Application Note Little Star

VISHAY SEMICONDUCTORS
LEDs
Application Note Little Star
Specification, Handling, Thermal Management
and Design-In
Product Specification
The datasheet presents the performance for the Little Star in
tables and diagrams. Brightness group and color are already
defined in the device type name. More details as VF group
and color group, production date can be seen on the label.
20783
A
20784
Introduction
B
20613
C
A) Type of component
B) Manufacturing plant
C) SEL - selection code (bin):
e.g.: DA = code for luminous intensity group
5 = code for color group
4 = code for forward voltage
D) Batch:
200707 = year 2007, week 07
PH19 = plant code
E) Total quantity
For any questions, contact: LED@vishay.com
Fig. 1 - Design of the Label
APPLICATION NOTE
The Little Star package is designed for high current
application up to 400 mA, with a super high flux output and
presented in a compact package outline. (6.0 x 6.0 x 1.5).
With its low package height of 1.5 mm it presents the best
combination of compactness and highest brightness.
The following application note details product specification
in corresponding data sheets for the different series of the
product.
The InGaN based devices are casted with silicone. Silicone
casting has big advantages in terms of optical stability and
stress relief, but requires a special handling procedure in
assembly.
For the solder process there is no special requirement. The
device is compatible to the existing SMT processes and
standard IR-reflow.
Manual solder process is only accepted for engineering
purposes and de-soldering for failure analysis. Special
conditions are recommended to avoid thermal damage.
Optical parameters especially for InGaN based devices are
strongly temperature dependent.
As a summary beside the handling recommendation a
proper thermal management of is the most important part for
the design in of high power LED. Driving the LED a high
portion of the electrical energy will be converted to heat.
This heat conducts from the junction area through the LED
die, then trough the package and finally to the ambient via
the heatsink. The following application note describes all
this phenomena in detail and gives the necessary
instructions for a efficient application and a long LED life
time.
Document Number: 81897
Revision: 1.0, 01-Jul-08
D
E
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Application Note Little Star
Vishay Semiconductors
Specification, Handling, Thermal Management
and Design-In
LUMINOUS INTENSITY/FLUX CLASSIFICATION RED/AMBER/YELLOW
LUMINOUS FLUX ΦV (MLM)
CORRELATION TABLE
LUMINOUS INTENSITY IV (mcd)
GROUP
STANDARD
MIN.
MAX.
MIN.
MAX.
AA
7150
9000
20 700
26 100
AB
9000
11 250
26 100
33 000
AC
11 250
14 000
33 000
39 000
AD
14 000
18 000
39 000
52 000
AE
18 000
22 400
52 000
71 000
AF
22 400
28 500
71 000
97 000
Note:
Luminous intensity is tested at a current pulse duration of 25 ms and an accuracy of ± 11 %.
The above type numbers represent the order groups which include only a few brightness groups. Only one group will be shipped on each reel
(there will be no mixing of two groups on each reel).
In order to ensure availability, single brightness groups will not be orderable.
In a similar manner for colors where wavelength groups are measured and binned, single wavelength groups will be shipped in any one reel.
In order to ensure availability, single wavelength groups will not be orderable.
COLOR CLASSIFICATION
DOM. WAVELENGTH (nm)
GROUP
DOM. WAVELENGTH (nm)
YELLOW
AMBER
MIN.
MAX.
MIN.
MAX.
A
585
588
610
616
B
588
591
616
620
C
591
594
D
594
597
Note:
Wavelengths are tested at a current pulse duration of 25 ms and an accuracy of ± 1 nm.
FORWARD VOLTAGE CLASSIFICATION
FORWARD VOLTAGE (V)
GROUP
MIN.
MAX.
02
2.2
2.5
03
2.5
2.8
Note:
Forward voltages are tested at a current pulse duration of 25 ms and a tolerance of ± 0.05 V.
In order to ensure availability, a single forward voltage group can not be ordered.
