Joining and Packaging Technology for High Temperature ......• Adhesive •Brazing •Glass • Anodic bonding • Mechanical • Diffusion bonding • Welding ... •Wire bonding

Copyright © TWI Ltd 2010Technology Engineering

5th Annual IeMRC Conference

21st September 2010

Joining and Packaging Technology for High Temperature Electronics

Beyond Solder?

Norman Stockham

TWI


TWI

• Independent R&T organisation

• Specialising in materials, joining,

assembly, training & technology

transfer

• Limited by guarantee/non-profit

distributing

• 3500 industrial member sites in 75

countries

• 580 staff, £58M turnover

Brazil

UK

UAE

China

Thailand

Indonesi

a

Malay

sia Kuching

SingaporeIndia

Houston

Vietnam

Bahrain

Brazil

Egypt

India

Japan

KoreaKuwait

Qatar

Taiwan

Algeria

Italy

Saudi Arabia

Turkey

Australia

Ukraine

USA

Cambridge

Middlesbrough Port Talbot Aberdeen

Sheffield

5 UK Technology Centres

Bahrain

Korea

Vietnam Johor Bahru

8 International FacilitiesKuala Lumpur


High Temperature Electronics

Higher ambient temperatures:

200-400°C 400-800°CIncreased exposure to chemically active environments:

- Humidity - Brake fluid

- Salt spray - Exhaust gases

- Fuel - Radiation

- Oil - Body fluids

Industry sectors:

- Automotive - Power

- Aerospace - Military

- Oil & Gas - Medical

- Construction

Electronics & sensors are increasingly being applied formonitoring & control in high temperature harsh environments

Bore hole data logger


Device & Substrate Temperature Tolerance*

Device

Temp

tolerance °C*

Silicon (Si) 125-250

Silicon-on-

insulator (SOI)

250-300

Gallium Arsenide

(GaAs)

350

Gallium Nitride

(GaN)

>500

Silicon Carbide

(SiC)

>750

Diamond >800

* Scatter exists in the values in literature

Substrate Material

Typical max

use temp °C*

Epoxy-glass (FR4) 110-140

Bismaleimide Triazine (BT)

Epoxy

180-190

PTFE-glass 170-200

Polyimide-Quartz 250-280

Alumina (Al2O3) >1000

Silicon carbide (SiC) >1000

Silicon (Si) ~1000

Aluminium (Al) 660

Al-Si MMC

Copper 1083

Ni-Fe-Co (Kovar) 1450

Stainless steel 1400-1500

*Dependent on environment/grade/metallisation etc


Joining Technologies for High Temperatures >200°C

• Solder

• Adhesives

• Welding

• Brazing

• Glass

• Mechanical

• Disruptive

Die/substrate attach

Device interconnect

Package sealing

Package interconnect


Solder Applications - Electronics

Die attach

EMI shielding attach

Heat sink attach

Package sealing

Selective device soldering

Track repair

Device Alignment

Substrate Attach

Passive

component

attach

Device Interconnect

Connectors

Package attach


Benefits of Solder

• 6000 years experience

• Relatively low melting point

• Very high production volume capability

• Electrical and thermal conductivity

• Reworkable

• Joint gap tolerant

• Self aligning

Many electronic components and materials are designed for soldering

Courtesy British Museum


Typical Solder & Braze Alloys

48Al-52Ge 424High

Temperature

Solders

97Au-3Si 363

88Au-12Ge 356

95Pb-5Sn 300-315

Alloy Melting Point/Range ºC

99Cu-1Ag 1070 - 1080

>450°C Braze

100Au 1064

82Au-18Ni 955

60Au-20Cu-20Ag 835 - 845

91.5Cu-2Ag-6.5P 643 - 796

58Au-42In 495

95Pb-25Pd 454

1Sn-2Ag-97Pb 295-320

Conventional

Electronics

Solders!

80Au-20Sn 280

99Sn-1.0Cu 227

96.5Sn-3.5Ag 221

95.5Sn-3.8Ag-0.7Cu 217

63Sn-37Pb 183

62Sn-36Pb-2Ag 179


Device & Substrate Attach

Joining Methods:

• Solder

• Adhesive

• Brazing

• Glass

• Anodic bonding

• Mechanical

• Diffusion bonding

• Welding

• Novel



Design Issues/Considerations

• Differential thermal

expansion causes

deformation & stress

• Operating temperature

capability

(eg >200°C)

• Thermal Conductivity,

(Solder: 30-50 W/mK) Coefficient of thermal expansion

50

24.519 17 15.8

6.4 5.9 4.5 4 3

0

10

20

30

40

50

60

Epoxy

Alu

min

ium

Low

str

ess e

poxy 'G

lob top'

