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Ensuring and predicting the reliability of cpv
- 1. Ensuring and Predicting the Reliability of Concentrated Photovoltaics (CPV): Interconnect Structures © 2004 - 2009 Greg Caswell and Craig Hillman DfR Solutions February 15, 2010 Jordan Ross Indium Corporation
- 2. Reliability Challenges in CPV Interconnects Current material selection for CPV interconnects are insufficient Filled epoxy is cheap ‘temporary’ solution Poor thermal conductivity prevents migration to higher concentration levels, greater efficiencies Insufficient reliability to meet 25-year lifetime Extensive life requirements, short product development cycle demands ‘proof-of-concept’ before hardware build Waiting till test to validate reliability requirements is high risk proposition Requires reliability prediction of interconnect structures in the concept and design stages New materials by Indium Corporation and new reliability algorithms by DfR Solutions provide direct solutions to these industry-limiting issues © 2004 - 2007 Inappropriate above 1000 Suns 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474-0607 Fax (240) 757-0053 2009 www.DfRSolutions.com 2
- 3. Typical CPV Receiver - Material Stack-Up Material Comments Fresnel Lens, Cassegrain Mirror Parabolic Mirror III- IV, 10 x 10 x 0.2 mm Metalized Backside E / T Conductive Die Attach Epoxy 24x24 x0.38mm: Alumina, BEO, ALN Cu Ni Au Both Sides Non Conductive Adhesive Heat Spreader Non Conductive Adhesive © 2004 - 2007 Concentrated SUN 200 to 1000+ Receiver Module Triple Junction PV Die TIM 0 Ceramic TIM 1 Cu / Al: Heat Sink / Rail TIM 2 Aluminum Heat Sink (Back Panel / Rail) Design Comments 200 to 1000+ Suns Tj,max 100C to Meet 25 Year Life and Efficiency Better Thermal Conductivity Can Improve Efficiency Good CTE Match to Die OK Thermal Conductivity Electrical Insulator – High Pot Test Absorb CTE Mismatch Al2O3 / Cu or Al Good Thermal Conductor Thermal Path to Baseplate 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474-0607 Fax (240) 757-0053 2009 www.DfRSolutions.com 3
- 4. Typical CPV Receiver - Thermal View Thermal Conductivity ( W / mK ) 4.0 / 7.0 1 .0 / 4.0 210 / 360 1 .0 / 4.0 © 2004 - 2007 Concentrated SUN 200 to 1000+ Receiver Module Triple Junction PV Die TIM 0 Ceramic TIM 1 Cu / Al: Heat Sink / Rail TIM 2 Aluminum Heat Sink (Back Panel / Rail) TC -40C to 110C 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474-0607 Fax (240) 757-0053 50 / 60 46 CTE ( ppm / C) 5.0 / 6.0 5.5 16 / 24 2009 www.DfRSolutions.com 4
- 5. CPV Cell Performance NanoBond vs. Adhesive Delta Tj,max Increase vs. Suns •Lower Tj,max - Increase Lifetime •Or More Sun Headroom © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474-0607 Fax (240) 757-0053 Adhesive NanoBond® DNI 850 W/m2 Efficiency 35% Base Plate Held 28C 2009 www.DfRSolutions.com 5 5 1 Sun = 85 mW/mm2 x 500 = 425 mW/mm2 Die Surface Area = 100mm2 Power Incident Die Surface = 42.5W Conversion Efficiency = 35% Pdc = 14.9 W Pdiss = 27.6 W – Thermal Management Tj,max Conversion Efficiency ~ 0.5% / 10°C Maintain 100°C to Meet 25 Year Life Time Sun Concentration Levels Typically ~ 500 X (Suns) CPV Roadmaps – X will Continue to Increase
- 6. NanoBond® Soldering Approach – A foil with thousands of nanoscale layers of aluminum – Heat generated by intermixing of aluminum and nickel – Foil acts as a controllable, rapid, local heat source. – Heat of mixing melts the adjoining solder layers. – Melted layers lead to formation of metallic bond © 2004 - 2007 and nickel. 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474-0607 Fax (240) 757-0053 layers. 2009 www.DfRSolutions.com 6
- 7. Tin Surface Finish • Bottom of CPV Module •Top of Heat Spreader • Conventional Reflow Not Required Cu vs. Al Heat Spreader • Cu is Better TCE Match to Receiver Module • Also Better Thermal Conductor © 2004 - 2007 NanoBond® Configuration for CPV Receiver Modules PV Die CPV Receiver Substrate 80um NanoFoil® Heat Spreader NanoFoil® Replaces TIM1 Adhesive • Lower Tjmax • Increased Efficiency • Improved Lifetime 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474-0607 Fax (240) 757-0053 Tin Surface Finish 2009 www.DfRSolutions.com 7
- 8. Solder vs. Adhesive Thermal FEA Model – 30W Heat Flow © 2004 - 2007 Tjmax= 38C BLT=250um K=25 W/Km • Tjmax= 46C • BLT=50um • K=1W/Km 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474-0607 Fax (240) 757-0053 2009 www.DfRSolutions.com 8 8
