September 14, 2011 Ultrasonic Soldering for Joining Dissimilar Materials Kirk Cooper Senior Engineer, Materials Phone:

What’s so exciting about soldering?

This is!

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?

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

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

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

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

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

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 Ultrasonic pretinning oxidized Ti-6-4 Hot Plate Electrically heated iron tip

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

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. ─Al 2 O 3, SiC, WC, BC, nitrides, etc. ─Heavily oxidized or anodized metals ─Glass, carbon foams, exotic materials Ti 6-4 Al 2219 Ti-Al structural joint 25-mm SiC to Ti-6-4 Glass-to-Ceramic Seal Glass-to-Metal Joint Heavily Oxidized Metals

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

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

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

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

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) Microstructure of SiC- diamond ceramic (courtesy of Element Six) steel SCD C-scan image shows a sound joint

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

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

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)

Questions? Kirk Cooper Senior Engineer, Materials Phone: