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September 14, 2011
Ultrasonic Soldering for Joining Dissimilar Materials
Kirk CooperSenior Engineer, MaterialsEmail: [email protected]: 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
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.─ Al2O3, 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
CADDrawings
FEA analysis allows development of new sonotrodes tailored to specific applications
In-house CAD design and machining expedites the developmental process
PrototypeSonotrodes
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 CooperSenior Engineer, MaterialsEmail: [email protected]: 614.688.5069