For the past five years, the CALCE EPSC has been conducting research
on health monitoring and prognostics for electronic systems. The
purpose is to provide advance warning of failure as a means to enhance
product sustainment, maintenance, reuse, and take-back.
CALCE’s strategies include (i) use of sensor technologies with
physics-of-failure analysis to assess real-time life consumption
monitoring of electronic systems; (ii) use of diagnostic built-in-test
(BIT) software-firmware systems to identify and locate faults that
incorporate error detection and correction circuits and self-checking
and self-verification circuits; (iii) use of in-situ semiconductor
prognostic monitors consisting of pre-calibrated cells (circuits) to
predict remaining life due to semiconductor faults, defects, and
failure mechanisms; and (iv) use of software modules (data collection,
simplification and damage accumulation and remaining life estimation)
to support environment and usage data collection that enables health
management.
CALCE has already conducted a remaining life assessment of the
space shuttle remote manipulator system electronics for NASA. We are
now conducting health and life assessment for the space shuttle rocket
booster electronics hardware.
CALCE’s methodologies have also been successfully demonstrated
for an electronic board operating in an automotive underhood
environment. In contrast to traditionally-used electronics reliability
prediction methods, the CALCE methodology was shown to effectively
predict remaining life.
Current research at the Center focuses on developing an
integrated hardware-software solution that can enable real-time health
and usage monitoring of electronic products in the application
environment. Software takes environmental and operational sensor data
as input, and processes it using data-reduction and cycle-counting
algorithms to predict the remaining life of the product using
appropriate stress-damage models.
CALCE’s vision for the future is to develop micro-programmable
modules that will enable health monitoring and prognostics of
electronics. In addition, CALCE is investigating biological systems and
health improvement monitoring methods to address conditions such as
diabetes.
For further information on these efforts, please contact Prof. M. Pecht or Dr. P. Rodgers at 301-405-5323.
back to top
CALCE EPSC has conducted a five-week training for eight quality and
reliability engineers from Samsung Electronics in Korea and a
three-week training for reliability and quality managers of Emerson
Network Power in China.
The training included a reliability short course covering
reliability concepts, probability distributions and statistics, design
for reliability, reliability prediction, part selection and management,
product qualification, accelerated testing, failure modes, mechanisms,
and effects analysis (FMMEA), failure/root cause analysis, derating,
screening and burn-in, and virtual qualification. Included were also
lectures on special reliability issues of interest to each company,
such as thermal effects on product reliability, electrostatic discharge
(ESD) failures in microelectronics, intermittent failure, electronic
product health/life consumption monitoring methodology, lead-free
solders and tin whiskers, reliability management, and thermal/vibration
analysis using calcePWA reliability software. Samsung Electronics has a
plan to continue training its engineers through CALCE industry courses.
Similar targeted training programs can be arranged for your organization.
For more information on the patent management software, contact
Prof. Michael Pecht.
back to top
The electronics industry is migrating to lead-free electronics, both
to comply with government legislation and to increase market share
through product differentiation. Considering that lead-based
electronics have been in use for over 50 years, the adoption of
lead-free technology represents a major change. The manufacturing of
lead-free electronic products involves assembling lead-free components
to lead-free printed circuit boards using lead-free solder alloys. Key
issues that are being addressed by academia and industry include
lead-free solder alloy selection, characterization of its properties
and behavior under various stress loading conditions, lead-free
manufacturing, logistics and intellectual property issues, and
lead-free assembly reliability assessment.
There are abundant data on the short-term durability (less
than 5 years) of lead-free solder joints under single loading
conditions. However, data on combined loading conditions and long-term
durability is scarce. The lead-free electronics will be deployed in
many products that serve markets where long-term reliability (greater
than 5 years) is a critical requirement. In many applications,
electronics will be subjected to long-term exposure to temperature
extremes (high and low), humidity, and combined thermomechanical
loading. Key long-term reliability issues should include unacceptable
growth of intermetallics at the solder joints due to high temperature
exposure, electrochemical degradation of electronics assemblies due to
exposure to humidity, formation of tin pest due to extended exposure to
low temperature and the effects of combined thermomechanical loading
conditions on the PCB assemblies. Thus the objectives of these studies
are as follows:
- Assess and compare lead-free technology against lead-based technology for long-term (5-30 year) reliability.
