5th Annual IeMRC Conference
21st September 2010
Joining and Packaging Technology
for High Temperature Electronics
Beyond Solder?
Norman Stockham
TWI
Technology Engineering
Copyright © TWI Ltd 2010
TWI
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Technology Engineering
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High Temperature Electronics
Electronics & sensors are increasingly being applied for
monitoring & control in high temperature harsh environments
Higher ambient temperatures:
200-400°C
400-800°C
Increased exposure to chemically active environments:
- Humidity
- Brake fluid
- Salt spray - Exhaust gases
- Fuel
- Radiation
- Oil
- Body fluids
Industry sectors:
- Automotive - Power
- Aerospace - Military
Bore hole data logger
- Oil & Gas - Medical
- Construction
Technology Engineering
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Device & Substrate Temperature
Tolerance*
Device
Temp
tolerance °C*
Silicon (Si)
125-250
Silicon-oninsulator (SOI)
250-300
Gallium Arsenide
(GaAs)
350
Gallium Nitride
(GaN)
>500
Silicon Carbide
(SiC)
>750
Diamond
>800
* Scatter exists in the values in literature
Technology Engineering
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
Copyright © TWI Ltd 2010
Joining Technologies for High
Temperatures >200°C
•
•
•
•
•
•
•
Solder
Adhesives
Welding
Brazing
Glass
Mechanical
Disruptive
Technology Engineering
Die/substrate attach
Device interconnect
Package sealing
Package interconnect
Copyright © TWI Ltd 2010
Solder Applications - Electronics
Heat sink attach
Track repair
Package attach
Die attach
Passive
component
attach
Connectors
Device Interconnect
Package sealing
Substrate Attach
EMI shielding attach
Selective device soldering
Technology Engineering
Device Alignment
Copyright © TWI Ltd 2010
Benefits of Solder
•
•
•
•
•
•
•
6000 years experience
Relatively low melting point
Very high production volume capability
Electrical and thermal conductivity
Reworkable
Joint gap tolerant
Courtesy British Museum
Self aligning
Many electronic components and
materials are designed for soldering
Technology Engineering
Copyright © TWI Ltd 2010
Typical Solder & Braze Alloys
Alloy
99Cu-1Ag
100Au
82Au-18Ni
60Au-20Cu-20Ag
91.5Cu-2Ag-6.5P
58Au-42In
95Pb-25Pd
48Al-52Ge
97Au-3Si
88Au-12Ge
Melting Point/Range ºC
1070 - 1080
1064
955
835 - 845
643 - 796
495
454
424
363
356
95Pb-5Sn
300-315
1Sn-2Ag-97Pb
80Au-20Sn
99Sn-1.0Cu
96.5Sn-3.5Ag
95.5Sn-3.8Ag-0.7Cu
63Sn-37Pb
62Sn-36Pb-2Ag
295-320
280
227
221
217
183
179
Technology Engineering
>450°C Braze
High
Temperature
Solders
Conventional
Electronics
Solders!
Copyright © TWI Ltd 2010
Device & Substrate Attach
Joining Methods:
• Solder
• Adhesive
• Brazing
• Glass
• Anodic bonding
• Mechanical
• Diffusion bonding
• Welding
• Novel
Technology Engineering
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Device & Substrate Attach
Design Issues/Considerations
Technology Engineering
40
24.5
FR-4
Copper
Aluminium
0
94% Alumina
6.4
10
5.9
4.5
4
3
Silicon
15.8
SiC
17
AlN
19
20
Kovar
30
Low stress epoxy 'Glob top'
• Thermal Conductivity,
(Solder: 30-50 W/mK)
50
50
Epoxy
• Operating temperature
capability
(eg >200°C)
60
CTE (x10-6 in/in/°C)
• Differential thermal
expansion causes
deformation & stress
Coefficient of thermal expansion
Copyright © TWI Ltd 2010
Device & Substrate Attach
Adhesive Die (Chip) Attach
Level of adhesive use: Extensive
Reasons for adhesive use:
- Low cost
- Ease of assembly
- Tailored properties (mechanical/electrical)
- No plating
Si die to Al2O3 substrate
- Low temperature processing (low stress)
- Electrical/thermal conductivity (solder)
- Stress absorption
- Rework possible
Typical adhesive die attach materials:
Flip Chip Bonding
- Acrylics, Epoxies & Polyimides (eg silver filled)
Technology Engineering
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Device & Substrate Attach
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
TP
Thermoset
Thermoplastic
*
Dependent on environment and operation
Technology Engineering
Copyright © TWI Ltd 2010
Device & Substrate Attach
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
Technology Engineering
Copyright © TWI Ltd 2010
Device & Substrate Attach
Liquid Phase Joining
Brazing
90mm Φ Silicon Carbide to Tungsten
Active metal braze
Direct Copper Bonding
Copper to Alumina
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).
Application of heat and pressure
in an oxygen rich environment.
Copper oxidises and forms
eutectic liquid (Cu2O) at 1070°C.
Requires flux or a protective atmosphere.
