advances & challenges in high temperature component attachment
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1
Cheryl Tulkoff, ASQ CRE
DfR Solutions
February 9, 2012
Advances & Challenges in High
Temperature Component
Attachment
Houston SMTA Expo Feb 2012
2
Cheryl’s Background
o 22 years in Electronics
o IBM, Cypress Semiconductor, National Instruments
o SRAM and PLD Fab (silicon level) Printed Circuit Board Fabrication, Assembly, Test, Failure Analysis, Reliability Testing and Management
o ISO audit trained, ASQ CRE, Senior ASQ & IEEE Member
o Random facts:
o Rambling Wreck from Georgia Tech
o 14 year old son David, Husband Mike, Chocolate Lab Buddy
o Marathoner & Ultra Runner
o Ran Boston 2009 in 3:15
o Ran 100 miles in 24:52 last weekend 2/4-2/5,2012
o Triathlete – Sprint, Olympic, and Half. Ironman finisher in CDA, Idaho in June ‘10
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Biography
o Cheryl Tulkoff has over 20 years of experience in electronics manufacturing with an emphasis on failure analysis and reliability. She has worked throughout the electronics manufacturing life cycle beginning with semiconductor fabrication processes, into printed circuit board fabrication and assembly, through functional and reliability testing, and culminating in the analysis and evaluation of field returns. She has also managed no clean and RoHS-compliant conversion programs and has developed and managed comprehensive reliability programs.
o Cheryl earned her Bachelor of Mechanical Engineering degree from Georgia Tech. She is a published author, experienced public speaker and trainer and a Senior member of both ASQ and IEEE. She holds leadership positions in the IEEE Central Texas Chapter, IEEE WIE (Women In Engineering), and IEEE ASTR (Accelerated Stress Testing and Reliability) sections. She chaired the annual IEEE ASTR workshop for four years and is also an ASQ Certified Reliability Engineer.
o She has a strong passion for pre-college STEM (Science, Technology, Engineering, and Math) outreach and volunteers with several organizations that specialize in encouraging pre-college students to pursue careers in these fields.
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Background
o Long-time need for high temperature materials for component attachment o Industrial controls
o Space
o Oil drilling
o Requirements
o Ease of assembly
o Creep resistant
o Low cost
o Pb-free (yes!)
o Need to rethink past approaches
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High Temperature Solder (HTS): Definition
o What is “High Temperature”?
o Melting temperature?
o Operational temperature?
o Melting temperature
o Above SnPb (Tmelt > 183C)
o Above ‘standard’ Pb-free (Tmelt > 217C)
o Operational temperatures
o Above 75C – 125C
o Some companies limit SnPb solder temps to 75C
o Accelerated tests above 125C can produce anomalous results
o Categorization (150C / 200C / 250C / 300C)
6
High Temperature Solder (HTS): Definition
o What is Solder?
o A metal that joins two items together through the process of
melting and intermetallic formation
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o It’s not just about high temperature!
o Electronics used in oil, gas, and geothermal wells are exposed to some of the most severe use conditions out there:
o Temperatures: 300°C continuous; 350°C peak
o Vibration: PSD (power spectral density, g2/Hz) = 0.01 - 0.1 (0.6 - 3 kHz)
o Corrosion: H2S and H2 gas, salt, superheated steam
o Pressures: 15,000 to 30,000 psi
o Automotive electronics environment also very harsh
o Sensors used in: Combustion : <500°C, Exhaust : <800°C
o Engine: Transmission: <200°C
o Engine Compartment: <150°C
o Powertrain, Transmission Control, Vehicle Dynamic Control
Broaden the Scope: Severe or Harsh Electronic Conditions
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Outline
o Traditional approach
o High Pb Solders
o Variation on traditional approach
o High temp alloys with no Pb
o Alternative approaches
o Occam (Verdant): solder free
o Adhera Technologies
o Liquid phase sintering
o Reactive foils (Indium Nano Foil & Nano Bond)
o High temperature conductive film (B-Tech)
9
SnPb System
o Most popular
o Good wettability
o Only Sn is involved in the actual soldering
o Pb influences wetting, mechanical properties, and melt temp.