- Provide recommendations to reduce reliability risks to reach the long-term reliability goal of 5-30 years of operating life.
The key results expected are:
- failure mechanisms and modes in solder joint failures under
short-term vibration, temperature cycling, and combined temperature
cycling and vibration conditions
- long-term life of lead-free assemblies compared with that of lead-based assemblies
- life of lead-free solder joints (in comparison with Pb-based) under
the combined temperature cycling and vibration for several interacting
factors: high-volume lead-free assembly process; component types,
component finishes (matte Sn, Sn-Cu, and Sn-Bi), PCB pad finishes
(Immersion Ag, Immersion Sn, ENIG, and OSP with HASL as control)
- impact of long-term exposure of assemblies to low and high temperatures
- impact of PCB degradation due to high temperature lead-free
soldering and the lead-free solders (containing Ag) in causing
electrochemical migration and corrosion failures
Currently, seven companies, representing aerospace, military,
industrial, and telecommunication sectors, have joined this
collaborative effort. Companies interested in participating in the
studies should contact Prof. Michael Pecht at 301-405-5323, or Dr. Sanka Ganesan at 301-405-0765.
back to top
The CALCE Electronic Products and System Center is working with
Xerox to explore the potential of using some unique, high performance
carbon fiber composites (CFCs) as electronic interconnects. Various
configurations of these conductive plastics have already been shown to
provide advantages relating to high performance, low cost, and high
reliability in applications such as sliding contacts, switches, and
sensors.
The Center is evaluating the electrical and electromechanical
properties of the carbon fiber and metal-plated carbon fibers used to
make the composites. Preliminary results indicate that thin metal
layers on the base carbon fiber can effectively manage the electrical
resistivity into the desired range for interconnects. For example, a
1-mm thick nickel layer on a 7-8 mm commercial carbon fiber can produce
an effective resistivity of 10-4 W-cm. We
employed conventional soldering techniques to generate permanent
connections of carbon fiber-based materials to printed circuit boards
using both tin-lead and lead-free solders. The robustness and
reliability of these unique solder joints are being evaluated.
In addition, CFCs can be used to create temporary or separable
interconnects in the form of CFC-to-CFC or CFC-to-metal interfaces. We
are investigating the performance and properties of these unique
separable contacts by use of laser and heat-processed CFC surfaces,
which are paired with gold electrodes under tightly controlled
conditions. Contact resistances as a function of normal force are
characterized by using the CALCE Automated Contact Resistance Probe.
The contact resistance of a 1.6 mm diameter CFC rod mated to a
gold-plated surface was identified to fall in the range of 280 to 300 mW
at 50 grams normal force. Separable contacts of metalized CFCs to
various metal surfaces will also be studied. The early results are
suggesting that CFCs may some day be used as IC package-to-board and
board-to-board interconnects. please contact Dr. Ji Wu at 301-405-5901.
back to top
Six Sigma is a systematic, scientific, and information based
improvement process for processes such as manufacturing, design and
business. The implementation of Six Sigma results in auditable
financial benefits for an organization. The continued improvement
process consists of five steps in solving a problem or working on a
project: define, measure, analyze, improve, control (DMAIC).
The CALCE EPSC has developed tools for training organizations
interested in learning and applying Six Sigma tools for their
employees. Two CALCE research team members, Dr. Diganta Das, are Six
Sigma Black Belts and can help you design a tailored Six Sigma training
course for your organization.
On October 18, 2004, CALCE EPSC will hold a workshop on the
implementation of Six Sigma at the Greenbelt Marriott. For more
information, please contact Dr. Diganta Das at 301-405-5770.
back to top
Prognostics is the estimation of remaining life in terms that are
useful to the maintenance decision process. All prognostic health
management (PHM) approaches are essentially the extrapolation of trends
based on recent observations to estimate remaining life. It has been
previously pointed out (Engel et al, IEEE Aerospace Conference, 2000)
that the calculation of remaining life alone does not provide
sufficient information to form a decision or to determine corrective
action. Without accommodating the corresponding measures of the
uncertainty associated with the calculation, remaining life projections
have limited practical value. It is the accommodation of the
corresponding uncertainties that is at the heart of being able to
develop a business case for PHM.
