1. Reliable Micro Joining
For applications with long lifetime expectations
Jan Eite Bullema
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Jan Eite Bullema
Reliable Micro Joining
Content
What are micro interconnections?
Reliable electrical micro interconnections with long lifetime expectations?
Solder micro interconnects and common failure mechanisms
Adhesive micro interconnect and common failure mechanisms
How to achieve durability in a micro interconnect
Innovative micro interconnection technology
Conclusion

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Micro Joining
Micro joining is the expression used for the joining of two metals were
one of the metals is thinner than 0.5 millimetre (metal sheets) or a cross
section smaller than 1 millimetre (wire)
Examples of technologies for micro joining are: welding, adhesive
bonding, ultrasonic bonding, soldering and brazing.
In electronic manufacturing mainly wire bonding, soldering and
adhesive bonding are used
J.E. Bullema ‘Optimaliseren van processen voor microverbinden’, VM 116 , ISBN 9789075740127
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Quality, Reliability, Durability
Meaning Quality Reliability Durability
Concept Conformance Failure Rate Product Life
to Specification
Recommended Per cent Per cent / Year Year or
Units or ppm Per cent / Hour Hour
Probability Density Normal Exponential Weibull
Function
Dongsu Ryu ‘Novel Concepts for Reliability Technology’, Micro Electronics Reliability 45, 2005, 611-622

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Example: Durability of a Space System
The Voyager 2 was launched on August 20, 1977. Its initial purpose
was to explore Jupiter and Saturn, with an operational life of 5 years
Currently, after 35 years the Voyager 2 is about 15.000.000.000 km
from the earth and the electronics still function satisfactory
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Content
What are micro interconnections?
Reliable micro interconnections with long lifetime expectations?
Solder micro interconnects and common failure mechanisms
Adhesive micro interconnect and common failure mechanisms
How to achieve durability in a micro interconnect
Conclusion

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Durability of Silicon Solar Modules
The European Photovoltaic Industry Association (EPIA) has set a target
in their solar energy roadmap for silicon solar modules from the current
20 years useful life to 30 year in the near future.
This increase in lifetime is expected to reduce the cost of solar energy
from 0,18 Euro / kWh to 0,12 Euro / kWh
European Photovoltaic Industry Association, ‘On the road to competitiveness, Solar Photovoltaics’, September 2011
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Reliability Issues in PhotoVoltaic Panels
First Solar: 232.000 Panels need Repair
The panels, made between
October 2008 and June 2009,
“may over time develop a loose
cord-plate attachment,”

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Durability of LED Systems
Life time of a LED System has to be 25 000 – 50 000 hrs.
Gielen et al, Development of an intelligent integrated LED system-in-package, EPMC 2011
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Reliable Micro Joining
Content
What are micro interconnections?
Reliable electrical micro interconnections with long lifetime expectations?
Solder micro interconnects and common failure mechanisms
Adhesive micro interconnect and common failure mechanisms
How to achieve durability in a micro interconnect
Innovative micro interconnection technology
Conclusion

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Solder Joint Reliability
Solder joint reliability is the ability of solder joints to function under given
conditions and to remain in conformance to both mechanical and
electrical specifications for a specified period of time (without failing
within the intended operating time).
Grossman et al., The ELFNET Book on Failure Mechanisms, Testing Methods, and Quality Issues of Lead-Free
Solder Interconnects, , ISBN 978-0-85729-235-3, Springer 2012
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Failure Mechanisms in Solder
and Related Stress Environments
Failure Mech. Stress Environment Description
Fatigue Temperature Cycling Initiates with micro crack
Creep Permanent Load Global Plastic Deformation
Corrosion Galvanic Pair Different Potential
Brittle Fracture Drop or Shock Intermetallic Layer Solder
Grossman et al., The ELFNET Book on Failure Mechanisms, Testing Methods, and Quality Issues of Lead-Free
Solder Interconnects, , ISBN 978-0-85729-235-3, Springer 2012