o High-temperature alloys available at Sn-rich and Pb-rich areas of phase diagram
o Greatest interest in Pb-rich phases (≥85Pb)
o Extensive alloying for property modification
o RoHS exemption
Alloy Solidus (ºC) Liquidus (ºC)
Sn 232 232
Sn5Pb 183 222
Sn10Pb 183 213
Sn20Pb 183 199
Sn37Pb 183 183
Sn50Pb 183 212
Sn60Pb 183 234
Sn70Pb 183 255
Sn80Pb 183 275
Sn85Pb 225 290
Sn90Pb 275 302
Sn95Pb 308 312
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High Pb Alloys
o Most alloys maintain 5 to 10%
Sn
o Flip-chip in component: Sn97Pb
or Sn95Pb
o Ceramic ball grid array
(CBGA): Sn90Pb
o Column grid array (CGA):
Sn90Pb
o Die attach: Sn92.5Pb2.5Ag
o Common alloying elements
o Silver (Ag), Indium (In),
Antimony (Sb)
o 0.5 to 10%
Alloy Solidus
(ºC)
Liquidus
(ºC)
Sn83Pb10Sb2Ag 237 247
Sn85Pb10Sb 245 255
Sn88Pb2Ag 267 290
Sn90Pb5Ag 292 292
Sn95.5Pb2.5Ag 299 304
Sn96Pb2Sb 305 315
Pb5In 300 313
Pb10Sb 252 260
Pb5Sb 252 295
Pb(2-5)Ag 303 303
Pb5In5Ag 290 310
11
Binary and Ternary Pb-Free Alloys
o Default alloys for Pb-free commercial electronics
o Moderate improvement in maximum use temperature
o +30C to +50C
o Manufacturing issues
o Reduced margins
o Poorer wetting
o Reliability Issues
o Thermomechanical fatigue at elevated temperatures
o Mechanical shock
o Vibration uncertain
o Sn with high levels of noble metals (Ag, Au) can have embrittlement issues
Alloy
Solidus
(ºC)
Liquidus
(ºC)
Sn(1-5)Ag(0.5-0.9)Cu 217 - 224
…Sn3.8Ag0.7Cu
…Sn3.0Ag0.5Cu
…Sn1.0Ag0.5Cu
Sn0.7Cu+(Ni, Co, etc.) 227
Sn(3-5)Ag 221
Sn(2-4)Ag(3-8)Bi 191-216
Sn10Ag 221 295
Sn3Cu 227 300
Sn10Au 217 217
Sn5Sb 235 240
12
Ductile-to-Brittle Transition
P. Ratchev, IMEC
13
Tin-antimony solder (95% tin)
o Standard Pb-free plumbing solder
o Good electrical properties of any common solder alloy.
o High strength at temperatures up to 300°F (150C)
o Good wettability
o Not recommended for use on aluminum, zinc, or galvanized steel
o Have similar characteristics to tin-silver alloys
o Not widely used
o When added to tin-based solders, antimony forms intermetallic structures with other materials, such as silver and copper, which adds to the strength of the alloy.
o Some concerns about Sb > 6%
o Antimony improves strength and does not affect wettability or flow characteristics.
o Antimony slows and reduces the growth of intermetallics with copper and other base metals when forming electrical interconnects
o Joint-clearance recommendations are the same as tin-lead solders.
o Does not react with tin, so it prevents tin pest (cold issue)
15
Constituents of Pb-Free Alloys
o Ag
o Improves strength through
SnAg intermetallics
o Conc. > 2% can reduce
mech. shock performance
o Conc. > 4% can cause
embrittlement
o Adequate supply but costly
o Cu
o Reduces melting point
o Retards dissolution rate
o In
o Can be susceptible to corrosion
o Expensive
o Best in low humidity conditions, or if it is conformally coated.
o Bi
o Reduces melting point
o By-product of lead mining
o Has embrittlement problems.
o Also a poor conductor, both thermally and electrically.
