Case Study - Field Failures - Discoloration

Case Study of LED PKG Field Failures
Discoloration
LEE SAK (Isaac,艾萨克
艾萨克)
艾萨克
Senior Engineer, Quality Team
LED Division, Semiconductor Business
SAMSUNG ELECTRONICS
Rev. 1.0
2015-12-10
* Contents
Overview
1. Ag Lead Frame Corrosion (Sulfurization
(Sulfurization))
1.1 Mechanism
1.2 Phenomena
1.3 Caused Materials in Manufacturing Site
2. Silicone Discoloration
2.1 Mechanism
2.2 Phenomena
2.3 Corrosive Chemicals
2.4 Examples of LED Degradation
2.5 Recovery Test
2.6 Chemical Compatibility Test
3. Recommendation for SSL Reliability
4. Customer Technical Service
4.1 Vf Binning test (Parallel
(Parallel--String Configuration only)
4.2 Driver Compatible test
4.3 Chemical Compatible Test
4.4 PhotometricPhotometric-Optical Test
4.5 Round–
Round–RonbinRonbin-Test
Appendix 1 SSL Configurations
----- Page 2 -----
SSL
VOCs
: Solid State Lighting
: Volatile Organic Compounds
Overview (1)
* LED PKG Field Failures
Ceramic High-power LEDs
Plastic Mid-power LEDs
Times Referenced
Ag Substrate
LFD : LeadLead-Frame Discolor , SD : Silicone discolor
----- Page 3 -----
Au substrate
Gold(Au) do not react with Corrosive Gas.
Overview (2)
* Spectrum Analysis
Intensity
Ia(λ)
-
Spectrum Analysis
Before Aging
÷
Intensity
After Aging
Spectrum Pattern
Ib(λ)
Mechanism
Silicone
Discolor
VOCs Degradation
Ag L/F
Discolor
Sulfurization
----- Page 4 -----
=
T0
f(λ)= Ia(λ)/Ib(λ)
Chip
Phosphor
Analysis Example
1 Ag Lead Frame Corrosion (sulfurization)
----- Page 5 -----
1.1 Mechanism (Sulfurization)
2Ag + H2S + ½ O2 → Ag2S + H2O
Corrosion is accelerated by
Heat and Humidity
Blackish Particle
Discolor image
----- Page 6 -----
1.2 Phenomena (Sulfurization)
CIE X,Y
Luminous Intensity
Blue Shift
Lower Lumen
----- Page 7 -----
1.3 Caused Materials in Manufacturing Site
Card Board Tray or BOX
Corrosive Particles on PET Tray
Clean PET Tray has No Problems.
Rubber Band
PSR Ink on PCB
----- Page 8 -----
2 Silicone Discoloration
Discolored as a result of exposure to incompatible Chemicals (In air-tight environment)
Good LED (Initial)
Slightly discoloration
Lm : 100%
More noticeable
Lm : 57%
Lm : 22%
URL (for reference) : http://www.youtube.com/watch?v=yuzmQtNIJGs
Sources : DELO Optoelectronic
----- Page 9 -----
Severe discoloration
Lm : 13%
2.1 Mechanism
Discolor Mechanism
*
Radical formation by heat -> Combination of Functional group (Dimerize)
-> Forming π-Bond (can absorb photon)
R
[O2]
R’
Heat & Light
Aromatic hydrocarbons
Accelerate Factor
: Heat ,
•Silicone for Encapsulant
-> Silicone Discoloration
R
R’
O
Color Change
O
Photonic Energy, Wavelength , Air movement
•PDMS (PolyDiMethylSiloxane)
----- Page 10 -----
* PMPS (PolyMethylPhenylSiloxane)
2.2 Phenomena
Caused by VOCs
Yellow Shift
Turn on (Yellowish)
Discolored as a result of exposure to incompatible chemicals
Such as Epoxy Adhesive, Conformal Coating (Parylene) ,
Solder Flux ….
----- Page 11 -----
2.3 Corrosive Chemicals
Corrosive Chemicals
Benzene
Corrosive Gases generally includes Aromatic hydrocarbons.
Cleaved aromatic side groups can react with each other and form chromophores.
