Multi-Domain Characterization of Cob Leds

Abstract

In a recent European H2020 project on LED characterisation and modelling (Delphi4LED, www.delphi4LED.eu) the major target was to represent physical LED package types by their digital twins in form of multi-domain compact models. In this project a specific task was devoted to CoB LEDs. Phosphor converted white CoB LEDs are large area devices on a ceramic substrate of high thermal conductivity, with a few dozens of LED chips mounted, covered by a phosphor layer. Such devices represent real technical challenges both in terms of their physical measurement and modelling. In this paper we report on our work regarding measurement and modelling of such devices performed in the context of the aforementioned project.

Mixed Detailed and Compact Multi-Domain Modeling to Describe CoB LEDs

“…Though Bachmann in his PhD dissertation [42] provides detailed measurement data of different kinds of phosphors, including a few graphs showing the temperature dependence of luminescence intensity, there is no data on efficiency and thermal properties of phosphor powder-resin composites; the limited data on the temperature dependence of luminescence intensity could not be used for our modeling purposes. As a workaround to the problem of lack of sufficient data on temperature-dependent behavior of phosphors, we had the following approach [25]:…”

“…) On the one hand, these LEDs with known properties have been used for extracting material properties for the multi-domain model as mentioned above [25], and on the other hand, for validating the overall simulation approach (with the blue chip multi-domain compact model embedded), simulating them characterized single-chip white LEDs well. The major steps of extracting the phosphor layer parameters were the following: On the one hand, these LEDs with known properties have been used for extracting material properties for the multi-domain model as mentioned above [25], and on the other hand, for validating the overall simulation approach (with the blue chip multi-domain compact model embedded), simulating them characterized single-chip white LEDs well. The major steps of extracting the phosphor layer parameters were the following: (a) Spectral power distributions for all manufactured custom-made white LEDs have been measured (along with the spectra of the used bare blue LEDs before attaching the phosphor + lens structure).…”

“…We measured and modeled a Lumileds 1202s CoB LED device which consists of 24 LED chips (two strings of 12 LEDs, connected in parallel) with a lateral dimension of 600 µm × 700 µm each, placed on an aluminium pad with solder layer between them, covered by a phosphor layer, see Figure 23a. The parameters of its phosphor coating were measured as outlined in Section 3.2, see further details in Reference [25]. A 3D model was created for simulation ( Figure 23b).…”

“…This paper, as a significantly extended version of our THERMINIC 2019 conference paper [23] provides a comprehensive summary of our CoB LED multi-domain modeling related work (parts of which have already been published at other conferences as well [24,25]) completed with a few, recent measurement results. Figure 1.…”

“…The α blue and α yellow attenuation factors are temperature-dependent material parameters of the cell. The η conv and η yellow_re blocks represent the blue-to-yellow and yellow-to-yellow conversion efficiencies, which are temperature-dependent material parameters, as seen in Equations (25) and (26).…”