CALCE EPSC has developed a model applicable to single LRUs
(line replaceable units) that enables the determination of when
scheduled maintenance makes business sense, and how to optimally
interpret prognostic health management damage accumulation or failure
precursor monitoring results for applications that are subject to a
combination of random failures and failures that have some determinism
associated with them. Optimal represents a combination of maximizing
availability and/or minimizing life-cycle cost. Specifically the model
is targeted at the following questions:
- How do we determine on an application-specific basis when the
reliability of electronics has become deterministic enough to warrant
the application of PHM-based scheduled maintenance concepts? Note, we
do not mean to imply that determinism in isolation is the criterion for
PHM vs. non-PHM solutions.
- Given that the forecasting ability of PHM is fraught with
uncertainties in the sensor data collected, the data reduction methods,
the models applied, the material parameters assumed in the models,
etc., how can PHM results be interpreted so as to provide value? This
boils down to determining optimal safety margins on life consumption
monitoring predictions and prognostic distances for health monitoring.
- How can a business case be constructed to show the usefulness of
health monitoring and/or life consumption monitoring for electronic
systems?
Previous PHM work on electronic systems has demonstrated
life-consumption monitoring for electronic systems. However, the
previous work has not addressed if (or how) an application’s life-cycle
cost can actually be reduced and/or operational availability increased
by using PHM. CALCE EPSC is currently working to extend the single LRU
decision model to multiple LRU systems.
To obtain further information on the decision support model for prognostic health management, please contact Dr. Peter Sandborn at 301-405-3167.
back to top
The rapid evolution of sensor technologies over the preceding twenty
years has been enabled by the commensurate evolution of integrated
circuits, micro-electromechanical systems, improved passive components,
software, communication protocols, and miniature power sources. The
development of advanced sensor technologies offers industry a great
many new commercial and technical opportunities. To help empower
industry to make correct product and technology investment choices, the
National Electronics Manufacturing Initiative (NEMI), in collaboration
with the CALCE EPSC, has initiated efforts to develop a sensors
technology roadmap. The CALCE EPSC team is leading the sensors
technology working group. The working group will analyze established
technological and manufacturing capabilities and compare these to
existing and anticipated sensor applications across multiple market
sectors, including transportation, health care, consumer electronics,
industrial and telecommunications infrastructure, defense, security,
and space. This process will highlight the gaps that represent
obstacles to fully realizing the benefits offered by advanced sensors
over the coming decade. These efforts will also incorporate an analysis
of the impact of disruptive technologies (carbon nanotubes,
micro-fluidics, distributed sensing) on capabilities for existing as
well as new applications.
Small embedded sensor technologies represent a major new
development for the 21st century, and will eventually become ubiquitous
in electronic and mechanical equipment. With integrated data
processing, memory, and communications functions, these devices will
radically alter our approach to activities as diverse as industrial
process engineering, equipment maintenance, military combat, and
surveillance. In parallel with our effort with NEMI, CALCE EPSC is
proceeding to develop capabilities for exploiting sensors in life-cycle
management and product health monitoring. In the field of reliability
engineering, embedded sensors will reduce the uncertainty associated
with scheduling of maintenance and replacement by providing a complete
history of environmental and operational loading conditions, as well as
performance history. When coupled with results of CALCE’s physics of
failure-based life cycle modeling, the use of embedded sensors will
allow improved accuracy and cost effectiveness in decisions concerning
product life-cycle management, leading to increased system availability
and reliability. Such features could alert users to potential damage
during operation, or even predict impending product failure. The
benefits of such an approach have already been amply demonstrated in
the marketplace by the self-monitoring analysis and reporting
technology (SMART) employed in disk drives. These embedded sensing
capabilities will also impact end-of-life decisions concerning
component recovery and reuse, especially when applied to take-back
scenarios, as described in an accompanying article in this newsletter
[see CALCE Investigates Product Take-back].
For further information on the sensor and MEMS efforts at the CALCE Electronic Products and Systems Center, please contact Dr. Michael Azarian at 301-405-8126, or Dr. Sanka Ganesan at 301-405-0765.
back to top
A CALCE EPSC survey of electronic component manufacturers indicates
that, due to low cost of tin and its compatibility with conventional
and lead-free solders, pure tin is the dominant Pb-free option for
terminal finish. A major concern related to the use of tin finishes is
the formation of tin whiskers, which can cause electrical short
failures of electronic hardware and has been associated with costly
losses of fielded systems.