----- Page 12 -----
2.4 Examples of LED Degradation _ Solder flux
* 1200mm T8 L-tube (MP PKG)
Discolored PKG
Die adhesive Silicone discolored
----- Page 13 -----
2.4 Examples of LED Degradation _ Epoxy Adhesive
* Krypton Lamp (MCP PKG)
Epoxy Adhesive
Die adhesive Silicone discolored
----- Page 14 -----
2.4 Examples of LED Degradation _ PSR
Caused by poor Thermal Design (FR4 PCB)
* 100W Street light (HP PKG)
FR4 PCB
Non Discolored
Metal PCB
Discolored
----- Page 15 -----
2.4 Examples of LED Degradation _ Current Mismatching
Bin ID
@700mA
V10
V9
V8
V7
V6
V5
V4
V3
V2
V1
V0
Voltage Range
<=
<
39.0
38.5
39.0
38.0
38.5
37.5
38.0
37.0
37.5
36.5
37.0
36.0
36.5
35.5
36.0
35.0
35.5
34.5
35.0
34.5
Module
No
Bin
#1
#2
#3
#4
#5
#6
Max
Min
Max -Min
V6
V6
V6
V6
V6
V6
37.4
37
0.4
2
3
1
Case 1 (Recommend)
Case 2 (The Worst Case)
Within One Bin Range
1 Module Mismatching
Current (mA) Temp (℃)
Current (mA)
Temp (℃)
Bin
Initial 12hr Ts (12hr)
Initial
12hr
Ts (12hr)
786
832
52.7
V6
594
485
42.7
768
766
48.3
V6
581
451
38.1
830
793
51.5
V2
1970
2486
102.3
780
792
49.6
V6
576
470
40.3
794
809
51.8
V6
592
473
40.1
888
868
55.2
V6
609
489
41.5
888
868
55.2
37.4
1970
2486
102.3
768
766
48.3
35.3
576
451
38.1
120.0 102.0
6.9
2.1 1394.0 2035.0
64.2
4
5
6
Parallel Configuration
See Appendix 1 SSL Configuration
----- Page 16 -----
Bin
V6
V6
V2
V6
V6
V2
37.4
35.3
33.9
Case 3 (The Worse Case)
2 Module Mismatching
Current (mA)
Temp (℃)
Initial
12hr
Ts (12hr)
607
412
38.5
576
400
38.5
1327
1730
75.3
571
390
36.4
570
400
38.3
1270
1530
71.5
1327
1730
75.3
570
390
36.4
757.0 1340.0
38.9
* 200W Street light (HP PKG)
2.5 Recovery Test _ Procedure
Purpose :
To verify whether this failure is caused by LED itself or External Gases (VOCs)
Test Set up
(On 12 Series Demo Board)
1) Bias Setting (750mA)
2) Turn on (Aging Start )
※ Test Condition : open-air environment (Ta : 25℃
℃±2℃
℃)
----- Page 17 -----
2.5 Recovery Test _ Result
Initial
Recovery Test
After 60hrs
#1
#2
#3
* Examples showing the reversibility of VOCs discoloration
----- Page 18 -----
After 168hrs
Luminous Flux
2.6 Chemical Compatibility Test (Example)
1. Test Kit with sixteen LEDs
2. Make an airtight environment
with glass vials
3. On Testing
Lasts for 6weeks (1008 hrs)
Test Kits include Driver, MCPCB, Glass vials, Mixing Cup and SMT Materials.
----- Page 19 -----
2.6 Chemical Compatibility Test
*
Recommend Test Condition (LH351B)
- Ts range
- Current
- Duration
: 75℃ ~ 85℃ (@Ta 25℃)
: 700mA ~ 1050mA Constant Current Mode
: 6 weeks (1008 hrs)
Gen 1
Gen 2
----- Page 20 -----
3 Recommendation for SSL Reliability
* Adhesive & TIM
Chemical
Usage Image
Commercial Product
Dow Corning SE-9185
Dow Corning SE-9186
2nd Optic
Adhesive
Henkel Loctite 3280
Dow Corning TC-4025
Dow Corning TC-5080
Thermal Interface
Material
Dow Corning TC-5121
ESD社
FTP15
This Recommend is provided for informational purpose only and is not a warranty or a specification.
----- Page 21 -----
3 Recommendation for SSL Reliability
* Solder Flux
Solder Model (SenJu 社)
M705-GRN360-KV (SenJu 社)
Alloy Composition
Sn 96.5%, Ag 3.0%, Cu 0.5%
Melting temperature
217 - 219°C
Powder Size
25 – 36um
Flux Content
11.50%
Sources : http://www.senju.com/images/pdf/M705
http://www.senju.com/images/pdf/M705--GRN360GRN360-KV%20Series%20fly.pdf
This Recommend is provided for informational purpose only and is not a warranty or a specification.