Fig. 2 - Classification Table for brightness, Color and VF
C
B
Y3
A
Y3
Y3
X3
X2
0.49
0.47
0.45
0.43
0.41
0.39
0.37
0.35
0.33
0.31
0.29
X1
0.27
0.48
0.46
0.44
0.42
0.40
0.38
0.36
0.34
0.32
0.30
0.28
0.26
0.24
0.22
0.25
Cy
APPLICATION NOTE
Handling Procedure
Chromaticity Coordinate Groups for
Warm White SMD LED
Cx
Fig. 3 - Color Grouping on White and Warm-White
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The Little star package is, as all platic packages, humidity
sensitive. The Jedec level 2a is specified. This means the
floortime is 672 h in an environment of 10 °C to 30 °C and
humidity < 60 % RH.
After more than 672 h under these conditions moisture
content will be too high for reflow soldering. In case of
moisture absorption, the devices will recover to the former
condition by drying under the following condition:
192 h at 40 °C + 5 °C/- 0 °C and < 5 % RH (dry air/nitrogen)
or
96 h at 60 °C + 5 °C and < 5 % RH for all device containers
or
24 h at 100 °C + 5 °C not suitable for reel or tubes.
For any questions, contact: LED@vishay.com
Document Number: 81897
Revision: 1.0, 01-Jul-08
Application Note Little Star
Vishay Semiconductors
Specification, Handling, Thermal Management
and Design-In
AlInGaP based devices as red, amber and yellow are casted
with clear resin. There is no special requirement for
mechhanical handling. For InGan based devices, especially
for the white silicone is used as encapsulant. The advantage
of silicone is the thermal and photo stability in a variety of
harsch environment. This features minimize the risk of
yellowing or changing in physical properties during device
operation. As a result of the advantages of a silicone
encapsulant the lifetime of the LED can be increased up to
100 kh.
On the other side silicone is much softer compared to epoxy
resin. Thus, when handling the LED, care should be taken
not to apply excessive pressure on top of the silicone. Sharp
objects might pierce through the silicone encapsulant and
damage the LED.
When handling the LED using tweezers, care should be
taken to ensure that the tweezers would not be in contact
with the silicone surface to prevent scratches on the lens.
The right way to pick or place the LED using tweezers from
the side of the package as shown in Fig. 4.
Fig. 5 - Acceptable Foreign Particle Level on a Silicone Casted LED
Optical and Electrical Charactersistics Across
Operation Temperature Range
The optical and electrical characteristic of a power LED
depends strongly on the junction temperature.
The forward voltage decreases while the dominant
wavelengths increases with the temperature, as shown in
fig. 6 to 8 for AlInGaP and InGaN based devices.
Rel. VF vs. Ambient Temperature
IF = 400 mA
1.5
1.4
1.3
VF rel
red
1.2
amber
1.1
yellow
1.0
0.9
0.8
- 40
- 20
Fig. 4 - Requirement for Manual Handling
Document Number: 81897
Revision: 1.0, 01-Jul-08
25
50
100
Fig. 6 - VF over Temperature for AllnGaP Based Devices
Rel. LD vs. Ambient Temperature
IF = 400mA
10
8
yellow
6
LD/nm
4
red
2
0
-2
-4
-6
amber
-8
- 10
- 40
- 20
0
25
50
100
Temperature (°C)
Fig. 7 - Dominant Wavelength vs. Ambient Temperature
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APPLICATION NOTE
For SMT mounting, the pick and place nozzle use must be
bigger than the LED emission area, to prevent the LED from
sticking to the pick and place nozzle. Parameter settings for
pick and place process should also be evaluated to ensure no
damage to the LED's.
If cleaning is required after soldering, we suggest to use IPA
as cleaning agent. Maximum recommended rinsing time is
10 s. No use of ultrasonic to avoid damages during cleaning.
Due to the silicone is soft in nature; the tendency of foreign
particulate to adhere on the silicone surface would be greater
compared to epoxy resin. A certain amount of particles can
be accepted without influencing the performance of the
LED.