16
Quaternary ‘Pb-Free’ Alloys
o Considered too complex
Alloy Solidus (ºC) Liquidus (ºC)
Sn(2-4)Ag(0.5-0.9)Cu(1-3)Bi 207 221
SnAgCuSb
SnAgCuIn
Sn(2-4)Ag(4-8)In(0.5-2)Bi 197 215
SnAg2.5Cu0.8Sb0.5 (Castin) 217 225
SnCu2.0Sb0.8Ag0.2 219 235
17
Au-Based Systems (Hard-Solders)
o Well known in industry
o Opto-electronics
o Die attach
o Lid seal
o High modulus
o Creep resistance
o Corrosion resistant
o Disadvantages
o Requires reflow temp. of 320C and inert gas; may require pressure
o Cost
o Brittle
o Thermal and electrical conductivities are not optimum
o Other failure mechanisms (e.g., spalling)
Alloy Solidus (ºC) Liquidus (ºC)
Au12Ge 356 356
Au3.2Si 363 363
Sn80Au 280 280
M. Ishikawa, et. al., “Application of GoldTin
Solder Paste for Fine Parts and Devices,”
55th ECTC, June 2005, pp. 701 - 709
18
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Finally….
o Zinc alloys
o Provides minimal improvement in melt temperature
o Concerns with corrosion
o Has oxidation problems and also causes solder to become brittle. This oxidation problem creates an issue with existing automatic soldering equipment.
o Cadmium alloys
o Also banned by RoHS
o 100% Bismuth
o Melts at 271C
o Why is it bad?
o By-product of lead mining
o Has embrittlement problems.
o Also a poorer conductor, both thermally and electrically.
22
Alternative Paths Forward
o High temperature solders can survive temperatures
exceeding 150C
o Majority of electronic components cannot survive process
temperatures above 260C (at least not guaranteed!)
o Problem: Most alloys that can be used above 150C
require melting temperatures above 260C
o Solutions
o Limit temperature rise to the area of the interconnect
o Reduce the process temperatures (but not the melt temperature)
o Use something other than solder
23
Occam (Verdant Technologies)
o No solder or PCB required,
http://www.verdantelectronics.com/
o Announced in July 2007
o New test vehicles and Occam Prize planned for 2012
o Based on the HDI process developed by GE; but for circuit
assemblies
o Potential advantages
o Creates Cu-Cu interconnection at room temperature
o Melting temperature: >1000C
24
o Underlying idea is to build electronic assemblies without
solder
o Building the assemblies in “reverse order”.
o Place the components onto a temporary or permanent
carrier
o Affix them in place using a suitable encapsulant or carrier
and sealant
o Build up the circuits on top of the assembly.
o Net result would be a solder alloy free electronic (SAFE)
assembly that would be a virtually all Cu interconnection
system.
Occam Process Overview
25
Occam Process
o Component placement
o Same as pick-and-place
o Requires a ‘sticky’ substrate
o No self-alignment
o Single-sided resin coated copper?
o Encapsulation
o No rework or repair
26
Occam Process (cont.)
o Microvia fabrication o Laser drill
o Fill and/or Plate
o Laminate
o Repeat
27
Occam (Additional Thoughts)
o Requires copper-to-copper bonding o Sn-plating, Ni-plating, Alloy 42 leadframe could be problematic
o Scrap rates could be high
o Through-put could be limited o CO2 laser systems: 20,000 vias per minute
o UV laser systems: 4,000 vias per minute
o Cost difficult to assess o Microvias can be more
o Potential significant savings in board layers and real estate
o Merger of board and assembly processes may provide some cost savings – 1 shop process
M. Kauf, “Microvia Formation: Technology and Cost Comparison,” CircuiTree, January 30, 2002
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Adhera Technologies, www.adheratech.com
o Dopes standard solder materials with rare-earth elements
(Lutetium [Lu])
o Creates intermetallic phases that react with oxygen
o Phases chemically attack surface oxide
o Allows for bonding to glass and ceramic
o Enhances wetting behavior (no fluxes?)
o Actual composition difficult to determine
o Claims ability to tailor formulation
29
Adhera Technologies (cont.)
