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