LX_M&S_FE005
High efficiency digital light source
(actual size)
Thermal Management
nanoXED
Contents
1.) General……………………………………….… page
2.) Mounting Instructions…….………………….. page
3.) Significant parameters.……………………….. page
4.) Worst case analysis.………………………….. page
5.) Thermal Management influence factors..…… page
6.) Summary……………………………………….. page
2
2
4
5
7
9
Rev.00 (11/07)
nanoXED-Thermomanagement-rev00.doc
Page 1/10
High efficiency digital light source
1.) General:
The rated life of the nanoXED products depends to a large extent on the operating
temperature of the device. If the permissible temperature limits are exceeded, the life of the
nanoXED will be greatly reduced or the nanoXED may be damaged.
Maximum Temperature Values:
Junction Temperature
Ambient Temperature
Storage Temperature
Soldering Temperature (for max. 10s)
+140
+115
+115
+260
Tj max
Ta max
Tstg max
Tsld max
°C
°C
°C
°C
Table 1
For the Thermal Management these values have to be considered.
2.) Mounting Instructions:
The nanoXED component has to be soldered by a reflow process onto a PCB (dimensions
of the foot-print shown in Fig.1).
Anode
Cathode
Unit: mm
Fig.1: Recommended dimensions of foot-print
The solder pad should be close to the electrode area, as recommended. The larger the
metal area underneath the solder resist, the better the heat transfer.
nanoXED-Thermomanagement-rev00.doc
Page 2/10
High efficiency digital light source
Recommended soldering conditions (surface of circuit board) –lead-free solder
Maximum soldering profile
260 °C for max. 10 s
1 ~ 3°C/sec.
Recommended soldering profile
250 °C for max. 15 s
Minimum soldering profile
240 °C for max. 20 s
Preheating
180 ~ 200°C
60sec. max.
above 220°C
1 ~ 3°C/sec.
120sec. max.
Fig.2: Recommended soldering conditions
Substrate materials:
Note1
Metal Core PCB (integrates a base metal material as heat spreader).
Standard FR4-PCB with thermal vias (ref. fig. 5 and 6) Note 1.
Flexible PCB (thinner dielectric layer than standard one)
Patent of TridonicAtco Optoelectronics GmbH for Germany and Austria – Nr. 203 07 468.8
To achieve a high thermal conductivity through the PCB, a metal core (e.g. aluminium)
substrate with 75µm dielectric layer having a thermal conductivity > 0,9 W/mK recommended.
To increase the thermal conductivity further the PCB surface should be covered with copper
as much as possible. (ref. to Fig. 3).
Depending on the operating conditions, the PCB with the soldered component has to be
installed either on a heat sink or aluminium plate with a thermally conductive adhesive. To
ensure permanent adhesion the relevant surface of the heat sink and PCB must be cleaned
(remove all dirt, dust and grease) before applying the adhesive layer.
Recommendation of cleaning fluid: Acetone. For a complete design refer to Fig. 3.
Molding compound
Contact leads
case
Solder
Thermal adhesive layer
Solder pad
Fig. 3: Design of complete Package
Heat sink
PCB
Fig.3: nanoXED thermal design
nanoXED-Thermomanagement-rev00.doc
Page 3/10
High efficiency digital light source
3.) Significant parameters:
To keep the junction temperature below Tjmax a suitable thermal design is necessary.
nanoXED must be operated within following maximum ratings:
Power Input: P max= 0,95W
DC Forward Current: If max= 250mA
Junction Temperature: Tj max= 140°C
Ambient Temperature: Ta max= 115°C
Because of the fact that a correct measure of the Junction Temperature is not possible, the
value must be calculated.
Tj = Ta + Rth JA • P
Schematic of the thermal design:
(TJ)
(TS)
(TB)
(TA)
Fig. 4: Design showing the thermal resistance
To achieve a better thermal management, nanoXED has an asymmetric electrode
design. This enables an optimized heat transfer from the chip through the package and to
the solder pad.
Tj
=
=
Ta
Rth JA =
Rth JS =
Rth SB =
Rth BA =
P
=
Junction Temperature: [°C]
Ambient Temperature: [°C]
Thermal resistance from XED Junction to Ambient: [K/W]
Thermal resistance from XED Junction to Solder Point: [K/W]
Thermal resistance from XED Solder Point to Board: [K/W]
Thermal resistance from XED Board to Ambient: [K/W]
Input Power (IF ∗ VF) : [W]
nanoXED-Thermomanagement-rev00.doc
Page 4/10
High efficiency digital light source
4.) Worst case analysis:
The following example shows the minimum rating of the heat sink at Tj max and highest
operating conditions using a defined metal core PCB. Refer to Fig. 4 for details.
Given Parameters:
Max. Junction Temperature:
Max. Power Input:
Max. DC Forward Current:
Max. Ambient Temperature
Max. Thermal Resistance Junction-Solder Point:
Typ. Thermal Resistance from PCB *)
Tj max
Pmax
If max
Ta
Rth JS
Rth SB
140
0,95
250
115
12
5
°C
W
mA
°C
K/W
K/W
Table 2
*) The typical value for RthSB = 5 K/W considering following data:
Aluminium core PCB 20x20x1.5mm with 75µm dielectric layer,
Thermal conductivity of dielectric layer: 0,9 W/mK
Foot pad size: 2x (6x3mm)
One can calculate the minimum required heat sink characterized as follows by RthBA.