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Micro Structure of a Solder Joint
Cu | SnAgCu interface annealed at 250C for 1 h in order to detect
the Cu3Sn layer in between the Cu pad and the Cu6Sn5
Grossman et al., The ELFNET Book on Failure Mechanisms, Testing Methods, and Quality Issues of Lead-Free
Solder Interconnects, , ISBN 978-0-85729-235-3, Springer 2012
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Brittle fracture
Cracks propagated inside the Cu6Sn5 intermetallic compound layer
Grossman et al., The ELFNET Book on Failure Mechanisms, Testing Methods, and Quality Issues of Lead-Free
Solder Interconnects, ISBN 978-0-85729-235-3, Springer 2012

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Component Interconnections
in Temperature Cycling
T0 T0 T
Component
Solder
Substrate
Grossman et al., The ELFNET Book on Failure Mechanisms, Testing Methods, and Quality Issues of Lead-Free
Solder Interconnects, ISBN 978-0-85729-235-3, Springer 2012
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Development of Fatigue Failure
Grain Micro Micro Macro
Growth Voids Cracks Cracks
Crack Propagation
Crack Initiation
time
Grossman et al., The ELFNET Book on Failure Mechanisms, Testing Methods, and Quality Issues of Lead-Free
Solder Interconnects, ISBN 978-0-85729-235-3, Springer 2012

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Fatigue Failure
Cross section of thermally cycled SnAgCu solder joint
Grossman et al., The ELFNET Book on Failure Mechanisms, Testing Methods, and Quality Issues of Lead-Free
Solder Interconnects, ISBN 978-0-85729-235-3, Springer 2012
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Example: Realisation of ESIP LED system
Bullema et al, ‘’Combination of a Bayesian Network and FEM models to predict Reliability of LED systems’ ESTC 2012

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Reliable Micro Joining
Example: Design FEM of ESIP LED system
Example of a very compact design of a LED system,
Consequence are higher temperatures
Creep of solder interconnect chosen as failure mechanism
Gielen et al, Development of an intelligent integrated LED system-in-package, EPMC 2011
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Example: Calculation of a LED system
Gielen et al, Development of an intelligent integrated LED system-in-package, EPMC 2011

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Predicted Survival Rate R(t) of a LED System
Calculation R(t) for Uncooled and Cooled (T = T Uncooled - 20 C) Design
Uncooled ESIP
Caveat: Presented Prediction based upon assumed FIT not on test data
Bullema et al, ‘’Combination of a Bayesian Network and FEM models to predict Reliability of LED systems’ ESTC 2012
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Titel van de presentatie
Example: FEM Model of CSSL LED system
LV@22 C LV@45 C HV@22 C HV@45 C
Example of a retrofit Light Bulb type design of a LED system,
Challenge here again: Thermal Management
Creep of solder interconnect chosen as dominant failure mechanism
Bullema et al, ‘’Combination of a Bayesian Network and FEM models to predict Reliability of LED systems’ ESTC 2012

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Predicted Survival Rate R(t) of a LED System
ESIP with and
without heat pipe
Caveat: Presented Prediction based upon assumed FIT not on test data CSSL Design A, B
At Low and High Temp
Bullema et al, ‘’Combination of a Bayesian Network and FEM models to predict Reliability of LED systems’ ESTC 2012
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Content
What are micro interconnections?
Reliable electrical micro interconnections with long lifetime expectations?
Solder micro interconnects and common failure mechanisms
Adhesive micro interconnect and common failure mechanisms
How to achieve durability in a micro interconnect
Innovative micro interconnection technology
Conclusion

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Comparison Adhesive Micro Joining
versus Soldered Micro Joining
Characteristic Sn/Pb Solder ECA / ICA
Volume Resisitivity 15  / cm 350  / cm
Typical Junction R 10 - 15 mW < 25 mW
Thermal Conductivity 30 W / m.K 3,5W / m.K
Shear Strength 15 MPa 14 MPa
Finest Pitch 300 m 150 m
Processing Temp. 215 ºC < 150 ºC
Environmental Impact Negative Very Minor
Thermal Fatigue Yes Minimal
C.P. Wong, Nano-Bio- Electronic, Photonic and MEMS Packaging, Springer 2010, ISBN 9781441900395
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Conductive Adhesives
in Solar Panel Interconnections
Symbolic representation of the Microscopic picture showing silver
conducting mechanism of plated copper tab glued on silver
conductive epoxy adhesives. plated silicon solar cell (upper right
to lower left).
Nieuwenhof et al., Conductive Adhesives for Low Stress Solar ICell interconnections, IEEE 2002

