LED Cooling Variations: Chip On Board, LED-On-Board

LED Cooling Variations:
Chip On Board, LED-On-Board and
Driver-On-Board
LED Event Telerex
Norbert Engelberts (Founder & CEO)
Optimal Thermal Solutions B.V.
Overview
•
•
•
•
Introduction
Examples of LEDs single & multichip
LED on Board, Chip on Board, Diver on Board
Differences in Light engines
–
–
–
–
LED on board
Chip on Board
Multichip on board
Carriers
• FR4 pcb
• MCPCB FR4 based & enhanced
• Ceramic
• Interfacing with heat sink
• Conclusion
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2
Examples Of LED Solutions
Single & Multichip Solutions - COB
Source: Cree, Osram, Citizen, Lumileds
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3
COB, LED on Board, LED with Driver
on Board (AC&DC)
1. What are the
differences thermally
2. What is important
3. How to optimize
Source: GE Infusion
DLM3000, If,max
1400mA
Source: OSRAM PL-CORE
Z3 5000-930, If,max 1600mA
Source: OSRAM
PL-CORE
AC2000-827,
Inom, ac 130mA
Lucent LED70
If,max 1000mA (34W)
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Lucent LED50
If,max 700mA (20W)
4
Examples Of LED Solutions
Thermal resistance over time
Thermal resistance of LED package
300
250
250
Rth [K/W]
200
150
125
100
75
50
15
0
1965
1970
1975
1980
1985
1990
1995
7
2000
5
2005
0.4 0.19
2010
2015
2020
Year
Source: Thermal Management for LED Applications figure 2.19,
with courtesy of Cree & Schubert EF & Lumileds
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5
Examples Of LED Solutions
Typical thermal resistances
Cree
Color
White (cool, neutral,warm)
Blue
Green
Amber, red, red-orange
Lumiled
L2CI- LHC1XM-L
Luxe xxxx1 xxxxXP-C XP-E XP-G XM-L EZW MX-3 MX-6 ML-B ML-ELuxeon Aon Tx 20206 1202
12
9
6
2.5
3
11
5
25
11
6
3
0.98 0.67
12
9
20
15
15
10
LHC1xxxx1211
0.19
Source: with courtesy of Cree & Lumileds
Material
FR4
Copper
Ceramic
Solderpaste
Aluminum Nitride
FR4 Prepreg
Epoxy
enhanced prepreg
Via
conductivity typical thickness
[W/mK]
[um]
0.3
800-1600
385
18-35-70-105
16
50
150
170
0.3
60-100
0.3
3
100
385
25-35
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6
Differences in Light Engines
Single die leaded LED package
on a FR4 board
Phosphor(s)
Lens
Bond wire
LED(s)
Slug
Lead
Solder paste
Copper
PCB
TIM
HS
Vias
•
•
•
•
•
Plastic package with in the centre bottom a copper/ aluminium slug
Die attached to the slug and wire bonded to a lead-frame LED
devices are highly complex devices.
Slug and leads soldered with solder paste top board
To model such a complex device, a lot of detail knowledge, time and
effort would need to go into modelling the device.
