Recommended Design Practices for
Proper Thermal Management
PCB Design
Proper PCB design can reduce the
R
θ
ja
of a
LED lamp assembly, and thus reduce the
junction temperature of the LEDs. Listed below
are some recommended practices for the
design of LED PCBs.
Maximum Metallization
Conventional PCB design involves connecting
various points on the board with traces of
sufficient width to handle the current load. This
process is usually visualized as adding traces to
a blank PCB. For LED PCBs, this process
should be reversed—visualized as removing
metal only where needed to form the electrical
circuit. Large metal pads surrounding the
Figure 4.4 Graph of HPWT-xxOO Derating Curves.
cathode leads of the LEDs are ideal. Very little
heat is conducted through the anode leads of
the LED, so additional metallization surrounding
these leads does not help.
Table 4.3
Typical T
a (max)
Values for Automotive Signal Lamps
Application
Exterior-mounted signal lamp
Interior-mounted CHMSL
Interior, head-liner mounted CHMSL
Typical T
a (max)
(°C)
70
80
90
Figure 4.5 Relative Luminous Flux vs. Forward
Current.
Figure 4.6 LED CHMSL PCB with proper
metallization and component placement.
8
LUMILEDS [ LUMILEDS LIGHTING COMPANY ]
