September 14, 2011

1. Ultrasonic Soldering for Joining Dissimilar Materials September 14, 2011 Kirk Cooper Senior Engineer, Materials Email: kcooper@ewi.org Phone: 614.688.5069

2. What’s so exciting about soldering?

3. This is!

4. Outline • What is ultrasonic soldering and how does it work? • What’s the advantage of using ultrasonic soldering? • What is EWI SonicSolder™? • What can I join using ultrasonic soldering? • What are some examples of ultrasonic soldering between dissimilar materials?

5. Ultrasonic Soldering • Ultrasound energy (20 kHz and up typical) generates cavitation • Cavitation erodes surface oxide, lowering surface energy thereby enabling wetting by the molten solder • Bonding occurs by: • Van der Waal’s forces: electrostatic attraction • Metallic bond: electron sharing • Filler metal melts below 450°C

6. Ultrasonic Solder Pots • Transducers are attached to heated pot or immersed at the surface • Parts are pretinned by dipping Two different pot designs

7. Ultrasonic Soldering Irons Misonix • Much like a conventional iron except the tip can be ultrasonically energized • Operating frequency 20-60 kHz • Typical power levels <30 W • Production equipment can be designed and constructed from commercial components 30-kHz soldering iron Bellex Int. 60-kHz soldering iron

8. Custom Soldering Iron EWI-designed large-scale ultrasonic soldering iron with 1-in.-wide horn Power levels up to 300 W

9. EWI Expertise….Scale-Up EWI has developed larger tools to increase process speed Larger sonotrode designs require more ultrasonic power, but are required to increase pass width Sonotrode Scale-Up: 1- to 4-in. wide, 1200-W ultrasonic power

10. Electrically heated iron tip Hot Plate Ultrasonic pretinning oxidized Ti-6-4 Process Basics • Part and soldering iron tip must be heated • Typically 20-30°C above solder liquidus • Soldering iron tip must be wet with solder alloy • Soldering iron must be ultrasonically activated while in contact with the work piece • Both pieces are wetted with solder • Join while solder remains liquid or solidify and reflow

11. Advantages of Ultrasonic Soldering • Fluxless • No pre-fluxing • No post-cleaning • No corrosive flux residue • Ability to join “unsolderable” materials • Ferrous metals • Non-ferrous metals • Glasses • Ceramics • Graphite • Composites • No metalizing or plating required • Typically no controlled atmosphere required • Ability to join dissimilar materials

12. Heavily Oxidized Metals Glass-to-Metal Joint Ti-Al structural joint Ti 6-4 Al 2219 Key Advantages….Capable of Joining Dissimilar Materials • EWI patented Sn-based soldering alloy for difficult-to-wet material • Ti, Ni, Au, Ag, Pt, Al, Cu, SS, Fe, etc. • Al2O3, SiC, WC, BC, nitrides, etc. • Heavily oxidized or anodized metals • Glass, carbon foams, exotic materials 25-mm SiC to Ti-6-4 Glass-to-Ceramic Seal

13. Key Advantages….Selectively Solders Complex Shapes, Sizes Various shapes and sizes can be easily pretinned with SonicSolder™ and the ultrasonic soldering process 16- × 16-in. Ti-to-Ceramic Ballistic Panel Al to Cu Al Tube to Anodized Fitting

14. FEA analysis allows development of new sonotrodes tailored to specific applications Sample FEA Designs • In-house CAD design and machining expedites the developmental process Prototype Sonotrodes CAD Drawings EWI Expertise…. FEA-Aided Sonotrode Design

15. EWI SonicSolder™ • EWI developed a Sn-based soldering alloy for use on difficult to wet materials: • EWI-patented, high Sn solder alloy • Active metal addition enables wetting on Ti alloys, Al alloys, glass, and ceramics • Pb-free • All constituents are low-cost metals • Alloy is produced with conventional melting practices • Melting temperature ~230°C • Shear strengths up to 6 ksi • Higher strength modifications are possible

16. Case Study: Aluminum to Steel • Background: Lightweighting for automotive applications calls for joints between aluminum and steel sheet for deck lids and roof/pillar junctions • Problem: Aluminum and steel form brittle intermetallics when fusion- welded • Solution: Ultrasonically coat aluminum with Zn-Al alloy; spot-weld to galvanized steel • Result: Minimal intermetallic layer; shear strength up to 25 ksi

17. Case Study: Steel to Ceramic • Background: Demanding application requires wear-resistant SiC-diamond (SCD) ceramic bonded to steel • Problem: Joint geometry and CTE mismatch require low-temperature, high-strength bond • Solution: Use Zn-5Al alloy to ultrasonically solder ceramic to steel • Result: Average pushout force exceeds 15 ksi (10 ksi min force required) steel SCD Microstructure of SiC-diamond ceramic (courtesy of Element Six) C-scan image shows a sound joint

18. Case Study: ZAO to Stainless Steel • Background: Solar industry bonds zinc aluminum oxide (for thin-film PV) to stainless steel supports using indium + flux • Problem: Indium is expensive (~$20/oz) vs tin (~$0.60/oz) • Solution: Ultrasonically solder ZAO to SS using EWI SonicSolder™ • Result: Achieved shear strength of 2.7 ksi

19. Case Study: Titanium to Carbon Fibers • Background: Advanced aircraft incorporate titanium and carbon fiber composites for light, stiff structures • Problem: Conventional approaches such as adhesive bonding do not exhibit sufficient strength over the full operating temperature range • Solution: Ultrasonically solder CP Ti to graphite fiber tow using EWI SonicSolder™ • Result: Joints submitted to client for testing

20. Summary • Ultrasonic soldering is a fluxless process which works with any solid material • EWI SonicSolder™ has enabled joining of unique dissimilar material combinations • Higher-temperature solders have also been successfully used in ultrasonic joining • Extension into ultrasonic brazing (T > 450°C) has also been demonstrated (e.g. Al-Si, low-T Ag alloys)

21. Questions? Kirk Cooper Senior Engineer, Materials Email: kcooper@ewi.org Phone: 614.688.5069