Calculating Parameters:
Thermal Resistance Heat Sink-Ambient:
Rth BA
(1)
The junction temperature can be calculated by the following equation:
⇒ Tj = Ta + Rth JA∗Pmax
(2)
Inserting the value from table 2:
⇒ Rth JA min = (Tj – Ta) / Pmax = (140 – 115) / 0,95 = 26 K/W
(3)
The thermal resistance from junction to ambient follows out the addition of the
respective thermal resistance:
⇒ Rth JA min = Rth JS + Rth SB +Rth BA
(4) Rearranging equation for Rth JA and inserting example data:
⇒ Rth BA= Rth JA – (Rth JS + Rth SB) = 26 – (12 + 5) = 9 K/W
Rth BA = 9 K/W
This is the absolute minimum rating of the heat sink. It is recommended to cross check
the calculation for standard operating conditions.
nanoXED-Thermomanagement-rev00.doc
Page 5/10
High efficiency digital light source
Ts point and ambient temperature Ta
The temperature at Ts reference point is crucial for the light output and lifetime of a XED.
It is recommended that the Ts temperature of the nano XED never exceed 85 °C, to achieve
an optimum between heat sink requirements, light output and lifetime. Compliance with the
maximum permissible reference temperature at the Ts point (Fig.5) must be checked under
operating conditions in a thermally stable state. The maximum value must be determined
under worst-case conditions for the relevant application.
Calculation is one basis for design of the cooling area.
For release thermal measurement of TS is absolutely necessary.
Cathode
TS point
Anode
Fig.5: Ts reference measurement point on the PCB
nanoXED-Thermomanagement-rev00.doc
Page 6/10
High efficiency digital light source
5.) Thermal Management influencing factors:
There are many factors that can influence the thermal design of the package. It depends
strongly on the application.
Following the main parameters are shown which have to be considered:
Selection of electrical values:
Input Power: Pmax= Uf*If………….(Pmax = 0,95 W)
Heat generation can be reduced by decreasing the input power resp. forward
current.
Selection of the Printed Circuit Board (PCB):
The most critical point of the heat management is the PCB (material with the highest
thermal resistance). To get good heat dissipation you have to choose a PCB with a low
thermal resistance.
All typical PCB material with low thermal resistance (RthSB ≈ 5 K/W) can be used – like
ceramic PCB, metal core PCBs, organic PCBs (FR4 - only be used by considering
special designs, ref. to Fig.6).
Please refer to commercial supplier information.
There are several different materials available on the market (see for example
recommendation section 2).
Design recommendation for organic PCB:
Thermal Vias:
Copper Layer
nanoXED
Thermal Vias
Dielectricum e.g. FR4
Fig. 6: Structure of FR4 PCB with thermal vias and heat sink
nanoXED-Thermomanagement-rev00.doc
Page 7/10
High efficiency digital light source
Reference values for thermal vias:
Solder resist
Via holes
nanoXED
- Via area incl. nanoXED:
approx. 1cm2
- Diameter of holes
approx. 0,3 mm
- Distance between holes
approx. 0,6 mm
- Number of holes
approx. 50 - 100
FR4-Substrate
1cm
1cm
Fig.7: Example: Arrangement of thermal vias
Size: Heat sink area should be at least same size as PCB area.
Copper: Heat spreading improves with thickness of Copper
min. 70 µm Cu.
Basis material (FR4): 1 – 1.5 mm.
Selection of adhesives:
Use adhesive foils or adhesive pastes with good thermal
conductivity.
The surfaces must be cleaned and smooth to avoid air
inclusions.
Apply a high contact pressure to guarantee a good thermal
conductivity. Take care not to damage the nanoXED during this
process step.
Selection of the heat sink:
Use heat sinks of aluminium or copper with a thermal
resistance below your calculated value.
Any recommendation of the thermal design has to be verified by a Ts point
(solder point ref. to Fig. 5) measurement.
nanoXED-Thermomanagement-rev00.doc
Page 8/10
High efficiency digital light source
6.) Summary:
Thermal design of the end product is critical to the performance of the nanoXED. The
heat generation of the nanoXED must be considered when making the system design.
Operate the nanoXED within the maximum ratings given in this specification within any
time.
For safe operation a solder point temperature Ts of not more than 85°C is recommended
under all possible operating conditions.
The relation between allowable current and the ambient temperature is shown in this
diagram:
If [mA]
Rth JA= 65K/W
Ta [°C]
Fig. 8: Allowable current vs. ambient temperature at the nano XED 5700K
The equation below shows the correlation between Tj and Ta.
Tj = Ta + Rth JA∗P
Definitions and Abbreviations:
TJ
TA
RJA
P
=
=
=
=
Junction Temperature: [°C]
Ambient Temperature: [°C]
Thermal resistance from XED Junction to Ambient: [K/W]
Power Input (If ∗ Vf): [W]
Typical Thermal Resistance Junction-Solder Point:
Rth JS typ. = 12 K/W
nanoXED-Thermomanagement-rev00.doc
Page 9/10
High efficiency digital light source
©2007 LEXEDIS Lighting GmbH. All rights reserved.
Company information:
LEXEDIS Lighting GmbH, a joint venture company between TridonicAtco of Austria and
Toyoda Gosei of Japan, invents and produces innovative and high-performance digital light
sources marketed worldwide under the XED brand. Founded in 2005, LEXEDIS is a fastgrowing and customer-oriented company providing advanced opto-semiconductor products
for the advancement of energy-efficient lighting solutions in automotive, general lighting,
industrial and display applications. As the creator of XED technology, LEXEDIS is the
leading company in the development of intelligent light sources.
For technical assistance or the location of your nearest customer-service office
please contact:
LEXEDIS Lighting GmbH
Technologiepark 10
A-8380 Jennersdorf, Austria
Tel: +43 (0)5 9010 650 0
www.lexedis.com
info@lexedis.com
Product specifications are subject to change without notice. XED is a registered trademark
of Lexedis Lighting GmbH in Europe and other countries.
nanoXED-Thermomanagement-rev00.doc
Page 10/10