luminaire manufacturers often use thermocouples to measure the temperature of the light-emitting surface of the light source. This measurement method will make the measurement result significantly higher, and then have doubts about the reliability of the COB light source.
The temperature of the light-emitting surface of the COB light source is relatively high. On the one hand, the light source has a high luminous flux density output, and the fluorescent glue absorbs light into heat; on the other hand, the temperature of the light-emitting surface is not suitable for contact measurement by a thermocouple.
I. Introduction
COB (Chip-on-Board) packaging technology has attracted more and more attention in the industry due to its low thermal resistance, high luminous flux density, small color tolerance and few assembly processes. COB packaging technology has been used in IC integrated circuits for many years, but for the majority of luminaire manufacturers and consumers, LED light source is COB package or novel technology.
The reliability of LED products is closely related to the temperature of the light source. Since the COB light source is packaged in a high-density chip, the temperature distribution and measurement are significantly different from those of the SMD light source. This paper will introduce the temperature distribution characteristics of COB light source and its internal mechanism, and compare the commonly used temperature measurement methods.
Second, the temperature distribution of the COB light source
The COB package is to directly mount the chip on the substrate of the light source. When used, the COB light source is directly connected to the heat sink, and no SMT surface assembly is required. In the SMD package, the chip is first mounted on the holder as a device, and the device needs to be mounted on the substrate and then connected to the heat sink. The schematic diagram of the thermal resistance structure of the two is shown in Fig. 1. Compared with the SMD device, the COB thermal resistance is less than the thermal resistance of the stent layer and the thermal resistance of the solder layer when the SMD is used, and the heat of the chip is more easily transmitted to the heat sink.
Figure 1: Schematic diagram of thermal resistance structure
1, comparison of common temperature measurement methods
Commonly used temperature sensor types are thermocouples, thermal resistors, infrared radiators, and the like. A thermocouple consists of two different wires that are joined together at one end. The temperature change at the junction causes a voltage change between the other ends. The voltage can be reversed by measuring the voltage. The thermal resistance calculates the temperature by indirectly measuring the resistance by using the mechanism of the resistance of the material as a function of the temperature of the material.
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