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Conductive Adhesives in Solar Panel
Interconnections
soldering with iron
soldering with thermode
glued at 80°C
Stress on 80μm thin PhotoVoltaic cells interconnected to 70μm thick
copper tabs with different micro joining technologies.
Nieuwenhof et al., Conductive Adhesives for Low Stress Solar Cell interconnections, IEEE 2002
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Failure Mechanisms in Adhesives
and Related Stress Environments
Failure Mech. Stress Environment Description
Swelling Moisture Initiates with micro crack
Plasticization Moisture Depression of Tg
Conductivity Moisture Different Potential
Fracture Drop or Shock Loss of function
Johan Liu, Reliability of Micro Systems, Interconnects, Devices and Systems, Springer 2011 ISBN 978-1-4419-5759-7

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Content
What are micro interconnections?
Reliable electrical micro interconnections with long lifetime expectations?
Solder micro interconnects and common failure mechanisms
Adhesive micro interconnect and common failure mechanisms
How to achieve durability in a micro interconnect
Innovative micro interconnection technology
Conclusion
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Improve System Design
How to Improve the Interconnect Design
Analyse and Minimize Mechanical and Thermal Stress:
Matching of Coefficient of Thermal Expansion
Keep it Cool (at Room Temperature)
Analyse and Minimize Thermodynamic Stress:
Galvanic Series, Pourbaix Diagrams, Ellingham Diagrams
Prevent Moisture Ingress in adhesive interconnections

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Analyse and Minimize Stress Conditions
e.g. FEM Analysis of Thermal Stress
Minimize Dissipation, Cooling, Optimize thermal paths
Gielen et al, Development of an intelligent integrated LED system-in-package, EPMC 2011
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Content
What are micro interconnections?
Reliable electrical micro interconnections with long lifetime expectations?
Solder micro interconnects and common failure mechanisms
Adhesive micro interconnect and common failure mechanisms
How to achieve durability in a micro interconnect
Innovative micro interconnection technology
Conclusion

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Innovative Interconnection Technology
Innovative Technologies
Liquid Solder; Eutectic alloy of GaIn
Innolot Solder Alloy Alloy of Sn, Ag, Cu, Ni, Sb, Bi
Silver Sintering; Argomax, SKIN, Ablestick SP2000
Nano Copper Filled Adhesives Applied Nanotech
LIFT Laser Induced Forward Transfer
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Laser-Induced Forward Transfer
a technique for versatile micro-joining
possible deposits, depending on process parameters:
droplet splash pancake spray

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Laser-Induced Forward Transfer
Conductive copper lines
small lines
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Content
What are micro interconnections?
Reliable electrical micro interconnections with long lifetime expectations?
Solder micro interconnects and common failure mechanisms
Adhesive micro interconnect and common failure mechanisms
How to achieve durability in a micro interconnect
Conclusion

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Conclusions
It is possible to create system with enhanced life time by careful design
of interconnection technology, by
• Appropriate Material choice (e.g. CTE matching, intermetallics)
• Knowledge of Failure Mechanisms and Acceleration Mechanisms
• Analysis of Stress Conditions (e.g. Mechanical, Thermal, Chemical)
• Improve product designs based upon insight from advanced modelling
• Explore new innovative interconnection technologies
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Aknowledgements
This work is supported by the ENIAC JU and the national authorities
of the participating countries in the projects ESiP and CSSL.
Thanks to Robert Werkhoven, Jos Kunen, Monique van den
Nieuwenhof, Marc Hoppenbrouwers and Sander Gielen from TNO
for their valuable discussions and contributions for this presentation.