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Copyright © TWI Ltd 2008World Centre for Materials Joining Technology

Joined for LifeJoined for LifeStateState--ofof--thethe--art joining processes, from art joining processes, from chip interconnect to package sealingchip interconnect to package sealing

Developments in Interconnect, Developments in Interconnect, Assembly and Packaging WorkshopAssembly and Packaging Workshop

Helen Helen GoddinGoddin


Joining in MicroelectronicsJoining in Microelectronics•• TWI TWI MicrotechnologyMicrotechnology section deals with section deals with

joining, materials selection and design at all joining, materials selection and design at all levels of microelectronics manufacturelevels of microelectronics manufacture


OverviewOverviewWhat trends have there been for joining in microelectronics?


OverviewOverview

Wire bonding

Flip chip

Laser welding

Friction stir welding


OverviewOverview

Wire bonding

Flip chip

Laser welding

Friction stir welding

Reliability Testing

System in package


Joining Trends and IssuesJoining Trends and Issues•• MiniaturisationMiniaturisation

–– ManipulationManipulation–– Sensitivity to parametersSensitivity to parameters–– ReworkRework–– TestingTesting–– GeometryGeometry

•• LegislationLegislation•• New materialsNew materials•• Increasing automation and speedIncreasing automation and speed•• Thermal managementThermal management•• ReliabilityReliability


Wire bondingWire bonding•• Gold and aluminium wire bonding still makes Gold and aluminium wire bonding still makes

up large percentage of bonds made todayup large percentage of bonds made today•• Copper still of interest, some companies Copper still of interest, some companies

looking to put into manufacturelooking to put into manufacture•• Increased interest with Increased interest with

inin--situsitu monitoringmonitoring


Sensor

Digital Ultrasonic Generator

Actuator

• Mechanical Oscillations• Friction

PiQC-Signals

• Wire Deformation

• Current• Frequency

PiQCPiQC


Potential ApplicationsPotential Applications•• Identifying suspicious bonds (e.g. pad contamination, Identifying suspicious bonds (e.g. pad contamination,

scratches, misalignment)scratches, misalignment)•• Selecting conditions for fine wireSelecting conditions for fine wire

Contaminated bonds are represented by contours inside the map

Good bonds are located at the outer border of the map (100%)


Flip ChipFlip Chip

•• Use of flip chip projected to continue to growUse of flip chip projected to continue to grow•• Advantages:Advantages:

–– SizeSize–– PerformancePerformance–– FlexibilityFlexibility–– ReliabilityReliability–– Cost over other packaging methods.Cost over other packaging methods.–– Widening availability in flip chip materials, equipment, Widening availability in flip chip materials, equipment,

and servicesand services


Future ApplicationsFuture Applications•• OptoOpto--electronic devices.electronic devices.

•• XX--byby--wire automotive control systems. wire automotive control systems. ‘‘XX’’ represents the represents the basis of safetybasis of safety--related applications such as steering, related applications such as steering, braking, braking, powertrainpowertrain, suspension control, collision , suspension control, collision avoidance.avoidance.

•• High brightness LEDs are a potential future market for High brightness LEDs are a potential future market for flip chip. This will allow high currents and higher flip chip. This will allow high currents and higher brightness to be achieved.brightness to be achieved.

•• Digital TV marketDigital TV market


TWI and Flip ChipTWI and Flip Chip

•• Internal projects to assess technology Internal projects to assess technology •• Involvement in collaborative projects to support Involvement in collaborative projects to support

flip chip developmentflip chip development•• Prototyping for membersPrototyping for members

Bumped Silicon IC


TWI FacilitiesTWI Facilities•• BumpingBumping

–– stud bumpingstud bumping–– infrastructure evaluationinfrastructure evaluation–– bumping accessbumping access

•• Flip chip assemblyFlip chip assembly–– equipment evaluationequipment evaluation–– thermocompression thermocompression –– solder flip chipsolder flip chip–– adhesive flip chipadhesive flip chip–– process developmentprocess development–– device prototypingdevice prototyping