Due to the unknown nature of tin whisker growth, some industry
segments, especially those who require longer product life and high
reliability, are interested in evaluating possible mitigation
strategies to retard tin whisker growth. The easiest and fastest
mitigation strategy to avoiding pure tin finishes appears to be less
possible for equipment manufacturers, since more than half of the
component suppliers have already adopted pure matte tin and this trend
is expected to continue.
CALCE EPSC has recently conducted a study evaluating the
effectiveness of heat treatment on tin-finished specimens in reducing
or eliminating tin whisker growth. Test specimens, including matte and
bright tin, plated over three different base metals (copper, brass, and
alloy 42) were subjected to three heat treatments, including annealing
and reflow at two different temperatures. Twenty-four specimens in each
category were commercially electroplated (200 micro inches thickness).
Electroplating parameters for matte and bright tin included the range
of current density (5~20A/cm2) and the plating bath
temperature (60~70ºC). A sulfuric acid bath was used for bright tin
plating. In order to determine the contamination level of plating,
detected contaminations include chloride: 0.074 ppm, bromide: 0.173
ppm, nitrite: 0.180 ppm, and sulphate: 0.074 ppm.
On average, the grain size of matte and bright tin used in
this experiment was found to be 4.6µm and 0.9µm respectively. Heat
treatments included annealing (approximately 1 week after plating at
150ºC for 1 hour) and two reflow profiles (only temperature exposure
without solder or flux). The first reflow profile was based on SnPb
solder with peak temperature of 220ºC. The second reflow profile was
based on a Pb-free solder with a peak temperature of 260ºC. Following
these heat treatments, specimens were split into three groups, with
some subjected to temperature cycling (-40 to 80ºC),
temperature/humidity exposure (60ºC/95%RH), or room ambient conditions.
Whisker growth is being monitored using an optical microscope and
environmental-scanning electron microscopy (E-SEM).
The result of this analysis indicated that whisker formation
may not necessarily be eliminated by the selected heat treatment
strategies. The test data indicated increase in maximum length and
density of whiskers over time. Matte tin-plated specimens induced fewer
and shorter whiskers, compared to bright tin-plated specimens. The
increase in whisker density observed in all cases after 7 months of
storage at room ambient indicates that the selected strategies are not
effective in retarding tin whisker formation.
To obtain more information regarding CALCE EPSC efforts related to tin whiskers, please contact Dr. Michael Osterman at 301-405-8023.
back to top
The European Directive on Waste from Electrical and Electronic
Equipment (WEEE) was adopted to promote recycling and recovery of
electronic equipment. This directive requires that European Union
member states enact national legislation placing financial
responsibility for “collection, treatment, reuse, recovery and
recycling of WEEE?on equipment producers. Some European countries,
including Belgium, Denmark, and the Netherlands, have already
introduced systems for take-back of electronic goods. In addition,
several major corporations, such as IBM, HP, and Apple Computer, have
proactively established take-back programs in Europe. HP estimates its
annual cost for take-back in Germany alone to be 10 to 30 M Euros. The
passage of take-back legislation across the EU will create the need for
fundamental and far-reaching changes within the electronics industry to
minimize the costs associated with compliance. This will include
changes to product design, manufacturing, distribution, life- cycle
management, and disposal.
CALCE EPSC has therefore initiated a program to study the
implications of the WEEE directive with the objective of providing
guidance to the electronics industry on measures for cost-effective
compliance. A team of CALCE research staff and graduate students has
identified a number of issues requiring further study that are in the
critical path to successful industry compliance with WEEE. These
include:
- Component Technology. Significant uncertainty remains regarding
optimal component selection criteria for recovery and reuse at low cost
and high reliability. Standardization across product lines will
simplify recovery, though effective health monitoring will be necessary
for decision-making regarding reuse vs. disposal upon recovery and
ensuring reliability of refurbished and remanufactured products. CALCE
EPSC has developed tools and expertise in health monitoring that can
help manufacturers minimize the risks associated with component reuse.
- Design for Disassembly. Due to the high levels of reuse or
recycling demanded by WEEE regulations, it is critical to understand
how to design and assemble products in order to facilitate disassembly
without sacrificing reliability. Special interconnect and assembly
features can make recovery easier, including customized embedded
devices. Modeling ease of disassembly for alternative designs and
recovery sequences favoring high-value components early in the process
will improve process efficiency.
