ELECTRONIC PACKAGING,
INTERCONNECTION AND ASSEMBLY PROGRAM
Today's U.S.
microelectronics and supporting infrastructure industries
are in fierce international competition to design and
produce new smaller, lighter, faster, more functional
electronics products more quickly and economically than
ever before.
Recognizing this trend, in 1994 the NIST Materials
Science and Engineering Laboratory (MSEL) began working
very closely with the U.S. semiconductor packaging,
electronic interconnection, assembly, and materials
supply industries. These earlier efforts led to the
development of an interdivisional MSEL program committed
to addressing industry=s
most pressing materials measurement and standards issues
central to the development and utilization of advanced
materials and material processes within new product
technologies, as outlined within leading industry
roadmaps1. The vision that accompanies this
program - to be the key resource within the Federal
Government for materials metrology development for
commercial microelectronics manufacturing - may be
realized through the following objectives:
- develop and deliver standard measurements and
data
- develop and apply in situ measurements on
materials and material assemblies having
micrometer- and submicrometer-scale dimensions
- quantify and record the divergence of material
properties from their bulk values as dimensions
are reduced and interfaces are approached
- develop fundamental understanding of materials
needed for future packaging, interconnection and
assembly schemes
With these objectives in mind, the program presently
consists of nearly twenty separate projects that examine
key materials-related issues, such as: electrical,
thermal, and mechanical characteristics of polymer and
metal thin films; solders, solderability and solder joint
design2; interfaces and adhesion;
electromigration and stress voidage; and built up stress
and moisture in plastic packages. These projects are
always conducted in concert with partners from industrial
consortia, individual companies, academia, and other
government agencies. The program is strongly coupled with
other microelectronics programs within government and
industry, including the National Semiconductor Metrology
Program (NSMP)3. The NSMP is a national
resource responsible for the development and
dissemination of new semiconductor measurement
technology.
More information about this program, and other NIST
activities in electronic packaging, interconnection and
assembly, is contained in Electronics Packaging,
Interconnection and Assembly at NIST: Guide and Resources,
NISTIR 5817
(http://www.msel.nist.gov/epia1996/contents.htm). Copies
may be obtained by contacting Michael Schen at (301)
975-6741 or michael.schen@nist.gov.
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1 National Technology Roadmap for
Semiconductors, Semiconductor Industry Association,
San Jose, CA, 1994, 1997 (in draft); National
Technology Roadmap for Electronic Interconnections,
Institute for Interconnecting and Packaging Electronic
Circuits, Lincolnwood, IL, 1995, 1997 (in draft); National
Electronics Manufacturing Technology Roadmap,
National Electronics Manufacturing Initiative, Inc.,
Herndon, VA, 1996.
2http://www.ctcms.nist.gov/programs/solder
3http://www.eeel.nist.gov/810.01/index.html
Significant Accomplishments
- For dielectric measurements, a coaxial sample
holder has been designed and tested and
measurement protocols instituted which eliminate
discrepancies in the overlap regions of frequency
in the several different instruments required to
cover the range from DC to 1 GHz. The new holder
reduces the relative measurement error in
capacitance and loss at 30 MHz from 8% using a
conventional four terminal holder to 0.1%. The
same configuration can be used at frequencies up
to 1 GHz where the relative uncertainty is about
1%. These techniques will allow the accurate
measurement of dielectric constant and loss of
thin film materials being evaluated for
interlayer dielectrics in the microelectronics
industry.
- Density profile and coefficient of thermal
expansion (CTE) of ultra-thin (~100 nm) spin-on
glass films have been determined by x-ray
reflectivity and reported in collaboration with
Dow-Corning Corp. Spin-on glass film is a primary
candidate for interlayer dielectrics in future
multi-level chips. Density profile and CTE are
critical data needed for chip design and are not
accessible with any other conventional
measurement techniques.
- A three terminal capacitance cell has been
designed and constructed of nichrome-coated fused
quartz electrodes that is capable of measuring
the out-of-plane coefficient of thermal expansion
of films as thin as 5 :m with a standard
uncertainty of 0.1% over a 100 /C interval
for polymeric materials whose properties are
sufficiently stable. This measurement technique
is expected to supplement the standard test
method for coefficient of thermal expansion which
is inadequate for providing reliable data on the
thin polymer films encountered in the design of
flexible circuits and microelectronic packaging.
