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|Thermal Modeling and Experimental Analysis of High Power LED using POL-kW Packaging Technology|
|Keywords: Advanced Packaging, LED, Thermal analysis|
|Introduction: The reduction in form factor and increase in the power rating and density of LED modules has led to an increase in new developments in packaging and strategies adopted by the users. With the advent of the bare die or CSP LED, manufacturers have been moving to flip chip attach methods for these components. Since the light is emitted from the top of the flip-chip die, as compared to other power devices, the flip-chip die has only one thermal dissipation path at the bottom of the die. Therefore, when using a flip-chip structure, the removal of heat is a challenge, and is typically done by mounting the LED die to an AlN based substrate. Power Overlay Kilowatt (POL-kW) packaging technology is used for packaging High Power Wide Bandgap devices and has demonstrated thermal benefits in these applications. In this paper, we will look at the use of the POL-kW technology for High Power LED applications. The authors will describe thermal modeling analysis as well as experimental results. In this paper, an “embedded chip” packaging platform using POL-kW packaging for High Power LED devices is presented. Description of POL-kW and Technical content: Power Overlay Kilowatt is an advanced embedded packaging platform for power electronics developed by GE over the past decade, and now in production at several partner locations. The platform enables higher efficiency and power density, with reduced parasitics, which greatly improves the performance of the Power Modules. This packaging platform is intended for applications of motor drives and power conversion in automotive, aerospace, and renewable industries. In such applications, superior reliability and stable long term performance in harsh environments are some of the key requirements. These characteristics are also desirable for High Power LED applications. POL-KW uses a polyimide-based substrate and a direct metal interconnect method. An adhesive layer is used to attach the dies to the polyimide film. Vias are formed by laser drilling, followed by sputtering and electroplating to form an electrical and thermal connection to the semiconductor dies and the interconnect routings on the polyimide surface. The via interconnects offer significantly reduced parasitic inductance and resistance, while providing a thin profile and a direct copper electrical and thermal connection to the die. The diagram below shows a typical POL-kW process flow. In this paper, we will evaluate GE’s POL-KW packaging technology for High Power LED modules. A thermal simulation model has been developed to look at the POL-kW structure and will be compared to an AlN based LED package. Thermal properties and attributes will be discussed. Process flow and fabrication details will be summarized of a POL-kW LED package, to provide a better understanding of the technical and performance advantages. These demo POL-kW LED modules will then be tested to verify electrical and thermal properties. Surface temperature of the prototype LED module will be measured using infrared (IR) imaging analysis. These experimental results will be compared to the simulation model to validate the results. This model will then be used to validate other designs and configurations in regards to thermal performance, in both steady- and transient states. Summary: High power LED modules are becoming more common and are implemented in areas such as automotive and specialty lighting. These High Power LEDs also pose a thermal packaging challenge; and packaging engineers are looking at new ways to package and implement these High Power LED dies. The traditional LED module packaging methods still limit their full potential at the module and system levels. Early findings show that GE’s POL-kW packaging technology can offer an alternative thermal solution to AlN based packages, while at the same time, provide a thinner and potentially cheaper solution. Data presented in this paper will show the progression of thermal modeling comparisons, to packaging of prototype devices and the experimental results of IR imaging. The POL-kW packaging platform was demonstrated as a possible alternative to AlN based LED module packaging.|
|Christopher Kapusta, Senior Process Engineer
GE Global Research Center