- Supply Chain. Costs associated with collection,
transportation, and sorting of products are a significant fraction of
the overall costs associated with take-back. The reverse logistics
infrastructure in Europe is in an early state of development and will
be expanding over the coming years. A thorough capability study of this
infrastructure, along with the benefits of collective vs. independent
solutions, is needed.
- Legislative Requirements for Take-back. The EU WEEE directive
incorporates a number of exemptions, amendments, and product-specific
requirements. With 25 EU member states free to set more restrictive
regulations than those specified in the directive, and evolving
environmental legislation in the US and Asia, an effective program of
compliance must address the complete set of regulations across all
markets served.
For more information, contact Dr. Michael Azarian at 301-405-8126.
back to top
Increases in die heat flux and power dissipation, which are on the
exponential rise at all levels of electronic packaging, combined with
more stringent performance and reliability constraints in the future,
pose challenges that make thermal management a key enabling technology
in the development of microelectronic systems. Many IC packaging
failure mechanisms have been found to be dependent upon spatial
temperature gradients, temperature cycle magnitude, rate of temperature
change, rather than absolute temperature, while die circuit electrical
performance can be highly sensitive to operating temperature. While no
simple, generic relationship exists that relates electronics
reliability to these variables, it is accepted that temperature must be
controlled to meet both performance and reliability requirements.
Over the last 15 years, the CALCE EPSC has invested
considerable effort in the enhancement and characterization of both
conventional and advanced cooling technologies. To respond to the
industry’s current demand, two ongoing initiatives at the Center focus
on extending the limits of air-cooling and assessing the predictive
capability of computational fluids dynamics (CFD) codes for electronic
component operational temperature.
CFD Predictive Accuracy. The thermal design of today’s
electronic equipment relies significantly on the use of CFD software
for the prediction of electronics thermal performance. In the
early-to-intermediate product design phase, CFD analysis can be
invaluable in selecting a cooling strategy and refining a thermal
design by parametric analysis. In the final design phase, detailed
analysis of product thermal performance is performed to provide
boundary conditions for electrical performance analysis and reliability
prediction. In this regard, however, the lack of methods to accurately
predict electronics operational temperature, in terms of either
absolute temperature, or spatial or temporal temperature gradients, is
considered to hamper progress in reliability prediction.
Typically, the turbulent flow modeling capabilities of CFD
software dedicated to the thermal analysis of electronics have been
confined to zero-equation mixing length or standard two-equation
high-Reynolds number k-e eddy viscosity turbulence models. These models
meet the criteria of robustness, in terms of promoting stable
convergence, and to some extent, universality, which make them popular
for practical engineering calculations. They are by far the most
widely-used and validated, and are considered as computationally viable
in a design environment. Unfortunately, this approach is not entirely
satisfactory for modeling the thermal and kinematic complexity of
thermofluid problems in forced air-cooled electronic systems.
Using experimental benchmarks, CALCE has investigated the
capability of alternative low-Reynolds number eddy viscosity turbulence
modeling strategies, available in general-purpose CFD codes, to predict
electronic component heat transfer. Significant improvements in
predictive accuracy have been obtained relative to the standard mixing
length or high-Reynolds number k-e flow models. Such improvements would
enable parametric analysis of product thermal performance to be
undertaken with greater confidence, and contribute to the generation of
more accurate temperature boundary conditions for electronics
reliability assessment.
This could ultimately help reduce the current dependency on experimental prototyping.
Apart from the prediction of operational temperature in
application environments, the value of CFD in optimizing electronic
component assembly processes, such as convective reflow soldering, and
optimizing the thermal loads imposed in accelerated reliability tests,
such as powered air temperature cycling, has also been demonstrated.
Future work will focus on the development of improved modeling
methodologies for fan-, EMC screen- and vent- generated airflows, to
enable more accurate prediction of airflows within electronic
enclosures.
Enhancing the Limits of Air Cooling. Due to stringent
cost and reliability constraints, air cooling will remain an important
thermal management approach for many electronic products in the
foreseeable future. Considerable strides have taken place in
electronics thermal management over the last 15 years. Despite a
continued perception that the limits of air cooling have been reached,
the heat fluxes obtained by air cooling today could only be achieved
using liquid cooling in the late 1980s. In this context, proposing
universal heat flux limits for air cooling is misleading. CALCE is
addressing several key thermal management areas to help extend the
limits of air cooling.
