1) The document presents research on developing novel leaded multilayer ceramic capacitors (MLCC) using transient liquid phase sintering (TLPS) materials for applications requiring reliability at temperatures over 175°C. 2) Two TLPS materials are characterized: Cu-Sn, which forms a metal matrix composite bond; and In-Ag, which forms a solid solution bond using a single metal paste diffusion process. 3) Testing shows both TLPS materials have higher maximum shear strength than common solders up to 300°C, indicating their potential as lead-free, high-temperature alternatives to solders for electronic interconnects.

1. Development and Characterization of Novel
Leaded High Temperature Multi-Layer Ceramic
Capacitors (MLCC) made using Transient Liquid
Phase Sintering (TLPS) Materials
Presented by: John Bultitude1
MS&T 15, Columbus, OH, USA, October 5, 2015
John McConnell1, Javaid Qazi1, Jim Magee1, Lonnie Jones1 Catherine
Shearer2, Ken Holcomb2 & Michael Matthews2
KEMET Corporation1 Ormet Circuits, Inc.2
2835 Kemet Way 6555 Nancy Ridge Drive, Suite 200
Simpsonville, SC 29681 San Diego, CA 92121
USA USA

2. Introduction
• Leaded MLCC can absorb larger CTE mismatches than surface
mounted components making them suitable for higher
temperature electronics that require reliable performance
operating at ≥ 175oC
• The processing temperatures for these electronic assemblies
have been increasing, in some cases ≥ 300oC, with components
required to survive multiple heating cycles
• These requirements surpass the capability of established
interconnect materials such as common solders and welds
• The performance novel Pb-free transient liquid phase sintering
(TLPS) materials at temperatures up to 300oC are compared to
these common interconnects

3. Presentation Outline
• High Temperature Electronics
– Trends by Market, Assembly Needs & Environmental Legislation
• Current Solder Capability
– Maximum Shear testing
• Transient Liquid Phase Sintering (TLPS)
– Comparison to solders
• Leaded MLCC TLPS Capacitor Trials
– TLPS Cu-Sn for Radial & Axial Leaded MLCC
– TLPS In-Ag for Stacked MLCC using a Single Metal Paste Diffusion
Process
– Microstructures & performance comparisons to solders
• Summary
• Conclusion & Future Work

4. Market Trends and Drivers for High
Temperature Electronics
350oC
325oC
300oC
250oC
200oC
150oC
275oC
225oC
175oC
125oC
2015 2016 2017 2018
Aerospace
Engine Control &
Monitoring Systems
Downhole
Automotive
Downhole
Deeper Wells
Automotive
Engine Control &
Monitoring Systems
Geothermal
Military
Power-Semi
Wide Band-gap Semi-
Conductors SiC, GaN
2019
Aerospace

5. Electronic Process & Operating Temperatures
AuGe or AuSi Solder $$$$$$$
Pb-Free RoHS 2
Compliant by July
22, 2016 -ELV
Process/OperatingTemp.
1950 1970 1990 2010 2020
Years
Hi Sn Solders,
60Sn40Pb,63Sn37Pb etc.
Hi Pb Solder alloys:
10Sn/88Pb/2Ag, 95Pb/5Sn
TLPS
160oC to > 800oC
RoHS Compliant
Interconnect
200oC
400oC
300oC
500oC
600oC
Lead Free solders
SAC Alloys, SnSb
Transient Liquid Phase
Sintering TLPS:
• Low Processing temp.
• High Re-melt temp.
• Pb-Free & RoHS Compliant
Potential Extension for > 85%
Pb-containing solders to 2021

6. Assembly Sequences vs Heat Cycles
Board Level Assembly
surface mount 1 reflow
SM Component
1st Solder
Reflow
Overmolding
Component
Assembly
1st Solder
Reflow
+
+ Leads
Board Level Assembly
components seeing 2nd reflow
2 Solder Reflows:
Lead + Board
+ Overmolding
275oC to 350oC
Module Sub-Assembly
2 Solder Reflows:
Lead + Board
Board Level Assembly components
seeing 3rd reflow
+
3 Solder Reflows:
Lead + Mod + Overmold + Board Assembly
IncreasingAssembly/Processing
Complexity