Typical contamination in an acceptable range is shown in
fig. 5
0
Temperature (°C)
Application Note Little Star
Vishay Semiconductors
Specification, Handling, Thermal Management
and Design-In
Change of x/y vs. Ambient Temperature
White IF = 350 mA
Rel. Iv vs. Ambient Temperature
IF = 400 mA
2.5
0.05
0.04
yellow
2.0
0.03
0.02
dx/dy
amber
lv rel
1.5
red
0.01
0.00
- 0.01
1.0
- 0.02
- 0.03
0.5
- 0.04
0.0
- 0.05
- 40
- 20
0
25
50
100
- 40
- 20
Fig. 8 - Relative Luminous Intensity vs. Ambient Temperature
1.15
1.10
VF rel
1.05
1.00
0.95
0.90
0.85
- 20
0
25
50
100
Temperature (°C)
Fig. 9 - VF vs. Ambient Temperature for White
Rel. Luminous Intesity vs. Ambient Temperature
White IF = 350 mA
Rel. Iv vs. Forward Current
1.8
1.6
1.0
1.4
0.9
1.2
lv rel
lv rel
1.1
APPLICATION NOTE
0.8
0.7
red
amber
yellow
1.0
0.8
0.6
0.6
0.4
0.2
- 40
- 20
0
25
50
100
Temperature (°C)
0.0
0
Fig. 10 - Relative Luminous Intensity vs. Ambient Temperature
for White
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100
The dominant wavelength is a function of the junction
temperature and therefore also a function of the forward
current applied to the LED due to a part of energy converted
to heat.
The typical relationship between the forward current change
versus the wavelengths or CxCy shift is shown in fig. 13, 15.
For unique illumination of an area the individual device is
driven by different brightness and therefore with different
current. This will shift the dominant wavelengths and
therefore also the color. In applications where this shift can
not be tolerated, pulse width modulation (PWM) should be
used to dim the brightness. The frequency of PWM should
be above 200 Hz, so that the human eye can not follow the
on/off cycle. The colour shift can be avoided by PWM
(fig. 16).
1.2
0.5
50
Dimming the Little Star
1.20
- 40
25
Fig. 11 - Color Coordinates x, y vs. Ambient Temperature
Rel.VF vs. Ambient Temperature
White IF = 350 mA
0.80
0
Temperature (°C)
Temperature (°C)
200
400
600
800
1000
IF (mA)
Fig. 12 - LOP vs. Forward Current
For any questions, contact: LED@vishay.com
Document Number: 81897
Revision: 1.0, 01-Jul-08
Application Note Little Star
Vishay Semiconductors
Specification, Handling, Thermal Management
and Design-In
Relative Luminous Intensity IVrel
vs. Duty Cycle
Rel. LD vs. Forward Current
4.0
1.2
3.0
1.0
2.0
amber
LD (nm)
1.0
0.8
red
Iv rel
0.0
0.6
- 1.0
yellow
0.4
- 2.0
- 3.0
0.2
- 4.0
0
200
400
600
800
1000
IF (mA)
Fig. 13 - Dominant Wavelength vs. Forward Current
0.0
0
20
40
60
80
Duty Cycle (%)
100
120
Fig. 16 - Relative Luminous Intensity vs. Duty Cycle
Rel. Luminous Intensity vs. Forward Current
White
Thermal Management
2.5
Driving an LED part of the power is converted to light. The
major part of the energy is converted to heat. This heat
generated at the PN junction has to be transferred out of the
LED through the package to the PCB and from there to the
local ambient as shown in fig. 17 and 18.