Copper

FR

-4

94%

Alu

min

a

Kovar

AlN

SiC

Silicon

CT

E (

x10-6

in/in/°

C)



Adhesive Die (Chip) AttachLevel of adhesive use: Extensive

Reasons for adhesive use:

- Low cost

- Ease of assembly

- Tailored properties (mechanical/electrical)

- No plating

- Low temperature processing (low stress)

- Electrical/thermal conductivity (solder)

- Stress absorption

- Rework possible

Typical adhesive die attach materials:

- Acrylics, Epoxies & Polyimides (eg silver filled)

Si die to Al2O3 substrate

Flip Chip Bonding



Typical Adhesives

Polymer type

Typical maximum

continuous service

temp ºC *

Chemical and

solvent resistances *

Polyurethane (TS, TP) 95 Poor

Epoxy (TS) 120-200 Excellent

Phenolic (TS) 150-250 Good

Polyimide (TS) 260 Excellent

Silicone (TS) 260 Good

Polyamide-imide (TP) 270 Good

TS Thermoset

TP Thermoplastic

* Dependent on environment and operation



Eutectic Die Attach

Gold-Silicon Eutectic Die Attach:

Eutectic composition: 3%Si, MP 363°C

Thermal Conductivity: 60 W/mK

Issues: Stress on large die

Typically: Used on small die (<8 x 8mm)

Ceramic packages

Die backside Au metallised

Can employ Au or Au-2%Si preforms

Process temperature: 425°C

Scrubbing to disrupt Si Oxide

Hot (eg 175°C) nitrogen blanket



Liquid Phase Joining

Fusible metal alloy >450°C.

Application of heat to reflow braze alloy.

Braze metals with/without metallisation.

Ceramics, usually metallised (eg Mo/Mn, Sputter coating, thick film).

Ceramics can be brazed directly using active braze materials (eg Ti additive).

Requires flux or a protective atmosphere.

90mm Φ Silicon Carbide to Tungsten

Active metal braze

Brazing

Application of heat and pressure

in an oxygen rich environment.

Copper oxidises and forms

eutectic liquid (Cu2O) at 1070°C.

Copper to Alumina

Direct Copper Bonding



Solid Phase Joining

Friction Welding

Ultrasonic Welding

Alumina-copper with gold interlayer

Diffusion Bonding

Aluminium to Alumina

Electrostatic Bonding

Silicon to PyrexAluminium to Alumina



Reducing CTE Stress via Interlayers

Silicon Nitride to Steel



Carbon Nanotube (CNT) Interfaces

MWCNT Mat

Top Side Overview

Tout

High power chip

Heat sink

Tin

CNT composite

adhesive

High thermal conductivity ~1000 - 3000 W/mK



Spray Coating Technologies: Reduce Interfaces

Cold SprayHVOF Spray

Cu-Al2O3W-Cu Blend Cu Heat Sinks



Moulded Al2O3 / Al-SiC MMC Package

Embedded

Al2O3

substrate

Al-SiC

package

Conventional

Al2O3

substrate


Device to Package Interconnect

Interconnect Methods:

• Wire bonding

• Flip chip bonding

• Soldering

• Adhesives

• Welding

• Mechanical



Wire Bonding

Cu ball bonding

Ribbon Bonding

Al ball bonding

• Mature technology

• High process yields

• Design flexibility

• Increasing power

capability

• High temp capability

Needs Protection

Power Device Bonding

Courtesy of Orthodyne Electronics

Au ball bonding


Wire Pad

Upper continuous

service temperature ºC *

Au Al ~150-180Interdiffusion

Brittle intermetallics

Increased resistance

Loss of strength

Cu Al ~200

Al Ni ~300

Pd Au ~500

Al Al ~600

Melting temperatureAu Au ~1000

Pt Pt >1000

* Influenced by environment and metallisation system


Wire Bonding Service Temperatures



Alternative Interconnect Processes

• Flip Chip Bonding/Welding

- Adhesives

- Thermocompression

• Conductive Adhesives + leadframe

• Mechanical

• Direct write/print?