The junction to slug/thermal pad thermal resistance is given by LED
supplier the Rj-s but the actual thermal model is much more complex
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Differences in Light Engines
Single Die Ceramic package
on a FR4
Phosphor(s)
Lens
LED(s)
Bond wire
Ceramic substrate
Path
Copper
PCB
TIM
HS
Vias
• Ceramic carrier with a two connections paths and a centre
path for cooling. Die attached to the ceramic and wire bonded
to the paths
• The package is placed with solder paste to the board
• The junction to slug/thermal pad thermal resistance is given
by LED supplier the Rj-s but the actual thermal model is much
more complex see schematic
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8
Differences in Light Engines
Chip on Board
on Metal Core PCB
Phosphor(s)
Glob-top LED die
(lens)
Bond wire
Die attach
Copper 35-70-105um
Dielectric
60-100um
TIM
HS
Core aluminium
or copper
• Die is directly attached to the copper path – lesser
interfaces
• Die wire bonded to dedicated paths
• Environmentally covered with a glob top which can
contain phosphor and lens
• One to many LED chips on a board
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9
Differences in Light Engines
Chip on Board
on Ceramic PCB
Phosphor(s)
Glob-top LED die
(lens)
Bond wire
Die attach
Copper 35-70-105um
Ceramic
TIM
HS
•
•
•
•
Die is directly attached to the path – lesser interfaces
Die wire bonded to dedicated paths
No additional insulation layer
Environmentally covered with a glob top which can
contain phosphor and lens
• One to many LED chips on a board
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Differences in Light Engines
Single LED on Board
Multiple LED on Board
Single LED on PCB board
Multi LED on pcb board
HS
HS
Single LED on MCPCB board
Multi LED on MCPCB board
HS
HS
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Differences in Light Engines
Multiple Chip on Board
Multiple Chip in package
Standard FR4 brd
With via’s
HS
HS
MCPCB
Core aluminium
or copper
HS
HS
HS
HS
Ceramic/ Alum Ni
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12
Differences in Light Engines
FR4 carrier
Copper
FR4
HS
Vias 0.3-0.6,
wall thickness 25-35um,
epoxy filled, copper filled
Example:
Copper path
5mmx3mm
•
•
•
vias
0.30
0.25
0.025
0.0216
0.0491
tin filled
vias
0.30
0.25
0.025
0.0216
0.0491
copper
filled vias
0.30
0.25
0.025
0.0216
0.0491
ddrill
d finished hole
copper thickness in hole
Acopper
Ahole
mm
mm
mm
mm2
mm2
no via
0.30
0.25
0.025
0.0216
0.0491
l koper
l hole, fill
Via length
Rcopper
Rhole
Rvia
W/mK
W/mK
mm
K/W
K/W
K/W
385
0.3
0.8
96.21
54325
96.04
385
0.3
0.8
96.21
54325
96.04
385
50
0.8
96.21
326
74.28
385
385
0.8
96.21
42
29.40
Acomponent
nvia
l FR4
RFR4
Rincl. Vias
l eff
mm2
15.0
0
0.3
177.8
177.8
0.30
13.0
16
0.3
205.1
5.8
10.55
13.0
16
0.3
205.1
4.5
13.56
13.0
16
0.3
205.1
1.8
33.79
W/mK
K/W
K/W
W/mK
Carrier of standard FR4 board material 400-800-1600um
Thick copper on the top and on the bottom for spreading the heat
over a larger surface 35-70-05-140um and thicker
Add via’s to increase through-board conductivity
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13
Differences in Light Engines
FR4 carrier
LED with ceramic package
Temperature distribution
within the board
•
•
Temperature distribution
within the board & LED
Most heat is below die-thermal path
Interface to heat sink is critical because of small interface surface
area
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Differences in Light Engines
FR4 carrier
Enhanced with thermal via’s
Thermal vias
LED lamp
Top layer
Al slab (heatsink)
Fixed temperature 25C
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15
Differences in Light Engines
FR4 carrier
Enhanced with thermal via’s
SIM A-2-1
LED junction
71.3C
Thermal pad
53.8C
Top layer
Land pad
53.3C
Bottom layer
37.3C btw vias
28.8C at via
Heatsink peak
25.3C
Fixed-T
25C
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Differences in Light Engines
FR4 carrier
Enhanced with thermal via’s
SIM A-2-1
25C
28C
34C
53.2C
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Differences in Light Engines
Metal Core PCB
SIM C-1
Top layer
Cu 70mm
Prepreg
100mm
2W/mK
Al plate
1.6mm
190W/mK
Heatsink base
Al 6mm
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Differences in Light Engines
Metal Core PCB
SIM C-1
LED junction
54.8C
Thermal pad
37.4C
Top layer
Land pad
36.9C
Al plate top
27.7C
Al plate bottom
27.1C
Heatsink peak
25.1C
Fixed-T
25C
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Differences in Light Engines