----- Page 22 -----
3 Recommendation for SSL Reliability
* PSR
* Recommended White Solder Resist Ink
1) LEW7S (Taiyo ink mfg.co.ltd. )
This Recommend is provided for informational purpose only and is not a warranty or a specification.
----- Page 23 -----
4. Core Customer Technical Services (Examples)
----- Page 24 -----
4.1 Vf Binning Test
All 6 Module / In one Bin Range
1(V6)
2(V6)
3(V6)
Current (mA
(mA)
mA) / 12hr Aging
4(V6)
Module
No
5(V6)
6(V6)
#1
#2
#3
#4
#5
#6
Max
Min
Max -Min
Case 1 (Recommend)
Within One Bin Range
Current (mA) Temp (℃)
Bin
Initial 12hr Ts (12hr)
V6
786
832
52.7
V6
768
766
48.3
V6
830
793
51.5
V6
780
792
49.6
V6
794
809
51.8
V6
888
868
55.2
37.4
888
868
55.2
37
768
766
48.3
0.4
120.0 102.0
6.9
Temp. ℃ / 12 hr Aging
----- Page 25 -----
4.2 Driver Compatible Test (1)
Input
Voltage
fin
Iin
Pin
I_inrush
[Hz]
[mA]
mA]
[W]
[A]
140
50
141.4
19.8
230
50
85.2
19.6
270
50
75.6
19.6
3.35
I_THD
Vout
Iout
Efficiency
Ripple
[%]
[V]
[mA]
mA]
[%]
[mA]
mA]
0.99
4.79
23.9
702
84.7%
660
0.98
4.79
23.9
705
86.0%
655
0.96
7.14
23.9
709
86.5%
650
Power Factor
CH2 : 3.35A : I_inrush
----- Page 26 -----
4.2 Driver Compatible Test (2)
-20℃
30℃
60℃
140V
50Hz
Imax : 968mA (ch1)
Imax : 1.048A (ch1)
Imax : 1.04A (ch1)
230V
50Hz
Imax : 1.04A (ch1)
Imax : 1.064A (ch1)
Imax : 1.128A (ch1)
270V
50Hz
Imax : 1.064A (ch1)
Imax : 1.088A (ch1)
----- Page 27 -----
Imax : 1.08A (ch1)
4.3 Chemical Compatible Test
* Test Conditions/Duration (Gen 1)
- Ts 75℃ (@Ta 25℃) , 700mA) - 6 weeks (1008 hrs)
* Test Conditions/Duration (Gen 2)
- Ts 75℃ (@Ta 25℃) , 860mA)
- 6 weeks (1008 hrs)
----- Page 28 -----
4.4 Photometric-Optical Test (1)
Input V
Input I
Input Power
PF
Lumen/ Watt
Luminous Flux
Luminous intensity
Unit
V
A
W
lm/ W
Lm
Cd
140V
139.7
0.146
20.27
0.993
91.4
1852.4
1080.5
230V
229.8
0.089
20.07
0.981
92.8
1862.7
1088.5
270V
269.8
0.078
20.27
0.966
92.5
1874.2
1093.4
Lumination (@1
(@1m)
Lx
613.4
616.5
620.3
beamAngle
°
60.3~ 139.7(90.9)
60.3~ 139.7(90.9)
60.3~ 139.7(90.9)
CCT
K
X
Y
-
5735
0.3272
0.3391
76.8
0.0014
5742
0.3271
0.339
76.7
0.0014
5740
0.3272
0.3389
76.6
0.0013
CIE X,Y
CRI
Duv
140V/ 50Hz
230V/50Hz
----- Page 29 -----
270V/50Hz
4.4 Photometric-Optical Test (2)
Ts point
w/o Cover Glass (Ts : 41.8℃)
With Cover Glass (Ts : 46.2℃)
140V/ 50Hz
230V/50Hz
270V/50Hz
----- Page 30 -----
4.5 Round – Robin – Test
Site
Samsung
Spectroradiometer
社
CAS140CT
(IS
Germany)
社
社
HASS2000
China/SEA
(Everfine
Customers
KRISS
(APMP)
NIST
(APMP)
NIM
(APMP)
China)
社
China)
CAS140CT
(IS
社
Germany)
CAS140CT
(IS
Germany)
社
HASS2000
(Everfine
Array
Array
Test method
IS Configuration
Pulse mode
2π
(IP Count Base / Tj 25)
(25cm)
Pulse mode
2π
(Auto Setting)
(30cm)
Setting Fix
2π
(10s ~ 1min)
(30cm)
Dut Type
Comment
PKG
KRISS Traceability
PKG
NIM Traceability
PMS50/80
(Everfine
Type
China)
Scanning
Array
Array
Array
Pulse mode
4π
(IP Count Base / Tj 25)
(30cm)
Ts 25도
(After 5minit
4π
Aging)
(1.5m)
Pulse mode
2π
(Auto Setting)
(30cm)
NMI : National Metrology Institute
APMP : Asia Pacific Metrology Program
• Key NMI
PTB : Germany
NPL : UK
NPLI : India (NPL of India)
LNE : France
NIST : USA
KRISS : Korea
NIM : China
----- Page 31 -----
PKG
PKG
PCB only
PKG
Korea NMI
USA NMI
China NMI
Appendix 1 SSL Configuration (1)
* Integral Platform
Modular Platform
Integral Platform
: Model by Model
