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Low Voiding Reliable
Solder Interconnects for
LED Packages on Metal
Core PCBs
PRIVILEGED AND CONFIDENTIAL MATERIALS
Outline/Agenda
• Introduction
• Assembly
• Components
• Materials
• Process
• Result...
PRIVILEGED AND CONFIDENTIAL MATERIALS
Introduction – LED Packages
• Lumen maintenance requirement for LED
packages used in...
PRIVILEGED AND CONFIDENTIAL MATERIALS
Package Assembly
• For this study used commercially available LED
package, metal cor...
PRIVILEGED AND CONFIDENTIAL MATERIALS
LED Package
• Surface mount package w/ ceramic substrate &
metal interconnect
• Sold...
PRIVILEGED AND CONFIDENTIAL MATERIALS
Metal Core PCB (MCPCB)
• Aluminum core; Copper
circuitry and (2) Dielectric
types
– ...
PRIVILEGED AND CONFIDENTIAL MATERIALS
Solder Pastes
• All with Type 3 lead-free solder powder; no-clean; zero
halogen
ID A...
PRIVILEGED AND CONFIDENTIAL MATERIALS
Assembly Process & Testing
• Assembled 36 LEDs per board; (5) boards per
solder past...
PRIVILEGED AND CONFIDENTIAL MATERIALS
Reflow Profile Test
• Pre-screening test with high soak & straight ramp
profiles, SA...
PRIVILEGED AND CONFIDENTIAL MATERIALS
Reflow Profile – SAC & Maxrel Alloy Pastes
150-200°C, 115 sec soak; 240°C peak; 67 s...
PRIVILEGED AND CONFIDENTIAL MATERIALS
Reflow Profile – SnBiAg Alloy Paste
100-110°C, 75 sec soak; 175°C peak; 60 sec TAL
PRIVILEGED AND CONFIDENTIAL MATERIALS
Test Results
PRIVILEGED AND CONFIDENTIAL MATERIALS
Main Effects Plot for Dielectric & Paste Alloy
BA
20.0
17.5
15.0
12.5
10.0
7.5
5.0
S...
PRIVILEGED AND CONFIDENTIAL MATERIALS
% Voids vs Board Dielectric
BA
35
30
25
20
15
10
5
0
Board Dielectric
%Voids
10.8051...
PRIVILEGED AND CONFIDENTIAL MATERIALS
% Voids vs Paste Alloy & Dielectric
Paste Alloy
Board Dielectric
SnBiAgSACX0807SAC30...
PRIVILEGED AND CONFIDENTIAL MATERIALS
Void Sizes
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
%ofJoints
ZERO 0-4% 4-8% 8-12...
PRIVILEGED AND CONFIDENTIAL MATERIALS
Average Void Sizes
LED Assembly Average Void Size
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
SAC3...
PRIVILEGED AND CONFIDENTIAL MATERIALS
Maximum Void Sizes
LED Assembly Max. Void Size
0.0
5.0
10.0
15.0
20.0
25.0
30.0
SAC3...
PRIVILEGED AND CONFIDENTIAL MATERIALS
Typical Xray Voids Images
Paste Alloy/
Dielectric Type
SAC305 Maxrel SACX
0807
SnBiA...
PRIVILEGED AND CONFIDENTIAL MATERIALS
Summary/Conclusions
• (4) different metal alloy solder pastes were evaluated for % v...
PRIVILEGED AND CONFIDENTIAL MATERIALS
For More Information Please Contact:
Ravi Bhatkal – VP, Energy Technologies
Rbhatkal...
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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 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.

