CL-L102 Datasheet, PDF (1/3 Pages) CITIZEN ELECTRONICS CO., LTD. – LED lamp

Thermal Management of CL-L102
1. Introduction
The light-emitting element of an LED radiates light and heat according to the input power. However,
the surface area of an LED package is quite small and the package itself is expected to release little
heat to the atmosphere. An external radiator such as heat sinks is thus required. The heat release
configuration for the connection portion of the external radiator mainly uses heat conduction.
Regarding LED packages, to control the junction temperature of the light-emitting element Tj is
important. Tj must be kept from exceeding the absolute maximum rating in the specifications under any
condition. Because direct measurement of the junction temperature of a light-emitting element inside a
package is seldom possible, the temperature of a particular part on the package outer shell (the case
temperature) Tc [deg C] is normally measured. Tj [deg C] is calculated from the thermal resistance
between the junction and the case, Rj-c [deg C/W] and the amount of emitted heat, which is nearly
equal to the input power Pd [W]. The package structure of the CL-L102 series minimizes the thermal
resistance Rj-c, and the heat generated at the light-emitting element can be conducted to the external
radiator efficiently.
This document describes the detailed heat release configuration of the CL-L102 series and provides
necessary data for thermal design of lighting apparatus, which leads to optimal utilization of LED
performance.
2. Package configuration and thermal resistance
Fig. 1 (a) illustrates the example of the
cross-section structure where the
package of the CL-L102 series is
connected to an external heat sink. The
package is composed of an aluminum
substrate and the laminated structure of
insulating layers and conductive copper
foil patterns.
A distinctive point is the light-emitting
element is not mounted on the insulating
layer, which has low thermal conductivity
but directly on the well conductive
Fig. 1 (a)
Fig. 1 (b)
aluminum substrate. Thus, the heat
generated at the light-emitting element can be efficiently conducted to the outside of the package.
The aluminum substrate side of the package outer shell thermally connects to the heat sink via
heat-dissipative grease (or adhesive). As described above, the heat generated in the junction section of
the light-emitting element is mainly transferred as conductive heat from the light-emitting element via
element-mount adhesive, the aluminum substrate, and grease (adhesive) to the heat sink. The thermal
resistance from the junction section of the light-emitting element to the aluminum substrate side of the
package outer shell is Rj-c, which is the specific thermal resistance value of the package. Hence, the
following equation makes sense.
Tj = Rj-c x Pd + Tc
In addition, the thermal resistance of the grease (adhesive) outside of the package is Rb [deg C/W],
that of the heat sink is Rh [deg C/W], and the ambient temperature is Ta [deg C].
Fig. 1 (b) shows the equivalent thermal resistance along the cross-section diagram on Fig. 1 (a). The
thermal resistances Rj-c, Rb, and Rh are connected in series between the junction temperature Tj and
the ambient temperature Ta. Now the thermal resistances outside the package Rb and Rh can be
integrated into the thermal resistance Rc-a, which leads to the following equation.
Tj = (Rj-c + Rc-a) x Pd + Ta
ï¼²ef.CE-P471 04/09