• Laser & Resistance Welding

(wire, leadframe, beam lead):

Flip chip bonding

Silicon Nitride Microclips

Courtesy University of Cambridge

Microjet


Package Sealing/Protection

Metal housings

Polymer housing

Hermetic Packaging, eg:

Kovar, plated lids

Aluminium alloy

Stainless steel

Titanium

Copper

Ceramic

Glass

Non Hemetic (Polymer), eg:

Polymer housing

Potting

Glob top

Conformal coating


PolymerTypical continuous

service temp ºC * MetalTypical continuous service

temp ºC *

Polypropylene (TP)

(glass reinforced)105-125

Copper 200 (oxidation)

Polycarbonate (TP) 120 Al alloys 300 (creep)

PPA (TP) 190 Nickel irons 400 (oxidation)

LCP (Polyester) (TP) 240 Titanium 600 (oxidation)

PEEK (TP) 250 Stainless steels 800 (oxidation)

PPS (TP) 260Nickel/colbalt heat

resistant alloys

1000 (creep)

Polyimide (TS) 260 Ceramic

PTFE (TP) 285 Glass ceramic 600-700 (strength reduction)

SiC 700-800 (degradation)

Al2O3 800 (creep)

Sapphire 1500-1600 (-)

TS = Thermoset / TP = Thermoplastic* Dependent on environment


Outer Package Materials – Operating Temperatures



Conventional Hermetic Sealing Processes

Resistance Seam Sealing

- Brazing

Laser & Electron Beam Welding

Electron Beam Welding

Power supply

Work table

Electrode Lid

Base



Anodic Bonding/Wafer Level Packaging

MEMS RF

module

Typical Parameters:

Temp: 200-500°C

Voltage: 200-2000 Vd.c.

Time: 10s-120min

Polarity: glass negative


Package External Interconnect

Joining Methods:

• Soldering

• Conductive Adhesives

• Welding

• Brazing

• Mechanical



Replacement of Solders by Conductive Adhesives

Reasons for adhesive use:

- Environmental (Pb-free)

- Low processing temperature

- Fine pitch capability (eg: ACA)

Primary choice issues:

- Long term reliability

- Electrical conductivity

- Mechanical strength

- Alignment/Co-planarity of leads/board

Typical conducting adhesive for solder replacement

- Ag filled epoxies

Adhesive SMT

ACA display Interconnect



Replacement of Solder by Welded Terminations

Ultrasonic

Percussive arc

TIG

Coil Windings

Lead frame assembly

Wire to pin connectionsWire terminations(Courtesy of Amtech)

Wire and leadframe

Resistance

Laser

Ultrasonic



Friction Acoustic Bonding

Typical Materials: Aluminium

Copper

Steel

Polymers

Copper ribbon cable to PCB

Load

Rotation

Traverse Speed



Replacement of Solder by Welded Terminations

• High temperature capability

• Low resistance joints

• Reduced footprint

• No plating/intermediary material costs

• No soldering flux/residues/cleaning chemicals

• Automated processes

• No ‘contaminants’ when recycled


Replacement of Solders by Disruptive Technology

Remove joints!

• Increase active device functionality

• Reduce number of interfaces

• Hybrid/COB type technologies

• 3D, SiP

• Wafer scale packaging


Disruptive Technology

High Density Packaging

Benefits:

• Improved performance

• Reduced size & weight (2 to 10 times)

• Fewer SMT components, faster throughput

• Reduced costs per function

• Reduced external wiring

• Improved reliability & EMC emissions

Embedded Passive Devices

Typical thicknesses:

Die: 40-70µm

Adhesive: 10-20µm

Package: 1.4mm

Stacked Die Packaging

Courtesy of ASE Group


Disruptive Technology

System in Package (SiP)

PCB

Flip chip

deviceSiP to pcb

interconnections

thermal dissipation

SiP IDwire bond

devicePassive

component

SiP packageinternal

interconnection

screening

Package in

Package


Material

Typical upper operating

temperature ºC *

Adhesives (conductive) 250

Soldering 250

Glass Fusion 350-1000

Brazing 450-1100

Ceramic Adhesives 200-1500

Welding 200-2000

* Dependent on materials and application

Summary & Conclusions

General Thermal Hierarchy


Summary and Conclusions

• Solder technology is not easily replaced in the high volume PCB assembly market

• Solder has to a large extent been replaced in die attach, device interconnect & package sealing.

• There will be a reduction in solder joints as a consequence of on going drivers in electronics aimed at:

– increasing product performance (eg: density & operating temp.)

– reducing size

– tightening environmental legislation

• There are alternatives to solder for higher temperature applications (eg >200ºC). However, these have to be considered at an early design stage in conjunction with device & packaging materials, interconnect, layout and production requirements.


Thank you I hope you enjoyed this

presentationNorman Stockham

TWI

Granta Park

Cambridge, UK

Tel: +44 (0)1223 899323

Email: [email protected]

Documents

Joining and Packaging Technology for High Temperature ......• Adhesive •Brazing •Glass • Anodic bonding • Mechanical • Diffusion bonding • Welding ... •Wire bonding