2.0
lv rel
1.5
1.0
0.5
0.0
0
200
400
600
800
1000
IF (mA)
Fig. 14 - White: Luminous Intensity vs. Forward Current
Change of x, y vs. Forward Current
White
0.010
0.008
Fig. 17 - The Way the Heat Goes out of the LED via Leadframe to
0.006
the PCB
dx, dy (ccd)
0.004
0.002
0.000
- 0.002
- 0.004
- 0.008
- 0.010
0
200
400
600
800
1000
IF (mA)
Fig. 15 - White: X, Y vs. Forward Current
Fig. 18 - The Thermal Resistance Rthja as a Summary of Individual
Parts
Document Number: 81897
Revision: 1.0, 01-Jul-08
For any questions, contact: LED@vishay.com
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APPLICATION NOTE
- 0.006
Application Note Little Star
Vishay Semiconductors
Specification, Handling, Thermal Management
and Design-In
The heat transfer out of the system described in fig 17 is
following "Ohm's Thermal Law"
(1)
Tj = LED junction temperature
Ta = Ambient temperature
Rthja = Thermal resistance junction to ambient
VF = Forward voltage
90
Thermal Resistance (K/W)
Tj = Ta + Rthja x (VF x IF)
100
IF = Forward current
80
70
60
50
40
Rthja (°C/W)
30
20
Rthjs (°C/W)
10
Out of the summary of individual parts to total thermal
resistance
0
0
1000
2000
3000
4000
5000
MC PCB Size (mm x mm)
Rthja = Rthjs + Rthsa
(2)
Fig. 20 - Effect of Heat sink size on Rthjs and Rthja
Rthjs = Thermal resistance junction to solder point
Solder Requirements
Rthsa = Thermal resistance solder point to ambient
From "ohm's thermal law"
Tj - Ts = Rthjs x (VF x IF)
(3)
or
Tj = Rthjs x (VF x IF) + Ts
(4)
Ts = Solder temperature
Equation (4) is particular important in practical calculation
to ensure under specific operating condition, the junction
temperature will not exceed absolute maximum Tj rating
defined in the datasheet.
The Ts can be measured by soldering a thermocouple to the
solder-point.
Theoretically the thermal resistance junction to solder point
is solely a function of the component package. In practical
the junction to solder point resistance will vary with the
different cooling environment. Measurements are shown in
fig. 19 and 20.
The soldering surfaces are plated 100 % pure Sn. The
component is designed to be compatible to the existing
industry SMT process and IR-reflow. There are no special
processes or equipment required for the mounting of the
components in different applications. Both the thermal and
electrical connections are provided by the conventional
process. Therefore, there is no need to provide for additional
process or material to take care for the thermal connection.
However, due to the unique design, all the soldering
terminals are located at the bottom surface of the
component. This greatly reduces the space required and also
enhances the thermal dissipation capability of the
component. Heat from the LED chip is directly conducted
via the soldering terminals to the external environment.
Thermal path is kept to the very minimum.
As for the soldering process, the component is qualified for
both Pb and lead (Pb)-free soldering profile. Both profiles as
described in the datasheet are applicable.
140
948625
300
max. 240 °C
10 s
ca. 230 °C
250
100
Temperature (°C)
Temperature (°C)
APPLICATION NOTE
120
80
Tj at 350 mA (°C)
60
40
215 °C
150
max 40 s
max. 160 °C
100
90 s to 120 s
Ts at 350 mA (°C)
20
200
Lead Temperature
50
Full Line: Typical
Dotted: Process Limits
2 K/s to 4 K/s
0
0
0
1000
2000
3000
4000
5000
0
50
100
150
200
250
Time (s)
MC PCB Size (mm x mm)
Fig. 19 - The Effect of Heat Sink Size on Junction and Solder Point
Fig. 21 - Recommended Lead (Pb)-free IR-reflow Profile for
Temperature
Lead (Pb)-free Soldering
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For any questions, contact: LED@vishay.com
Document Number: 81897
Revision: 1.0, 01-Jul-08
Application Note Little Star
Vishay Semiconductors
Specification, Handling, Thermal Management
and Design-In
Manual Soldering
IR Reflow Soldering Profile for Lead (Pb)-free Soldering
Preconditioning acc. to JEDEC Level 2a
300
Temperature (°C)
max. 260 °C
245 °C
255 °C
240 °C
217 °C
250
200
The device is not released for manual solder process due to
undefined heat load. Therefore manual solder or de-solder
process should be limited to failure analysis and R & D
applications.
max. 30 s
150
max. 100 s
max. 120 s
100
max. ramp up 3 °C/s
50
max. ramp down 6 °C/s
0
0
50
19885
100
150
Time (s)
200
250
300
max. 2 cycles allowed
Fig. 22 - Recommended SnPb IR-reflow Soldering Profile
APPLICATION NOTE
Document Number: 81897
Revision: 1.0, 01-Jul-08
For any questions, contact: LED@vishay.com
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7