LAMINA THERMAL MANAGEMENT User Manual
Bright Lights. Bright Ideas.
TM
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.
2
Bright Lights. Bright Ideas.
TM
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
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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