Metal Core carrier
SIM C-1
LED junction
54.8C
Thermal pad
37.4C
Top layer
Land pad
36.9C
Al plate top
27.7C
Al plate bottom
27.1C
Heatsink peak
25.1C
Fixed-T
25C
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20
Differences in Light Engines
FR4 enhanced with via’s
versus Metal Core PCB
PCB 1.6mm (A)
SIM
Via pattern
PCB 0.8mm (B)
Rj-hs
Rc-hs
Rj-hs
Rc-hs
A/B-0
No vias at
all
36.15
K/W
27.5
K/W
32.45
K/W
23.8
K/W
A/B1-1
10 inner
vias
No outer
vias
23.3
K/W
14.5
K/W
20.55
K/W
11.8
K/W
A/B1-2
14 inner
vias
(staggere
d)
No outer
vias
21.85
K/W
13.1
K/W
19.15
K/W
10.4
K/W
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Differences in Light Engines
FR4 enhanced with via’s
versus Metal Core PCB
SIM
Via pattern
PCB 1.6mm (A)
PCB 0.8mm (B)
Rj-hs
Rc-hs
Rj-hs
Rc-hs
A/B2-1
10 inner
vias
72 outer
vias
22.7
K/W
13.9
K/W
20.1
K/W
11.3
K/W
A/B2-2
10 inner
vias
72 outer
vias
(12 outer
vias
smaller)
22.65
K/W
13.85
K/W
20.1
K/W
11.35
K/W
A/B2-3
10 inner
vias
132 outer
vias
22.7
K/W
13.9
K/W
20.1
K/W
11.3
K/W
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Differences in Light Engines
FR4 enhanced with via’s
versus Metal Core PCB
SIM
C-1
Metal-core No vias
pcb
Rj-hs
Rc-hs
14.9
K/W
6.2
K/W
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Difference in build up
MCPCB/ IMS
IMS with exposed copper
Copper
Dielectric
MCPCB
TIM
HS
IMS with exposed path
Copper
Dielectric
With courtesy of SinkPADTM
Copper/ AL
HS
Exposed copper/ aluminium
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Multiple LEDs on board
Effect on dissipated power
No driver on the board
Only LED heat need to be
cooled
Electrical
Power
in
Led
efficiency
HEAT
65-75%
Radiated 35-25%
Light
LEDs
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Multiple LEDs on board plus driver
Effect on dissipated power
More heat!
Also driver need
to be cooled
 Better/ larger heatsink
required
HEAT
Electrical
Power
in
10-15%
90-85%
Driver
efficiency
Electrical
Power
Led
out
efficiency
DRIVER
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HEAT
65-75%
Radiated 35-25%
Light
LEDs
26
Some notes on
Interfacing to a
heat sink
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LED Thermal resistance
From LED-junction via interface and HS to
air
Pd ≠ Pe
Rj-b’
RTI
Rspreading
Rhs-amb
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Errors in interfacing
Junction temperature for COB LEDs
•
•
For high power COB LEDs,
with ten and up LEDs, it is not
practical or always possible to
measure the junction to slug
temperature difference.
Therefore, manufactures
specify the COB’s limit by the
case temperature.
•
•
However, the case
temperature does not say
anything about the junction
temperature.
The case can be well
connected to the heat sink, but
if the area under the LED is not
connect, can lead to local hot
spot and failure of local LED.
Corresponding
‘unused’ layer
144°C
Void in applied
thermal grease
28°C
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Errors in interface selection
Coupling of COB to Heatsink
3M 3M8820
Temperatures during IR test
at 20°C ambient
100.0
90.0
Laird T-grease 1500 and screws
Temperature [°C]
80.0
70.0
60.0
50.0
40.0
Test 1 3M8820
30.0
Test 2 T1500
20.0
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Errors in interfacing
Thermal Interface Materials
Too less pressure on interface
0.8 mm FR4 with
0.15 mm TIM
1.6 mm MCPCB
with 0.15 mm TIM
Hot spots due to poor
thermal interface due to
insufficient pressure.
By applying locally additional
force to the FR4 board,
results in a decreased local
temperature.
LEDs
screws
MCPCB (Metal Core Printed Circuit Board)
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Conclusion
• Final LED junction temperature depends
– Package selection versus chip on board
– Carrier selection FR4 enanced with via, MCPCB, MCPCB
exposed path, Ceramic
– More leds with lesser individual power is thermally better
– Multichip leds and COB multichip will be thermally better
– Spreading resistance
– Interface resistance
• Interface to heat sink important, right selection of TIM
required and critical when high power LEDs are used in
combination with FR4 with vias.
• Driver on Board will add addtional power
dissipation
• Tc/Tp is only an indication of the temperature
use with care.
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Thank you
Norbert P. Engelberts
Optimal Thermal Solutions BV
[email protected]
+31 35 632 1751
+31 65 230 2258
www.ots-eu.com
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