Series Configuration
: 36 Series ,52 Series, 78 Series
Parallel Strings Configuration : 15S8P , 12S10P
Matrix Configuration )
: 10S3P , 11S4P
Modular Platform : For Mass Customization
Series Configuration
: 54Series (18*3) , 72 Series (18* 4)
Multi-Channel
: 18 Series * 3P~7P
Parallel String Configuration
: 14 Series * 3P~6P , 18 Series * 3P ~ 4P
----- Page 32 -----
Appendix 1 SSL Configuration (2)
All PKG exactly the Same Current.
Advantage : The implementation is very simple with only a single circuit.
There are no current imbalance issues as all LEDs receive identical Current.
System Efficiencies tend to be high as it is easier to optimize efficiency with high
voltage and low current.
Disadvantage : Output voltage can become very high which may translate into a safety issue.
A open LED PKG can Cause the entire lamp to cease operation.
Failure Modes : If a single LED fails short, There is virtually no impact on the other LEDs.
If single LED fails Open then the current path is broken, all LEDs are turned off.
----- Page 33 -----
Appendix 1 SSL Configuration (3)
Current is divided between the Various Strings
based on how well each of the strings are
matched.
Advantage
: Requires the use of only a single Driver and output voltage can be kept rather low.
(Can be meet SELV- equivalent)
By Vf Binning in Modular Design, reasonable Current sharing can be achieved
among the paralleled LED Stings.
Disadvantage : 1. Vf Binning is impossible in Integral Design, So small differences in the Vf of the various LEDs
can cause significant imbalances in current.
2. The improved accuracy of current sharing is achieved at the external Resistors,
But in this case, increased power dissipation in the resistors.
3. Any Failure of an LED Open or Short circuit can Cause significant stress on the remaining LEDs.
Failure Modes : If a single LED Fails short, the string in which the failed LED resides will take significantly
greater than its shared of the current. The stress on the LEDs in this string will increase
significantly thus increasing the likelihood that a second LED will Fail.
----- Page 34 -----
Appendix 1 SSL Configuration (4)
The most Risk
Configuration
Advantage
: If one LED fails, The remaining LEDs still Operate.
Disadvantage : In the worst case the current distribution can be very unsymmetrical.
Non-Uniform current sharing leads to non-uniform light and Thermal distribution in the SSL.
----- Page 35 -----
Appendix 1 SSL Configuration (5)
The most Robust Configuration
Advantage
: High Accuracy of current regulation can be achieved with minimum string voltage to ease
safety considerations.
Failures in any one string Do not affect the other strings.
Disadvantage : The Cost of the Driver is Increased somewhat although not nearly as much as
four independent Drivers.
Failure Modes : If any LED Fails short, the other LEDs in that string continue to operate while the other strings
operate normally.
----- Page 36 -----
Revision History
Revision
Data
Rev. 1.0 2015-12-10
Page
-
Description
First Edition
If you have any further questions , please contact :
LEE SAK (Isaac, 艾萨克)
艾萨克
Office : (82)-(70)-7142-1388 , [email protected]
Mobile : (82)-(10)-9177-1225 , [email protected]
----- Page 37 -----
Writer
LEE SAK
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