- A new technique using twin neutron reflectivity
has been developed which enables the
determination of the density of thin films on
many substrates including silicon wafers with a
relative uncertainty of "1%.
Density of thin films, especially in the
ultra-thin range (#100
nm), provides important insights about the
structure of such films that has not been
previously determined with an accuracy of "1%.
- using twin neutron reflectivity, the density of
polystyrene thin films (10 to 100 nm thick) was
found not to differ significantly from that of
the bulk state. This finding is in contrast to a
commonly held notion of thin film density
depending on the type of substrate and film
thickness. Density is an important parameter
defining the structure of ultra-thin polymer
films.
- Neutron reflectometry measurements confirm that
polymer diffusion is impeded in an interfacial
region of thickness equal to about 3 radii of
gyration of the polymer away from a native oxide
silicon surface. The interaction range between
polymer chains and solid substrates is critical
to our understanding of many technically
important issues such as adhesion and
lubrication.
- The thermal pulse instrumentation for measuring
charge and/or polarization distribution and
thermal diffusivity of thin polymer films as well
as the heat transfer coefficient between film and
substrate has been improved so that films as thin
as 1 :m can
be measured with a depth resolution of 10 nm.
Thermal property data on thin films and
interfaces are required for the accurate design
for thermal management of the heat generated by
next generation integrated circuits.
- Demonstrated that the modulus and in-plane
coefficient of thermal expansion of spin-on
polymer films can be deduced from measurements of
the residual stress between the film and two
different substrates using an instrument designed
for measuring wafer bending. These data are
required for the accurate modeling of reliability
of packaged integrated circuits when subjected to
thermal cycling.
- In April 1997, SEMATECH, the Semiconductor
Research Corporation, and NIST conducted a
workshop on Interfaces and Adhesion in
Electronic Packaging and Assembly involving
experts from industry, academia and government.
The workshop explored new scientific
opportunities for enhancing the understanding and
robustness of material interfaces in
semiconductor devices. As the size of
microelectronic devices shrink, and their
complexities increase, industry has identified
material Ainterfaces
and adhesion@
as a critical area where substantial advancements
within the semiconductor industry are needed.
- In October 1996, the U.S. Air Force Rome
Laboratory and NIST sponsored the 6th
International Conference on Moisture in
Microelectronics at NIST=s
Laboratories in Gaithersburg, MD. Drawing over
ninety individuals from industry, academia and
government, this workshop was held to allow
researchers and engineers, in the
microelectronics industry, to exchange new
insights and knowledge on how moisture impacts
the performance and reliability of today=s
microelectronic products and packaging materials.
Moisture is universally seen as the single
largest environmental factor which threatens the
manufacturability and reliability of electronic
packages and interconnects.
Improved Measurement Technique for Hydrothermal
Expansion of Polymer Thin Films
F. I. Mopsik, C. Snyder and G. T. Davis
Objectives
The objectives are: i. Determine accuracy and
precision of NIST-designed capacitor cell technique for
measuring out-of-plane expansion of thin polymer films. ii.
Investigate the dimensional stability of electronics
packaging materials with temperature and humidity
changes. iii. Work with standards-setting bodies
to introduce NIST metrology as a new standard test
method.
Technical Description
Measurements will be made on a set of
well-characterized materials to evaluate the use of a
precision capacitance gauge for measuring small
dimensional changes in thin films. Studies will be made
using this gauge to measure thermal expansion properties
of polymer materials used in microelectronics as well as
their response to changes in humidity.
External Collaborations
Dr. Edward Shaffer of Dow Chemical Co. collaborates by
preparing and supplying thin films of polymers of
interest to his company which have been measured by other
techniques. He will also prepare spin coated films of
well-characterized polymers for studies of constrained
films.
Dr. Luu Nguyen of National Semiconductor Corp.
collaborates by supplying plaques of molding compound
used in the measurement of expansion due to absorption of
moisture.
Planned Outcomes
- Improved test method for expansion of thin films
- Reliable data on the expansion behavior of
electronic packaging materials with variations in
temperature and humidity
Accomplishments
- A three terminal capacitance cell has been
designed and constructed of nichrome-coated fused
quartz electrodes that is capable of measuring
the out-of-plane coefficient of thermal expansion
of films as thin as 5 :m with a relative
standard uncertainty of 0.1% over a 100 /C interval
for polymeric materials whose properties are
sufficiently stable. This measurement
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