7. Shear Testing of Solders
Shear StressTesting
Ref. John Bultitude et al; Journal of Microelectronics & Electronic Packaging (2014), 11, 166-173
• Leads were attached to case size
4060 MLCC with selected solders
• Pull tests were performed at
temperatures up to 300oC
• The average maximum shear stress
at 0.1mm/sec was calculated for the
samples at different temperatures

8. Maximum Shear Stress @ High Temperatures
Selected Solders

9. What is TLPS?
– Low temperature reaction of low melting
point metal or alloy with a high melting
point metal or alloy to form a reacted
metal matrix
– Forms a metallurgical bond between 2
surfaces
How does it compare to solder?
– Bonding is specific to surface type &
TLPS used
– Applied as a paste or preform or plated
surface-to-surface
– Active fluxes to clean surfaces & bond
oxide/contaminants
– Polymeric binders retained in joint
– No rework is possible
– No wetting or fillet formation
– No solder ball formation
– TLPS has much higher re-melt >
600oC depending on the specific
alloys formed
TLPS Introduction & Solder Comparison

10. Maximum Temperature Capability
KEMET Hanging Weight Test Temperature of Joint Failure
Support Bar
Suspended
Parts
30 g
weights
• Box Kiln Temperature is increased
in steps until joint fails
• Solders fail close to melting points

11. Leaded MLCC TLPS Capacitor Trials
Radial 1206, 1µF, 50V
X8L
Axial 0805, 1nF &
1206, 47nF, 50V C0G
Cu –TLPS Cu-Sn – Cu Bonds
Conformal Coating
Ag – In(Ag) Single Metal
Paste Diffusion – Ag Bonds
Stack 2220, 0.1µF, 630V
C0G
US Patent Number 8,902,565 B2 & Pending Patents

12. TLPS Materials & Processes
1. TLPS Cu-Sn
– Metal Matrix Composite Bond
– Single Stage Sintering Process ~ 300oC peak temperature < 30 sec.
• Maximum Shear Strength Vs. Solders to 300oC (Overmolding Capability)
• Long term performance testing results @ 175oC (Operation)
• Microstructures and mechanical performance comparisons
2. TLPS In-Ag by Single Metal Paste Diffusion (SMPD)
– Solid Solution Bond
– Two stage SMPD process
• Process Development
• Microstructures & mechanical performance comparisons
• Maximum Shear Strength Vs. Solders to 300oC

13. Maximum Shear @ High Temperature
Radial MLCC TLPS Cu-Sn
Operating Temperature
Overmolding
Temperature

14. Maximum Shear Stress @ Temperature
Trends for Solders & TLPS Cu-Sn
R2 values for solders all > 0.96

15. Temperature & Shear Capability for Solders
& TLPS Cu-Sn
Interconnect Melting Point
(oC)
Zero Shear Intercept
Temperature (oC)
10Sn/88Pb/2Ag Solder 290 299
93.5Pb/5Sn/1.5Ag Solder 305 360
91.5Sn/8.5Sb Solder 240 269
SAC 305 Solder 217 265
TLPS Cu-Sn ~ 660 352
• Zero Shear for all solders is above their melting points
• Zero Shear for TLPS Cu-Sn is below the melting point so
useful range is at higher temperatures > 300oC

16. TLPS Cu-Sn Microstructure Vs. Solder
• Microstructure consists of copper in
copper-tin, a Metal Matrix Composite
*CuSn Intermetallics formed at SAC solder interface
*Ref. Catherine Shearer et al; IMAPs 2015; paper submitted
• Growth of Cu-Sn intermetallics
associated joint embrittlement are
of great concern with respect to
joint robustness
TLPS Cu-Sn SAC 305 Solder

17. TLPS Cu-Sn Extended Testing
• Axial Samples were tested as
follows:
• No failures in TLPS
* Failure at 2000hrs cycling was
due to fracture of MLCC
• 0805 parts were sheared before
and after these tests:
• Cycling decreases maximum
shear stress by ~ 40% but this
remains acceptable
Ref. John McConnell et al; IMAPs 2015; paper submitted
Test 1nF 47nF
High Temp. Storage 175oC Air
2000 hours
0/20 0/20
Load Humidity 85oC/85%RH 50V
2000 hours
0/20 0/20
Thermal Cycling -40 to 175oC
2000 cycles (30oC/min. ramp; 30
min. dwell) - Mounted
1/20* 0/20

