September 14, 2011 Ultrasonic Soldering for Joining Dissimilar Materials Kirk Cooper Senior Engineer, Materials Email: [email protected]@ewi.org Phone:

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