- 9. © 2004 - 2007 NanoBond® Solder Solution Pressure Heat Sink Solder NanoBond® Solder Bond Post 1000 Cycles Cu Heat Sink and Receiver Module 1000 cycles completed, no degradation -25 to +125C (8.5C per minute ramp) 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474-0607 Fax (240) 757-0053 2009 www.DfRSolutions.com 9 9
- 10. Original Bond After 540 cycles After 940 cycles *Thermal Resist. (Kmm2/W) *Thermal Resist. (Kmm2/W) *Thermal Cond. (W/Km) Bondline Thickness (μm) Bonding Method NanoBond 447 42.2 10.6 10.9 Screen printed DBC NanoBond 467 30.7 14.4 14.6 Spray coated DBC *Thermal Cond. (W/Km) 42.3 32.4 *Thermal Cond. (W/Km) 41.0 32.0 *Thermal Resist. (Kmm2/W) 10.6 15.2 Epoxy1 50 0.85 58.96 0.81 61.9 0.76 65.86 (3M) Epoxy 2 50 2.83 17.6 (Epo-Tek) •Bond size 24 mm x 24 mm •DBC material properties have been corrected using laser flash •Copper thickness 1.6 mm © 2004 - 2007 Laser Flash Analysis Results Bonds started - -- - falling apart at 400 cycles 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474-0607 Fax (240) 757-0053 2009 www.DfRSolutions.com 10
- 11. Information Property of Indium Corp. Engineered Solder Materials: ESM Heat-Spring®: What is it? • Material Description – Made from Indium or Indium Tin as standard alloys – Custom Alloys available – We alter the surface so contact resistance is reduced – We use high conductive metal 86w/mk – We custom package for your application – We standard pack in Tape and Reel – We can recycle it and reclaim it – We can offer you a credit on un-used material – It’s a “green” TIM
- 12. Information Property of Indium Corp. Engineered Solder Materials: ESM Soft Metal TIM Attributes • High thermal conductivity 86W/mK – Low bulk resistance— insensitive to BLT – Heat spreading • Conformability – Plastic deformation provides low contact resistance path, especially after time zero (burn-in period) – Inherent gap filling for co-planarity issues: – HSD: +/- .003” – HSG: +/- .010” – Complies with CTE mismatch • Stability/ Advantages – No out-gassing – No bake-out or pump-out – Easy to handle – Reclaimable/ recyclable • Thickness – HSD pattern, minimum thickness before Patented Heat-Spring Process is 75um, after the HSD process thickness will increase 75um. – HSG pattern, minimum thickness before Patented Heat-Spring process is 150um, after HSG is 300um – HSG pattern can be applied to a 250um preform and after HSG process will be 500um thick. – Max Thickness is well over .25 inches if necessary.
- 13. Information Property of Indium Corp. Engineered Solder Materials: ESM Stack-up Pictorial TIM1: Indium Solder Preforms, or conceptual Liquid Metal. TIM1.5: Heat-Spring®, Liquid Metal TIM2: Heat-Spring®, Liquid Metal Burn-in and Test: Heat-Spring® and Aluminum Indium Clad preforms.
- 14. Interconnect Reliability Prediction DfR has extensive experience in developing material degradation algorithms for electronics applications These models have been adapted to assess cycles to failure for Concentrated Photovoltaic (CPV) modules Typical CPV architecture 25 mm square CPV receiver DBC on alumina Heatsinks are copper and aluminum Solder is SAC305 © 2004 - 2007 Overview Model Inputs Environment Max temperature Min temperature Dwell times Direct Bond Copper (DBC) Architecture Thicknesses Interconnect Material Composition (SAC305, etc.) Material Properties Heatsink Material Composition (Cu, Al, etc.) Material Properties 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474-0607 Fax (240) 757-0053 2009 www.DfRSolutions.com 14
- 15. Reliability Prediction: Results 1000000 100000 10000 1000 Time to Failure (400um SAC305 Bondline Thickness) 1000000 100000 10000 1000 Time to Failure (250um SAC305 Bondline Thickness) Clearly demonstrates influence of minimum temperature (mountain vs. desert), change in temperature, and bondline thickness Allows for tradeoff analysis and rapid assessment of existing interconnect materials and architecture © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474-0607 Fax (240) 757-0053 2009 www.DfRSolutions.com 15 100 0 20 40 60 80 100 120 140 160 180 Change in Temperature (oC) Time to Crack Initiation (Cycles) Minimum Temperature - 40C - 25C 0C 25C 100 0 20 40 60 80 100 120 140 160 180 Change in Temperature (oC) Time to Crack Initiation (Cycles) Minimum Temperature - 40C - 25C 0C 25C
- 16. Summary DfR and Indium provide a turn-key solution for the reliability assurance of CPV modules New materials and technology for radical improvement in interconnect robustness Commercially available NanoBonding and Heat Spring Interconnect reliability algorithm adapted to assess cycles to failure for Concentrated Photovoltaic (CPV) modules © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474-0607 Fax (240) 757-0053 2009 www.DfRSolutions.com 16