MAGIC LED PLW114050 Series
Application Note
Thermal Management
Solid-state light emitting diodes (LED) are highly efficient and reliable when
compared with traditional light source technologies. Their long-term reliability
performance depends highly on maintaining the operating conditions within the
datasheet recommendations. Although today LEDs are very efficient, a considerable
amount of the electrical input power is still not converted into light but simply lost and
transformed into heat. Unfortunately, the heat generated inside the LED impacts
negatively on its performance and in extreme cases can even cause catastrophic
failure. The LEDs are designed to dissipate heat efficiently but users need to make
sure the LEDs are operating within specification. The performance of Plessey LED
is characterized versus its junction temperature Tj. The junction temperature can not
be measured directly and therefore it is calculated using equation (1) below;
T
j
= T
a
+ (Rө
j-sp
+ Rө
sp-hs
+ Rө
hs-a
)
*
(V
f *
I
f
– W
op
)
(1)
Where,
T
j
is the junction temperature in degrees Celsius (°C)
T
a
is the ambient temperature (°C)
Rө
j-sp
is the thermal resistance between junction and solder point (°C/W)
Rө
sp-hs
is the thermal resistance of the PCB heat sink (°C/W)
Rө
hs-a
is the thermal resistance between PCB heat sink and ambient (°C/W)
I
f
is the forward current and V
f
is forward voltage.
W
op
is the optical radiant power (W).
Therefore, a good thermal dissipation design consists of minimizing both thermal
resistances Rө
sp-hs
and Rө
hs-a
achieved by optimising the heat conduction path.
PLESSEY| TAMERTON ROAD | ROBOROUGH | PLYMOUTH | DEVON | PL6 7BQ
Phone: +44 1752 693000
Datasheet No 292552 Issue 1
Fax: +44 1752 693200
Page
1
of
3
Web: www.plesseysemi.com
Handling Precautions
Compared to epoxy encapsulate that is hard and brittle, silicone is softer and flexible.
Although its characteristic significantly reduces thermal stress, it is more susceptible
to damage by external mechanical force. As a result, special handling precautions
need to be observed during assembly using silicon encapsulated LED products,
failure to comply might lead to damage and premature failure of the LED.
1. Handle the component along the side surface by using forceps or appropriate
tools; do not directly touch or handle the silicone lens surface; it may damage the
internal bond wire.
2. The outer diameter of the SMD pickup nozzle should not exceed the size of the
LED to prevent air leaks. The inner diameter of the nozzle should be as large as
possible. The nozzle should preferably be made of soft and elastic material to
prevent scratching or damaging the LED surface during pickup. The dimensions of
the component must be accurately programmed in the pick-and-place machine to
insure precise pickup and avoid damage during production.
Electrostatic Discharge and Electrical Overstress
Plessey LEDs are not designed to operate with reverse bias. Precautions are
required to prevent reverse bias in applications and during handling. Electrostatic
discharge (ESD) or electrical overstress (EOS) may damage LEDs. Precautions
such as ESD wrist straps, ESD shoe straps or antistatic gloves must be worn
whenever handling the LEDs. All devices, equipment and machinery must be
properly grounded. It is recommended to perform electrical tests to screen out ESD
failures at final inspection. It is important to eliminate the possibility of electrical
overstress during circuitry design.
PLESSEY| TAMERTON ROAD | ROBOROUGH | PLYMOUTH | DEVON | PL6 7BQ
Phone: +44 1752 693000
Datasheet No 292552 Issue 1
Fax: +44 1752 693200
Page
2
of
3
Web: www.plesseysemi.com
Evaluation Board
FR4 evaluation boards are available on request. Please contact Plessey sales team
for further information.
Recommended solder-pad design for heat dissipation:
Note: Metal (copper) area at 1 should not be less than 50mm
2
for sufficient heat
dissipation while area 2 and 3 should not be less than 5mm
2
.
PLESSEY| TAMERTON ROAD | ROBOROUGH | PLYMOUTH | DEVON | PL6 7BQ
Phone: +44 1752 693000
Datasheet No 292552 Issue 1
Fax: +44 1752 693200
Page
3
of
3
Web: www.plesseysemi.com
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