Technology Engineering
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Device & Substrate Attach
Solid Phase Joining
Ultrasonic Welding
Aluminium to Alumina
Diffusion Bonding
Alumina-copper with gold interlayer
Friction Welding
Electrostatic Bonding
Aluminium to Alumina
Silicon to Pyrex
Technology Engineering
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Device & Substrate Attach
Reducing CTE Stress via Interlayers
Silicon Nitride to Steel
Technology Engineering
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Device & Substrate Attach
Carbon Nanotube (CNT) Interfaces
High thermal conductivity ~1000 - 3000 W/mK
CNT composite
adhesive
Tin
High power chip
Heat sink
Tout
MWCNT Mat
Top
Technology Engineering
Side
Overview
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Device & Substrate Attach
Spray Coating Technologies: Reduce Interfaces
HVOF Spray
Cu-Al2O3
Technology Engineering
Cold Spray
W-Cu Blend
Cu Heat Sinks
Copyright © TWI Ltd 2010
Device & Substrate Attach
Moulded Al2O3 / Al-SiC MMC Package
Embedded
Al2O3
substrate
Al-SiC
package
Conventional
Al2O3
substrate
Technology Engineering
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Device to Package Interconnect
Interconnect Methods:
• Wire bonding
• Flip chip bonding
• Soldering
• Adhesives
• Welding
• Mechanical
Technology Engineering
Copyright © TWI Ltd 2010
Device to Package Interconnect
Wire Bonding
•
•
•
•
Mature technology
High process yields
Design flexibility
Increasing power
capability
• High temp capability
Au ball bonding
Ribbon Bonding
Power Device Bonding
Courtesy of Orthodyne Electronics
Needs Protection
Cu ball bonding
Technology Engineering
Al ball bonding
Copyright © TWI Ltd 2010
Device to Package Interconnect
Wire Bonding Service Temperatures
Upper continuous
Wire
Pad
service temperature ºC *
Au
Al
~150-180
Cu
Al
~200
Al
Ni
~300
Pd
Au
~500
Al
Al
~600
Au
Au
~1000
Pt
Pt
>1000
Interdiffusion
Brittle intermetallics
Increased resistance
Loss of strength
Melting temperature
* Influenced by environment and metallisation system
Technology Engineering
Copyright © TWI Ltd 2010
Device to Package Interconnect
Alternative Interconnect Processes
• Flip Chip Bonding/Welding
- Adhesives
- Thermocompression
Flip chip bonding
• Conductive Adhesives + leadframe
• Mechanical
Silicon Nitride Microclips
Courtesy University of Cambridge
• Direct write/print?
• Laser & Resistance Welding
(wire, leadframe, beam lead):
Technology Engineering
Microjet
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Package Sealing/Protection
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
Technology Engineering
Metal housings
Polymer housing
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Package Sealing/Protection
Outer Package Materials – Operating Temperatures
Typical continuous
Metal
Typical continuous service
temp ºC *
Copper
200
(oxidation)
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)
260
Nickel/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 (-)
Polymer
service temp ºC *
Polypropylene (TP)
(glass reinforced)
105-125
Polycarbonate (TP)
TS = Thermoset / TP = Thermoplastic
* Dependent on environment
Technology Engineering
Copyright © TWI Ltd 2010
Package Sealing/Protection
Conventional Hermetic Sealing Processes
Power supply
Resistance Seam Sealing
- Brazing
Electrode
Lid
Base
Work table
Laser & Electron Beam Welding
Electron Beam Welding
Technology Engineering
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Package Sealing/Protection
Anodic Bonding/Wafer Level Packaging
Typical Parameters:
Temp: 200-500°C
Voltage: 200-2000 Vd.c.
Time: 10s-120min
Polarity: glass negative
MEMS RF
module
Technology Engineering
Copyright © TWI Ltd 2010
Package External Interconnect
Joining Methods:
• Soldering
• Conductive Adhesives
• Welding
• Brazing
• Mechanical
Technology Engineering
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Package External Interconnect
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
Adhesive SMT
Typical conducting adhesive for solder replacement
-
Ag filled epoxies
Technology Engineering
ACA display Interconnect
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Package External Interconnect
Replacement of Solder by Welded Terminations
Resistance
TIG
Wire and leadframe
Percussive arc
Wire to pin connections
Technology Engineering
Coil Windings
Ultrasonic
Wire terminations
Laser
Ultrasonic
Lead frame assembly
(Courtesy of Amtech)
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Package External Interconnect
Friction Acoustic Bonding
Load
Rotation
Traverse Speed
Copper ribbon cable to PCB
Typical Materials: Aluminium
Copper
Steel
Polymers
Technology Engineering
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Package External Interconnect
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
Technology Engineering
Copyright © TWI Ltd 2010
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
Technology Engineering
Copyright © TWI Ltd 2010
Disruptive Technology
High Density Packaging
Stacked Die Packaging
Typical thicknesses:
Die:
40-70µm
Adhesive: 10-20µm
Package: 1.4mm
Courtesy of ASE Group
Technology Engineering
Embedded Passive Devices
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
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Disruptive Technology
System in Package (SiP)
SiP to pcb
interconnections
Flip chip
device
internal
SiP package
interconnection
wire bond
Passive
device
component
PCB
SiP ID
screening
thermal dissipation
Package
in
Package
Technology Engineering
Copyright © TWI Ltd 2010
Summary & Conclusions
General Thermal Hierarchy
Typical upper operating
Material
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
Technology Engineering
Copyright © TWI Ltd 2010
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.
Technology Engineering
Copyright © TWI Ltd 2010
Thank you
I hope you enjoyed this
presentation
Norman Stockham
TWI
Granta Park
Cambridge, UK
Tel: +44 (0)1223 899323
Email: norman.stockham@twi.co.uk
Technology Engineering
Copyright © TWI Ltd 2010