LAMINA THERMAL MANAGEMENT User Manual

Bright Lights. Bright Ideas.

APPLICATION NOTE 02

THERMAL MANAGEMENT OF LAMINA HIGH B

RIGHTNESS LIGHT ENGINES

LAMINA SUPER-BRIGHT LED A

RRAYS

AS THE MARKET LEADER IN THE DEVEL-

OPMENT AND MANUFACTURE OF SUPER- BRIGHT LED ARRAYS, LAMINA BRINGS

SOLID STATE LIGHTING TO APPLICATIONS

WHICH UNTIL NOW WERE ONLY POSSIBLE WITH TRADITIONAL LIGHTING SOURCES.

LAMINA'S STANDARD PRODUCTS, AVAIL-

ABLE IN WHITE, RGB AND MONO- CHROME, ARE DESIGNED TO DELIVER

1W TO 100W OF SUPER-BRIGHT LIGHT. IN ADDITION, LAMINA PROVIDES CUS-

TOMIZED LED ARRAYS AND PACKAGE CONFIGURATIONS. APPLICATIONS INCLUDE ARCHITECTURAL LIGHTING, GEN- ERAL ILLUMINATION, AUTOMOTIVE, SIG- NAGE, AND SIGNALING.

LAMINA LED ARRAYS ARE MANUFAC-

TURED BY COMBINING HIGH BRIGHTNESS

LEDS FROM INDUSTRY-LEADING LED

MANUFACTURERS WITH LAMINA'SPRO- PRIETARY PACKAGING TECHNOLOGY, MUL- TILAYER LOW TEMPERATURE CO-FIRED

CERAMIC ON METAL (LTCC-M). LTCCM IS A BREAKTHROUGH IN THERMAL

PERFORMANCE FOR LED PACKAGING TECHNOLOGY, A KEY FACTOR IN DETER- MINING LED LIFE AND RELIABILITY.

UNMATCHED THERMAL PERFORMANCE

COUPLED WITH PACKAGE INTERCONNEC- TIVITY ALLOWS LAMINA TO DENSELY CLUSTER MULTIPLE LEDS TO ACHIEVE EXCEPTIONALLY HIGH LUMINOUS INTENSI- TY IN VERY SMALL FOOTPRINTS.

Solid state lighting, in the form of light emitting diodes (LEDs), has many advantages over traditional light sources, such as longer life, new form factors, and higher efficiencies. These advantages make LEDs attractive for many new applications. At the same time, LEDs present several unique challenges to lighting designers and users in management of thermal energy created in LEDs.

This application note describes basic thermal management which must be undertaken by users of Lamina's Solid State Light Engines. Inadequate thermal design can result in diminished light output, reduced life, higher power consumption and be a hazard to personal safety. This application note is not intended to be a comprehensive thermal design tool, but to provide a guide to our customers. For additional support in your thermal designs, please contact Lamina's Application Engineering Department.

INTRODUCTION

In traditional light sources such as incandescent or fluorescent, much of the energy lost in generating visible light is dissipated as heat in the radiant beam of light. Fixtures surrounding these traditional light sources such as shade or reflectors, or surfaces illuminated by these sources can and will experience thermal rise above ambient, depending on the efficiency and intensity of the light (i.e. Power) source used. Solid State Lighting (LED's) is more efficient at generating visible light than many "filament" type light sources. However, the heat energy developed during operation of LEDs does not radiate away from the LED in the light beam area, but conducts back through the semiconductor, into the package material and heatsink.

Lamina utilizes a patented semiconductor packaging technology that is extremely efficient at removing thermal energy (i.e., low thermal resistance from Junction to Case) from the semiconductor and transferring it into a heatsink. This packaging technology has been in successful use in numerous high power and high density power modules and packages in excess of 100 watts for several years.

Lamina's unique Light Engine products achieve the highest lighting density of Solid State devices with values exceeding 1400 lumen per square inch. Achieving these high densities and high light output values requires the user to carefully plan the thermal management as a "System" considering not only the light source, but the heatsink and thermal interface materials used in the design.

In proper thermal management, the goal is to provide the minimum path of thermal resistance from the Semiconductor (LED) junction to the heatsink. AIR represents among the HIGHEST of thermal resistances, therefore any adequate thermal design will eliminate air from the thermal chain.

AIR is the enemy of proper thermal management.

Bright Lights. Bright Ideas.

APPLICATION NOTE 02

HEATSINK REQUIREMENTS

Lamina's Light Engine consists of a highly dense array of LEDs arranged into an LTCC-M packaging system. The LED die are directly bonded to the "Case" or the Cu/Mo/Cu base of the light engine. By directly bonding the die to the case, the minimum thermal resistance between the die junction and case is achieved. Lamina's products contain either a Ag/Pd (Silver Palladium) solderable layer on the back of the case to facilitate solder bonding to a heatsink, or flange-mount features created into the case design to facilitate screw-down applications.

Applications using Lamina's Light Engines MUST be properly mounted to a heatsink prior to operation or light up. The Light Engine case IS NOT a thermal heatsink. It is utilized for efficient transfer of thermal energy into a properly designed heatsink. Energy should not be applied to Lamina's light engines without a heatsink for more than a fraction of a second, or the thermal energy created can permanently damage the light engine.

Lamina has worked closely with several heatsink manufactures to create basic and Minimal heatsinks that will allow the connection and utilization of our products in your designs. While these designs may not be applicable for all applications, they will enable you to create your design concepts, with minimal investment in time or resources. Heatsink suppliers can and often times do, manufacture custom heatsinks to meet your specific needs. Links to these resources are contained at the end of this paper.

THERMAL DESIGN

Thermal Design goes far beyond the basics concepts of thermal modeling. Lamina's Light Engines have small, flat form factors that allow designers to creative aesthetic thermal designs for reflectors, shrouds or fixtures. The first step in this process is to understand and use thermal modeling in your design.

Thermal Modeling can be understood in the most basic concept which is to predict the Junction Temperature, Tjunction (called the N-P junction in semiconductor devices) where the light is generated. Solid State light quality is highly dependent upon Tjunction. Figures 1 and 2 illustrate the behavior of Solid State lighting with increasing Junction Temperature.

Figure 1. Junction Temperature effect on Light Output

Figure 2. Junction Temperature effect on Light Color

Durgin et.al. Dialight Corp 2003

Figures 1 and 2 illustrate the sensitivity of LED's to junction tem- perature. As is evident in Figure 1, higher junction temperatures lead to lower light output, with Red and Amber the most affected. Figure 2 shows the effects of LED junction temperature on color (Wavelength). Green LED's are the most affected. Proper thermal management can minimize these effects.

The primary purpose of Thermal Modeling is to select the characteristics of a heatsink and thermal interface material that allow you to maintain the Junction Temperature within your design limits.

While there are several analytical modeling and simulation tools available for Thermal Design, they are primarily used in the optimization of the light engine or the heatsink once the basic parameters are selected. Understanding the Thermal Resistance of a product, AND the relationship of that thermal resistance to the thermal resistance values of the other elements in the thermal chain is the most basic skill required.

Thermal Resistance is calculated by dividing the difference in temperature between two points on a body by the energy that flows between those points per unit time. Thermal Resistance can be expressed by the following equations:

L ∆T

RΘ = ----------- -or- RΘ = ----------

K • A Q

Where: RΘ = Thermal Resistance L = Distance from thermal source K = Value of Thermal Conductivity

(A material property which can be found in suppliers data)

A = Cross-sectional Are a of the heat source ∆T = Change in Temperature from heat source to area of interest Q = Heat Flux (or dissipated power in Watts)

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