Stock Product
MP (ºC)
CTE (ppm/C)
Tensile Strength (ksi)
Comments
AS-1L ~220 21 38 Premium solder, high strength, high creep resistance, optical applications
AS-2LC ~220 40 40 Copper containing AS-1L, High strength, high creep resistance, electrical applications
AS-3EC ~220 39 40
Regular strength, general and low-cost applications,
high creep resistance, similar to SAC solders
AS-4IE ~118 24 12
Low-melting point, general applications with low temperature
tolerances.
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o Adhera's active solders combine base metals with rare-
earth elements in a patented formulation to create
nanodisperse intermetallic oxygen-scavenging
phases(labeled "A" in the figure).
Adhera, www.adheratech.com
31
Nanosilver Paste
o Consists of nanosized particles of silver combined with standard paste constituents
o Increase in surface energy drives sintering process (not soldering)
o Processing temperature of 275C
o Slightly above peak temperature of 260C for most components
o Well below process temperatures of standard hard solders
o High electrical and thermal conductivities
o Caveats
o Surfaces must be plated in silver or gold
o Recommended for devices less than 5mm x 5mm
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Nanosilver (cont.)
o Developed under a US Navy ManTech program
o First announced by Guo-Quan Lu of Virginia Tech (gqlu@vt.edu)
o 2004 to 2007
o Licensed to NBE Tech, LLC
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o http://www.nbetech.com/
o Product Description: Thick paste of nano-sized silver powder in an organic binder formulation.
o N-series: for bonding chips less than 3 mm x 3 mm without pressure at bondline thickness of 10 μm to 15 μm.
o K-series: for bonding large chips with modest pressure of less than 5 MPa or 730 psi at bondline thickness from 10 μm to 75 μm.
o Key Features
o Uniform dispersion for screen/stencil printing or dispensing
o Low sintering temperature
o Excellent sintered properties
o RoHS compliant
NBE Tech Nanosilver
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NBE Tech Nanosilver Pastes
Targeted at joining semiconductor chips for high-performance, high-reliability, and high junction-temperature applications
Power electronics, automotive electronics, concentrated photovoltaics, high-power light-emitting diodes (LEDs) or high-power laser diodes, and high-power, compact communication systems.
35
Transient Liquid Phase Bonding
o Similar, but less extreme example of process temperatures
less than melt temperatures
o Can be used with the Sn5Sb system
o Takes advantage of phase diagram behavior
o One constituent has a lower melting temperature than the
combined alloy
o E.g., Sn is 232C; Sn10Sb is 252C
o When the liquid Sn spreads around the solid Sb particles, in-situ
alloying between the Sn and Sb will take place
o Can be done as foils, thin films, or mixed powders
37
Indium NanoFoil and Nanobond, http://www.indium.com/nanofoil/
o What is NanoFoil?
o New class of nano-engineered material.
o Fabricated by vapor-depositing thousands of alternating nanoscale layers of Aluminum (Al) and Nickel (Ni).
o When activated by a small pulse of local energy from electrical, optical or thermal sources, the foil reacts to precisely deliver localized heat up to temperatures of 1500°C in fractions (thousandths) of a second.
38
NanoFoil, http://www.indium.com/nanofoil/
o Rapid, controlled, locally-applied heat source
o Instantaneous, flux-free soldering and brazing at room temperature
o Suitable for use with high-temperature solders or brazes
o Enables high-strength bonds between most combinations of materials
o Composition of foils and the thickness of layers can control temperatures and total energies of these reactions
o Soldering or brazing of temperature-sensitive electronics components or assemblies.
39
NanoBond
o Indium also provides a NanoBond technology
o Delivers a small pulse of localized energy
o Provides the necessary amount of heat and energy to reflow
solder or braze
o Potentially allows for melting of other alloys or
configurations in a very small space
o Potential problems
o Very small time scale can prevent intermetallic formation
40
NTP-1 (Btech), http://www.btechcorp.com/ntp1.html
o Highly electrically and thermally conductive Z-axis film adhesives.
o Very high conductivity fibers run through thickness of a film adhesive with precision orientation
o Continuous path avoids particle-to-particle contact problem of filled adhesives
o Wide range of fibers and thermoplastic matrices
o 8 and 4 micron diameter nickel fibers
o Up to 20 million fibers/in2
o Fibers tilt slightly to allow consolidation of bond line during cure
o Hot melt thermoplastics: polyamide, polypropylene, etc.
