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Ultrasonic Soldering for Joining Dissimilar Materials September 14, 2011 Kirk Cooper Senior Engineer, Materials Email: [email protected] Phone: 614.688.5069 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 20-60 kHz Typical power levels <30 W Production equipment can be designed and constructed from commercial components Misonix 30-kHz soldering iron Bellex Int. 60-kHz soldering iron 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 Electrically heated iron tip 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 Hot Plate Ultrasonic pretinning oxidized Ti-6-4 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 ─ ─ ─ ─ Heavily Oxidized Metals 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 Glass-to-Metal Joint Ti-Al structural joint Ti 6-4 Al 2219 25-mm SiC to Ti-6-4 Glass-to-Ceramic Seal 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 EWI Expertise…. FEA-Aided Sonotrode Design FEA analysis allows development of new sonotrodes tailored to specific applications Sample FEA Designs In-house CAD design and machining expedites the developmental process CAD Drawings 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 fusionwelded Solution: Ultrasonically coat aluminum with Zn-Al alloy; spotweld to galvanized steel Result: Minimal intermetallic layer; shear strength up to 25 ksi Case Study: Steel to Ceramic Background: Demanding application requires wearresistant SiC-diamond (SCD) ceramic bonded to steel Problem: Joint geometry and CTE mismatch require lowtemperature, 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 SiCdiamond ceramic (courtesy of Element Six) 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 Email: [email protected] Phone: 614.688.5069