18. TLPS Cu-Sn Microstructure
2000hrs @ 175oC
EDS Analysis of Atomic
Ratio’s:
• Ag/Sn ~ 3; Ag3Sn
• Cu/Sn ~ 1.2; Cu5Sn6
• Cu/Sn ~ 3; Cu3Sn
Cu
Cu

19. Cu-Sn and Ag-Sn Binary Phase Diagrams
http://www.metallurgy.nist.gov/phase/solder/agsn.html http://www.metallurgy.nist.gov/phase/solder/cusn.htm

20. TLPS Cu-Sn Shear Test Failures
2000hrs @ 175oC
In sheared samples
micro-cracks terminate
at the Cu spheres in
the Metal Matrix
Composite

21. TLPS Cu-Sn Shear Test Failures
2000hrs @ 175oC
Fractures meander
through the Metal
Matrix Composite

22. TLPS In-Ag
• Review our development of TLPS bonding using In-Ag for
stacked MLCC with no conformal coatings
• Initial tests were run on forming bonds by diffusion between
plated metal surfaces but the surfaces of leads and MLCC
are not planar making it difficult to form a large contact area
• For this reason we developed a Single Metal Paste
Diffusion (SMPD) process

23. Single Metal Paste Diffusion (SMPD)
Process
Ag Lead
Ag MLCC
Indium
Paste
Initial Bond Formation
• Low Pressure
• 250-350oC/30seconds
• N2 atmosphere
Ag Lead
Ag MLCC
In
Ag
Ag
InAg
Diffusion
• 200-300oC
• N2 atmosphere
Low Ag 500X
High Ag 1000X
Low Ag
500X
48hrs
200oC
High Ag
1000X
120hrs
200oC
US Patent Number 8,902,565 B2 & Pending Patents

24. Peel Strength Vs. Diffusion Time

25. TLPS In-Ag Microstructures
High Ag
• The SMPD process results in
an In-Ag Solid Solution Bond

26. In-Ag Binary Phase Diagram
Ref. Z. Moser et al; Journal of Electronic Materials (2001), Volume 30, Issue 9, 1120-1128
> Hot Peel Strength

27. Maximum Shear Stress @ Temperature
Trends for Solders & TLPS Cu-Sn & In-Ag

28. Temperature Capability & Shear Capability
Trends for Solders & TLPS In-Ag
Interconnect Melting
Point (oC)
Zero Shear Intercept
Temperature (oC)
10Sn/88Pb/2Ag Solder 290 299
93.5Pb/5Sn/1.5Ag Solder 305 360
91.5Sn/8.5Sb Solder 240 269
SAC 305 Solder 217 265
TLPS Cu-Sn ~ 660 352
TLPS In-Ag (High Ag SMPD Process) ~ 780 355
• Zero Shear calculation is based on poor fit for TLPS In-Ag
• At 300oC Maximum Shear for TLPS In-Ag is 2 X higher
than TLPS Cu-Sn
• Further refinement of our Single Metal Paste Diffusion
(SMPD) process is underway to improve the performance of
TLPS In-Ag at temperatures > 200oC

29. Summary
• A CuSn based TLPS has been used to manufacture Radial
& Axial Leaded MLCC with
– Maximum Shear Stress > Pb-based solders @ 300oC
– No TLPS failures through 175oC storage, cycling & biased humidity
• On shear testing micro-cracks in the Metal Matrix
Composite form and terminate at Cu spheres with fractures
meandering through the TLPS
• A Single Metal Paste Diffusion Process has been developed
and used in MLCC stacks with
– Solid Solution bonds of In-Ag
– High peel strengths @ 200oC
– Maximum Shear Stress > Pb-based solders @ 300oC & also higher
than for TLPS Cu-Sn

30. Conclusion & Future Work
• TLPS interconnects appears to be a suitable alternative to
high-Pb solders for leaded MLCC
• More extensive work is underway to
– Refine & scale-up the lead attachment processes
– Test at higher temperatures ≥ 200oC for longer times
– Evaluate cycling to higher temperatures
– Test mechanical shock performance

31. Acknowledgements
• Thanks to our technicians Garry Renner, Jeff Bell and Jeff
Murrell for their help supporting these developments

32. More Information
• Available at:
https://ec.kemet.com/tlps
www.ormetcircuits.com
• ‘High temperature capacitors and transient liquid phase
interconnects for Pb-solder replacement’ review in Journal
of Materials Science: Materials in Electronics