o Instant “cure” hot melt thermoplastic
o 110°C to 210°C bonding temperature options
o 80°C to 160°C continuous operating capability
41
B-Tech Tp Series Options
o Medium pitch density.…NTP-1
o uncoated pure nickel fibers
o continuous process, <25% cost of high pitch version
o being qualified for a variety of applications including:
plastic solar panel Z-axis interconnect, low cost microwave
PCBs, large area lead-free solder, and PET substrate circuit
lamination.
o High pitch density….TP-1
o heat treat Ni fibers in oxygen/argon to grow a ¼µ thick
green nickel oxide coating (NiO)
o >20 mega-ohm resistance on 30µ comb pattern
42
B-Tech Applications
o Fine pitch BGA and flip chip packages
o Flex circuit Z-axis interconnect
o Advanced fine pitch displays (11µ pitch)
o LCD assemblies
o replace current Z-axis adhesives
o RFID tags
43
B-Tech Conductive Fibers
o 40% Nickel Fiber Volume with Oxide Coating
44
B-Tech HM-2 Thermoplastic Thermally Conductive Adhesive
o 0.07 °C-sq. cm/W Z-axis thermal resistance
o -50°C to +160°C operating range
o Special high temperature thermoplastic for
automotive electronics
o 3000 thermal cycles
o 1000 hours total at +150°C
45
Advantages / Disadvantages
o Very high electrical and thermal conductivity
o Very compliant
o Reworkable
o Commercialized
o Requires pressure
o Approximately 25 psi
o Very sensitive to interfacial conductivity
46
High Temperature Polymer Matrices, RTP Engineering
o Continuous Use Temperature — Function of the thermal breakdown of the polymer. Difficult to increase by adjusting additives.
o Heat Deflection Temperature — Temperature at which a material will deflect a specified amount at a specified load. Good indicator of short term/low load thermal capabilities
o RTP Engineering Plastics (www.rtpcompany.com)
Resin Product
Description
HDT @
264 psi
Continuous
Use Temp
°F °C °F °C
Polyphenylene Sulfide (PPS) RTP 1305 500 260 425 218
Polyetheretherketone (PEEK) RTP 2205 HF 600 316 475 246
LCP RTP 3405-3 530 277 450 232
LCP RTP 3405-4 585 307 450 232
Polyphthalamide (PPA) RTP 4005 FR A HS 500 260 375 191
High Temperature Nylon (HTN) RTP 4405 FR 500 260 300 149
47
Paths Forward
o “Nano” technologies seem to be the most promising o Similar to technologies used for formulate semiconductors and
other devices
o Consider tweaking existing nano-technologies to reduce melt temperatures below 260C o Alloy development (single or binary composition)
o Occam process is interesting o Will require investment; some challenges
o Potential for high-temp anisotropic conductive films (ACF)
48
Contact Information
o Questions:
o Contact Cheryl Tulkoff, ctulkoff@dfrsolutions.com,
512-913-8624
o askdfr@dfrsolutions.com
o www.dfrsolutions.com
o Connect with me in LinkedIn as well!
49
Disclaimer & Confidentiality
o ANALYSIS INFORMATION
This report may include results obtained through analysis performed by DfR Solutions’ Sherlock software. This comprehensive tool is capable of identifying design flaws and predicting product performance. For more information, please contact sales@dfrsolutions.com.
o DISCLAIMER
DfR represents that a reasonable effort has been made to ensure the accuracy and reliability of the information within this report. However, DfR Solutions makes no warranty, both express and implied, concerning the content of this report, including, but not limited to the existence of any latent or patent defects, merchantability, and/or fitness for a particular use. DfR will not be liable for loss of use, revenue, profit, or any special, incidental, or consequential damages arising out of, connected with, or resulting from, the information presented within this report.
o CONFIDENTIALITY
The information contained in this document is considered to be proprietary to DfR Solutions and the appropriate recipient. Dissemination of this information, in whole or in part, without the prior written authorization of DfR Solutions, is strictly prohibited.
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Dr. Craig Hillman, CEO
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