Abstract: The luminescence properties of LEDs are not only related to their electrical properties, but also affected by their junction temperature. Therefore, it is very important to study the heat dissipation performance and thermal management methods through actual test and simulation tools in the LED design process. In this paper, the electrical, thermal and optical properties of LEDs are studied collaboratively. In terms of simulation, the electro-thermal simulation of a board-level system was completed; in terms of testing, the application of a thermo-optical joint test system was discussed.
It is well known that the effective optical radiation (luminosity and/or radiant flux) of an LED is severely affected by its junction temperature (see Figure 1). A single LED package is often referred to as a primary LED, and an LED assembly with multiple LED chips mounted on the same metal substrate is commonly referred to as a secondary LED. When the secondary LED requires high light uniformity, the problem that the junction temperature will affect the LED luminous efficiency will be prominent. Of course, the electrical, thermal, and optical synergistic models of the primary LED can be used to predict the electrical, thermal, and optical properties of the secondary LED, but only if the LED's thermal environment needs to be accurately modeled.
Figure 1: The relationship between the effective light radiation of a group of LEDs from green to blue and white light with junction temperature
Note: Data from the performance data sheet for the Lumileds Luxeon DS25
In this article, we will discuss how to use the structure function to obtain the thermal model of the LED package, and briefly describe a new test system that we use to test. In addition, we will review the principles of the electro-thermal simulation tool and then extend this principle to board-level thermal simulation to help optimize the simplified thermal model of the package structure. At the end of the article, we will introduce an application example.
Establish a simplified thermal model of the LED package
The academic community has been discussing the establishment of a simplified thermal model (CTM) for semiconductor package components for more than 10 years. Now, for the establishment of packaged components, especially IC packages, independent of the boundary conditions of the steady-state simplified thermal model, the DELPHI approximation processing method is generally accepted. In order to study the transient thermal performance of components, we need to extend the CTM. The extended model is called Transient Simplified Thermal Model (DCTM). The EU has developed a method for building component DCTMs through the PROFIT project and has also expanded the capabilities of thermal simulation tools to enable simulation calculations of DCTM models.
When the CTM application is under specific boundary conditions or the package component itself has only one junction-environment heat flow path, the NID (thermal resistance network customization) method can be used to model the component.
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