COB (Chip-on-Board) packaging technology is gaining more and more attention in the industry because of its low thermal resistance, high luminous flux density, small colour tolerance, and less assembly process, etc. COB packaging technology has been used in IC integrated circuits for many years, but the use of COB packaging for LED light sources is still a new technology for the majority of lamp manufacturers and consumers.
The reliability of LED products is closely related to the temperature of the light source, and the temperature distribution and measurement of COB light sources are significantly different from that of SMD light sources due to the high-density packaging of multiple chips.
COB package is to mount the chip directly to the substrate of the light source, when using COB light source and heat sink directly connected, without SMT surface assembly. SMD package is first mounted on the bracket to become a device when using the device needs to be mounted to the substrate and then connected to the heat sink.
Commonly used types of temperature sensors are thermocouples, RTDs, infrared emitters, etc. The thermocouple is composed of two different metal wire, one end combined together, the temperature change at the connection point will cause a voltage change between the other two ends, by measuring the voltage can be inverse of the temperature. RTD uses the mechanism that the resistance of a material changes with the temperature of the material, and calculates the temperature by indirectly measuring the resistance.
Thermocouple low cost, the most widespread in the field of temperature measurement, the smaller the size of the probe, the more sensitive to the temperature, IEC60598 requires thermocouple probe coated with highly reflective material to reduce the impact of light on the temperature measurement. However, if the thermocouple is directly attached to the light-emitting surface for measurement, the probe absorbs light and converts it into heat very obviously, which will lead to high measurement values.
The actual measurement of a number of technical personnel used to use high-temperature tape for the probe fixed, this bonding will exacerbate this light absorption into heat effect, resulting in the measurement value is seriously high, deviation of up to 50 ℃ or more.
Therefore, to avoid the influence of light on thermocouples, it is recommended to use infrared thermal imager for temperature measurement. In addition to the advantages of fast response time, non-contact, no power failure and fast scanning, an infrared thermal imager can also display the temperature distribution of the object to be measured in real-time. The principle of infrared temperature measurement is based on the Stefan-Boltzmann theorem.
In order to further study the thermal distribution of COB light source from the experiment, high reflectivity mirror aluminium is selected as the substrate as the object, this package structure, on the one hand, can significantly improve the light efficiency, on the other hand, the package form using the form of thermoelectric separation, no ordinary aluminium substrate insulation layer as a block, can further reduce the thermal resistance and junction temperature, to achieve high luminous flux density output of COB light source.
The above information is provided by COB light supplier.