Soldered flip chip interconnection


Laser WeldingLaser Welding•• Well established in industry for Well established in industry for

package sealingpackage sealing•• Particularly titanium packages for Particularly titanium packages for

pacemakers and implantable pacemakers and implantable devicesdevices

•• Smaller spot size lasers now Smaller spot size lasers now availableavailable

•• Potential for welding leads on Potential for welding leads on packages (plated copper) dual packages (plated copper) dual wavelength lasers wavelength lasers

•• Aluminium alloy packages for Aluminium alloy packages for microwave applicationsmicrowave applications

•• Small thickness foils for electrical Small thickness foils for electrical interconnectionsinterconnections

GSI GSI LumonicsLumonicsNd:YAGNd:YAG

Welding/cuttingWelding/cutting


Micro Friction Stir Welding Micro Friction Stir Welding

TWI desktop TWI desktop μμFSW machineFSW machine2.5D CNC, 302.5D CNC, 30μμm accuracy, max m accuracy, max ωω = 24,000rpm, max = 24,000rpm, max νν = 6m/min= 6m/min


μμFSW AdvantagesFSW Advantages•• Exploit FSW for thin materials in:Exploit FSW for thin materials in:

–– electronics, photonics, automotive, aerospace, electronics, photonics, automotive, aerospace, consumer products, medical, power consumer products, medical, power …………

•• SingleSingle--pass, solidpass, solid--phase ambient joining phase ambient joining •• Environmentally and cleanroom friendlyEnvironmentally and cleanroom friendly

–– No chemical cleaningNo chemical cleaning–– No preNo pre--platingplating–– No added filler materialsNo added filler materials–– Low energy consumptionLow energy consumption

•• Fast, simple yet reliableFast, simple yet reliable•• Low capital with low consumablesLow capital with low consumables•• Efficient and low H&S riskEfficient and low H&S risk•• Small heat affected zoneSmall heat affected zone•• Unexplored potentialsUnexplored potentials

–– Metals, ceramics, plastics, compositesMetals, ceramics, plastics, composites–– Packaging, hermetic sealing, Packaging, hermetic sealing, microjoiningmicrojoining–– Butt, overlap & spot welding Butt, overlap & spot welding


Example application: Package sealingExample application: Package sealing

Fibre-optic receivers & transmitters


Example application: InterconnectionExample application: Interconnection

Ribbon & heavy-wire bonding


Reliability TestingReliability Testing•• Thermal cycling, thermal aging, Thermal cycling, thermal aging,

highly accelerated stress highly accelerated stress testing, power cyclingtesting, power cycling……..

•• Well established standards for Well established standards for different types of testing (e.g. different types of testing (e.g. JEDEC)JEDEC)


Reliability TestingReliability Testing•• Now emphasis on understanding Now emphasis on understanding

mechanisms of failure with minimum mechanisms of failure with minimum testing on smaller components testing on smaller components →→Precision Reliability Testing Precision Reliability Testing

•• Miniaturisation Miniaturisation →→ higher current higher current densities densities →→ electromigrationelectromigration in joints in joints as well as filmsas well as films


Al3Au8 AlAu2

AlAu4

Al3Au8

AlAu4voids Au

Au

Si

Si

voids

ElectromigrationElectromigration in Wire bondsin Wire bonds

AlAu2

AlAu4

Al3Au8

AlAu4Al3Au8

AlAu2

voids

voids

Si

Au

Au

Si

20μm


System in PackageSystem in Package

motherboard

Integrated passives

Active devices•• ADEPTADEPT--SiPSiP

Right first time design process


SummarySummary•• Joining continues to be one of the key Joining continues to be one of the key

challenges in microelectronics packaging challenges in microelectronics packaging •• Wire bonding inWire bonding in--situ monitoring important, situ monitoring important,

new new PiQCPiQC sold by sold by HesseHesse & & KnippsKnipps•• Lasers reducing in spot size, possible Lasers reducing in spot size, possible

applications in lead weldingapplications in lead welding•• Micro friction stir welding applications Micro friction stir welding applications

package sealing and lead weldingpackage sealing and lead welding•• ElectromigrationElectromigration in joints now importantin joints now important•• System in package design can maximise System in package design can maximise

board usage but must be board usage but must be ““right first timeright first time””

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