Published in: Technology
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Low Voiding Reliable Solder Interconnects for LED Packages on Metal Core PCBs (English)

  1. 1. Low Voiding Reliable Solder Interconnects for LED Packages on Metal Core PCBs
  2. 2. PRIVILEGED AND CONFIDENTIAL MATERIALS Outline/Agenda • Introduction • Assembly • Components • Materials • Process • Results of Experiments • Conclusions • Q & A
  3. 3. PRIVILEGED 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 resistance
  4. 4. PRIVILEGED 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 types
  5. 5. PRIVILEGED 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 LED
  6. 6. PRIVILEGED 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 board
  7. 7. PRIVILEGED 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 0807 Reduced Ag for lower cost D SnBiAg Low melting point (<140°C)
  8. 8. 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 measured
  9. 9. PRIVILEGED AND CONFIDENTIAL MATERIALS Reflow Profile Test • Pre-screening test with high soak & straight ramp profiles, SAC305 paste & Type B dielectric MCPCB board Str RampHigh Soak 25 20 15 10 5 0 Profile %Voids 5.875.71 Boxplot of % Voids - MCPCB with Type B Dielectric; SAC305 Paste
  10. 10. PRIVILEGED AND CONFIDENTIAL MATERIALS Reflow Profile – SAC & Maxrel Alloy Pastes 150-200°C, 115 sec soak; 240°C peak; 67 sec TAL
  11. 11. PRIVILEGED AND CONFIDENTIAL MATERIALS Reflow Profile – SnBiAg Alloy Paste 100-110°C, 75 sec soak; 175°C peak; 60 sec TAL
  12. 12. PRIVILEGED AND CONFIDENTIAL MATERIALS Test Results
  13. 13. PRIVILEGED AND CONFIDENTIAL MATERIALS Main Effects Plot for Dielectric & Paste Alloy BA 20.0 17.5 15.0 12.5 10.0 7.5 5.0 SnBiAgSACX0807SAC305Maxrel Board Dielectric Mean Paste Alloy Main Effects Plot for % Voids Data Means
  14. 14. PRIVILEGED AND CONFIDENTIAL MATERIALS % Voids vs Board Dielectric BA 35 30 25 20 15 10 5 0 Board Dielectric %Voids 10.80510.465 Boxplot of % Voids
  15. 15. PRIVILEGED AND CONFIDENTIAL MATERIALS % Voids vs Paste Alloy & Dielectric Paste Alloy Board Dielectric SnBiAgSACX0807SAC305Maxrel BABABABA 35 30 25 20 15 10 5 0 %Voids 20 Boxplot of % Voids
  16. 16. PRIVILEGED AND CONFIDENTIAL MATERIALS Void Sizes 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% %ofJoints ZERO 0-4% 4-8% 8-12% 12-16% 16-20% >20% Void Size as % of Joint Area LED Assembly Voids Sizes B Diel/ SAC305 A Diel/ SAC305 A Diel/ SnBiAg B Diel/ SnBiAg A Diel/ Maxrel B Diel/ Maxrel A Diel/ SACX0807 B Diel/ SACX0807
  17. 17. PRIVILEGED AND CONFIDENTIAL MATERIALS Average Void Sizes LED Assembly Average Void Size 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 SAC305 Maxrel SACX0807 SnBiAg Paste Alloy AvergeVoidSize(%jointarea) Dielectric A Dielectric B
  18. 18. PRIVILEGED AND CONFIDENTIAL MATERIALS Maximum Void Sizes LED Assembly Max. Void Size 0.0 5.0 10.0 15.0 20.0 25.0 30.0 SAC305 Maxrel SACX0807 SnBiAg Paste Alloy Max.VoidSize(%jointarea) Dielectric A Dielectric B
  19. 19. PRIVILEGED AND CONFIDENTIAL MATERIALS Typical Xray Voids Images Paste Alloy/ Dielectric Type SAC305 Maxrel SACX 0807 SnBiAg MCPCB Dielectric A %Voids 9.3 15.8 10.0 11.6 MCPCB Dielectric B % Voids 7.2 12.6 12.3 12.3
  20. 20. PRIVILEGED 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-sectioning
  21. 21. PRIVILEGED 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 +1-908-791-3051

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