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Low Voiding Reliable Solder Interconnects for LED Packages on Metal Core PCBs (English)
 

Low Voiding Reliable Solder Interconnects for LED Packages on Metal Core PCBs (English)

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Alpha®, the world leader in the production of electronic soldering materials, recently presented a paper on Low Voiding Reliable Solder Interconnects for LED Packages on Metal Core PCBs. The paper ...

Alpha®, the world leader in the production of electronic soldering materials, recently presented a paper on Low Voiding Reliable Solder Interconnects for LED Packages on Metal Core PCBs. The paper was presented by Andy Yuen, Technical Services Director of Alpha Southern China, at this year’s SMTA China Conference in Shenzhen. The presentation received the award of “The Best Paper of Technology Conference Three SMTA South China 2012” on August 29, 2012.

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    Low Voiding Reliable Solder Interconnects for LED Packages on Metal Core PCBs (English) Low Voiding Reliable Solder Interconnects for LED Packages on Metal Core PCBs (English) Presentation Transcript

    • Low Voiding ReliableSolder Interconnects forLED Packages on Metal Core PCBs
    • Outline/Agenda • Introduction • Assembly • Components • Materials • Process • Results of Experiments • Conclusions •Q&APRIVILEGED AND CONFIDENTIAL MATERIALS
    • Introduction – LED Packages • Lumen maintenance requirement for LED packages used in commercial & outdoor residential lighting is 70% lumen maintenance for 50% of population after 35,000 hours and 3 year warranty (Energy Star A; IESNA LM-80) • Good thermal management is key to long term stability of light output (brightness) and color temperature of LED lights – Solder joints with low voiding for low thermal resistancePRIVILEGED AND CONFIDENTIAL MATERIALS
    • Package Assembly • For this study used commercially available LED package, metal core boards and solder pastes – Luxeon Rebel LED – Metal Core PCB substrate w/ Aluminum core, Copper circuitry and 2 dielectric types – 4 solder pastes – Pb-free; no clean; zero halogen; 4 alloy typesPRIVILEGED AND CONFIDENTIAL MATERIALS
    • LED Package • Surface mount package w/ ceramic substrate & metal interconnect • Solderable to next level substrate - bottom side with thermal pad under LED, and (2) pads for electrical connections • Hard silicone lens over LEDPRIVILEGED AND CONFIDENTIAL MATERIALS
    • Metal Core PCB (MCPCB)• Aluminum core; Copper circuitry and (2) Dielectric types – Dielectric A: High thermal conductivity for good conduction of heat into metal core – Dielectric B: Low modulus for reducing solder joint strain, especially for assemblies w/ large CTE mismatch between package and boardPRIVILEGED AND CONFIDENTIAL MATERIALS
    • Solder Pastes • All with Type 3 lead-free solder powder; no-clean; zero halogen ID Alloy Attribute A SAC305 Broad application range B Maxrel Superior creep resistance, temp cycling / vibration performance C SACX Plus Reduced Ag for lower cost 0807 D SnBiAg Low melting point (<140 C)PRIVILEGED AND CONFIDENTIAL MATERIALS
    • Assembly Process & Testing • Assembled 36 LEDs per board; (5) boards per solder paste and dielectric type • Standard SMT equipment – printing, P/P, reflow • Solder paste printing: 5 mil stencil, on-contact printing at 2.54 cm/sec; 268 gr/cm pressure; 0.051 cm/sec stencil release • Reflow in air with high soak profiles • % Voids by Xray; 50% solder joints per board measuredPRIVILEGED AND CONFIDENTIAL MATERIALS