Air cooling is traditionally associated with the use of heat
sinks, which are the most commonly-employed, cost-effective electronics
thermal management hardware. Heat sinks function by extending the
surface area of heat dissipating surfaces through the use of fins.
Their design and analysis is one of the most extensive research areas
in electronics cooling. Advances in heat sink cooling performance have
been achieved through progress in manufacturing technology and to a
lesser extent, fan design, thereby resulting in more efficient heat
removal from a given rectilinear volume. However, an efficient thermal
design needs to focus on the complete heat transfer chain of an
electronic system, from the heat dissipating components acting as
thermal source, to the environment external to the system enclosure.
Apart from convective and radiative heat transfer optimization, key
issues in advancing heat sink thermal performance therefore include:
- component-to-heat sink interface thermal contact resistance
minimization, which can be comparable to the actual heat sink thermal
resistance
- integration of heat spreading technologies, such as heat pipes and
high thermal conductivity materials, to minimize heat sink base
temperature rise
- integration of hybrid cooling solutions such as phase change materials (PCMs) to manage peak transient heat loads
- minimization of heat sink surface fouling, the impact of which on
thermal resistance is becoming a major warrantee issue in computer
products
Ongoing research at CALCE is addressing each of these areas. In
parallel with these initiatives, liquid cooling-based solutions are
being developed for applications where air cooling alone is not
sufficient to meet system thermal design specifications.
For further information on these efforts, please contact Dr. Peter Rodgers at 301-405-8126.
back to top
A three-year research grant, “Extension of Displacement Measurement
Techniques into Nano-mechanics Domain,?funded by Semiconductor Research
Corporation, ($300,000) was awarded for development of a measurement
technique for nano-scale deformation. The results of the proposed
research will be utilized to provide a mechanical reliability guideline
for interconnect technology for the current node and to identify
potential mechanical reliability issues for the 50-nm technology node
and beyond.
“Development of Experimental Apparatus using far Infrared
Fizeau Interferometry,?funded by Intel Corporation, a two-year research
grant ($200,000) awarded for development of a laboratory device to
measure warpage of packages and assemblies without any sample
preparation. The results of the proposed research will be used to
characterize the warpage behavior of current and future high
performance packaging solutions.
For further information, please contact Dr. Bongtae Han at 301-405-5255.
back to top
Dr. Michael Pecht, the George Dieter Chair Professor of Mechanical
Engineering, was granted Honorary Professor status at the Jiao Tong
University in Shanghai on June 8, 2004. The professorship will enable
him to establish a program at Jiao Tong on bio-electro-mechanical
health monitoring that will incorporate electronics and mechanical
engineering concepts with Chinese and Western medical philosophies. For
further information, please contact Dr. Michael Pecht at 301-405-5278.
back to top
Dr. Peter Rodgers joined the CALCE EPSC as a Research
Professor, where he supports the Center’s electronics thermal
management activities. He has extensive research and product
development experience in the thermal analysis of electronic equipment.
Dr. Rodgers was formerly with the Nokia Research Center, Finland, and
Electronics Thermal Management Ltd., Ireland, where he consulted on a
wide range of aspects in electronics cooling, spanning integrated
circuit (IC) packaging to facility cooling. He holds a Ph.D. in
mechanical engineering from the University of Limerick, Ireland.
Dr. Michael H. Azarian joined CALCE EPSC as a Research
Scientist. He holds a Ph.D. in Materials Science and Engineering from
Carnegie Mellon University, a Masters degree in Metallurgical
Engineering and Materials Science from Carnegie Mellon, and a Bachelors
degree in Chemical Engineering from Princeton University. He brings to
CALCE 13 years of professional experience in the data storage, advanced
materials, and fiber optics industries, having worked for Philips
Research Laboratories in Eindhoven, the Netherlands; W. L. Gore &
Associates, Inc. in Elkton, MD; and Bookham Technology in San Jose, CA,
as well as several start-up companies. He was most recently Manager of
Quality and Reliability at Bookham Technology in San Jose, CA. His
areas of expertise include reliability of photonic components, failure
analysis, and tribology of the magnetic head-disk interface.
back to top
|