    • Reflow Profile Test • Pre-screening test with high soak & straight ramp profiles, SAC305 paste & Type B dielectric MCPCB board Boxplot of % Voids - MCPCB with Type B Dielectric; SAC305 Paste 25 20 15 % Voids 10 5.71 5.87 5 0 High Soak Str Ramp ProfilePRIVILEGED AND CONFIDENTIAL MATERIALS
    • Reflow Profile – SAC & Maxrel Alloy Pastes 150-200°C, 115 sec soak; 240°C peak; 67 sec TALPRIVILEGED AND CONFIDENTIAL MATERIALS
    • Reflow Profile – SnBiAg Alloy Paste 100-110°C, 75 sec soak; 175°C peak; 60 sec TALPRIVILEGED AND CONFIDENTIAL MATERIALS
    • Test ResultsPRIVILEGED AND CONFIDENTIAL MATERIALS
    • Main Effects Plot for Dielectric & Paste Alloy Main Effects Plot for % Voids Data Means Board Dielectric Paste Alloy 20.0 17.5 15.0 Mean 12.5 10.0 7.5 5.0 A B Maxrel SAC305 SACX0807 SnBiAgPRIVILEGED AND CONFIDENTIAL MATERIALS
    • % Voids vs Board Dielectric Boxplot of % Voids 35 30 25 20 % Voids 15 10.465 10.805 10 5 0 A B Board DielectricPRIVILEGED AND CONFIDENTIAL MATERIALS
    • % Voids vs Paste Alloy & Dielectric Boxplot of % Voids 35 30 25 20 20 % Voids 15 10 5 0 Board Dielectric A B A B A B A B Paste Alloy Maxrel SAC305 SACX0807 SnBiAgPRIVILEGED AND CONFIDENTIAL MATERIALS
    • Void Sizes LED Assembly Voids Sizes 100% B Diel/ SAC305 90% A Diel/ SAC305 A Diel/ SnBiAg 80% B Diel/ SnBiAg A Diel/ Maxrel 70% B Diel/ Maxrel A Diel/ SACX0807 % of Joints 60% B Diel/ SACX0807 50% 40% 30% 20% 10% 0% ZERO 0-4% 4-8% 8-12% 12-16% 16-20% >20% Void Size as % of Joint AreaPRIVILEGED AND CONFIDENTIAL MATERIALS
    • Average Void Sizes LED Assembly Average Void Size 0.7 Dielectric A Averge Void Size (% joint area) 0.6 Dielectric B 0.5 0.4 0.3 0.2 0.1 0 SAC305 Maxrel SACX0807 SnBiAg Paste AlloyPRIVILEGED AND CONFIDENTIAL MATERIALS
    • Maximum Void Sizes LED Assembly Max. Void Size 30.0 Dielectric A Max. Void Size (% joint area) 25.0 Dielectric B 20.0 15.0 10.0 5.0 0.0 SAC305 Maxrel SACX0807 SnBiAg Paste AlloyPRIVILEGED AND CONFIDENTIAL MATERIALS
    • Typical Xray Voids Images Paste Alloy/ SAC305 Maxrel SACX SnBiAg Dielectric Type 0807 MCPCB Dielectric A %Voids 9.3 15.8 10.0 11.6 MCPCB Dielectric B % Voids 7.2 12.6 12.3 12.3PRIVILEGED AND CONFIDENTIAL MATERIALS
    • Summary/Conclusions • (4) different metal alloy solder pastes were evaluated for % voids in the reflowed joints formed between a LED surface mount package and MCPCB substrates having (2) different dielectric types • Overall, the board dielectric type had little effect on the solder joint % voids, whereas the solder alloy had a more significant effect • The Type A dielectric boards resulted the lowest average and maximum void sizes, for all pastes, and the SnBiAg paste resulted in the smallest void sizes • Overall, >90% of the solder joints had void sizes ≤4% of the solder joint area and less than 20% voids on average • The SAC305 alloy paste combined with the Type B board dielectric resulted in the lowest % voids (<8.5%) • The boards from this study will be subjected to further tests including electrical/optical, die shear, thermal cycling/shock, and solder joint characterization by cross-sectioningPRIVILEGED AND CONFIDENTIAL MATERIALS
    • For More Information Please Contact: Ravi Bhatkal – VP, Energy Technologies Rbhatkal@cookson.com +1-908-791-3013 Amit Patel – Technology Analyst Apatel@cookson.com +1-908-791-3051PRIVILEGED AND CONFIDENTIAL MATERIALS