CALCE EPSC has developed proven methods for product design reviews
and company-based reliability capability assessment. In a competitive
marketplace, manufacturers cannot afford the expense and time involved
in producing and qualifying multiple versions of a product before
converging on a reliable design. Likewise, equipment manufacturers and
system integrators cannot wait until they get their parts or products
to determine if they are reliable. Such iterative development processes
are costly and preclude the achievement of rapid design cycles.
CALCE EPSC performs design reviews on electronic product
designs and prototypes, drawing on the expertise, virtual qualification
capabilities, and characterization facilities at the Center. The design
reviews aid customers in understanding the reliability risks in their
products before the products are released to the field. CALCE has
performed over three hundred such design reviews for leading
electronics manufacturers.
The CALCE reliability capability evaluation process was
developed to assist customers in assessing themselves, as well as
prospective suppliers, for their ability to design and manufacture
reliable products before they are delivered for use. It is based on
reviewing the reliability practices within an organization and
evaluating the effectiveness of these practices in meeting the
reliability requirements of customers. The CALCE reliability evaluation
process consists of:
-
Completion of a CALCE fact-finding data package by the company’s personnel
- A site visit by a CALCE evaluation team to cooperatively evaluate the company’s reliability objectives and practices
- A report incorporating all comments, observations and
recommendations, usually available within a few weeks after the evaluation
For information on CALCE reliability capability evaluation or CALCE design reviews, contact Prof. Michael Pecht or Dr. Michael H. Azarian or call 1+ 301-405-5323.
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The development of advanced sensor technologies offers industry many
new commercial and technical opportunities. Key features of sensor
technologies that drive widespread implementation across all sensor
types are low price, small size, robustness, dispensability, the
ability to be self-calibrating, and a high level of integration.
To help empower industry to make correct product and technology
investment choices, NEMI (the National Electronics Manufacturing
Initiative), in collaboration with CALCE EPSC, has developed a sensors
technology roadmap. CALCE EPSC has led the Sensors Technology Working
Group, which has analyzed technological and manufacturing capabilities
and compared these to existing and anticipated sensor applications. The
initial roadmap centers primarily on automotive applications for
sensors. Future efforts will examine applications across multiple
market sectors, including transportation, health care, consumer
electronics, industrial and telecommunications infrastructure, defense,
and security.
The application of MEMS technologies to sensors has great
impact on automotive applications. The shifting emphasis of MEMS
processing from bulk to surface micromachining is expected to enable
further miniaturization and reduced cost of MEMS sensors, opening new
applications. Subsystems in automobiles relying on advanced sensors
include engine control, safety systems, vehicle control, collision
avoidance, passenger comfort, and vehicle security. Legislation
governing tire safety for passenger vehicles is expected to drive
future growth in pressure monitoring systems.
Realization of the potential for embedded sensors will require
development of miniaturized sensor elements, integrated control
systems, and micro-actuators which can all be interconnected in a
single package with a small form factor. Advances in microelectronic
fabrication technologies, combined with system-on-chip design, will
lead to rapid development of the control systems needed for smart
embedded sensors. Packaging technology must evolve towards higher
levels of integration using system-in-package solutions, sometimes as
an intermediate step towards eventual system-on-chip implementation.
A number of important disruptive technologies (nanotechnology,
micro-fluidics, distributed sensing, advanced micro-optics) are poised
to have a substantial impact on the commercial marketplace for sensors
as we enter the next decade. Technology gaps hindering the full
realization of market opportunity exist for ultra-small and implantable
biosensors and self-contained sensors integrating miniaturized
energy-source technologies. The need exists for a wider selection of
biocompatible materials for packaging of biosensors, backed by
long-term reliability and safety data. Significant non-technical
barriers to sensor technology development include inadequate
cross-disciplinary collaboration, a shortage of qualified human
resources, and a lack of widely established and accepted
standardization, especially with respect to communication protocols.
For further information, please contact Dr. Michael H. Azarian or Dr. Sanka Ganesan or call 1+301-405-5323.
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CALCE is leading the technical analysis task force in the NAVY
Transformational Manufacturing Technology Initiative Robotic Solder Dip
Project for mitigation of tin whisker risk. Tin-lead or pure tin-plated
parts are prone to tin whisker formation, a major reliability concern,
especially for long-term and critical applications, such as those in
the fields of military or defense. One possible mitigation strategy
reflects the expectation that tin-plated IC devices could be refinished
by solder dipping to remove the tin plating by traditional eutectic
tin-lead plating. Questions remain regarding possible damage induced
inside the IC packages due to the thermal shock experienced during
solder dipping, and the effects of additional processing steps on the
quality of the plating.
This project, funded by the Office of Naval Research, studies
the effects of refinishing previously plated IC leads with solder
dipping. The key performers include the NAVY BMP Center of Excellence
(College Park, MD), Raytheon Missile Systems (Tucson, AZ), Raytheon
Integrated Defense Systems (Tewksbury, MA), Corfin Industries (Salem,
NH), and CALCE EPSC. The objectives include the following:
- Examination of dimensional properties of the lead cross sections,
plating and intermetallic layers after solder dipping in comparison to
the as-received parts
- Determination of whether the process results in deterioration of part reliability
- Determination of whether solder dipping has a detrimental effect on the moisture sensitivity level of the parts
These objectives are being addressed by studying the following key areas:
- Dimensional changes and geometrical issues for the new finish
- Formation of intermetallics
- Thermal degradation at package interfaces leading to delamination
- Dissolution of the pre-existing plating
- Wetting of leads with new solder-dipped finish
Issues related to handling damages and coplanarity are also being investigated.
Twenty-three different electronic parts have been selected for
this evaluation, covering various package types, plating materials,
lead materials, and lead pitch. The parts go through five major stages
during the evaluation process: inspection of as-received parts, initial
electrical testing, solder dipping, post-dip electrical testing, and
environmental (temperature cycling and temperature humidity) exposure.
CALCE is evaluating parts taken off the flow after each stage
for possible damages that may have been caused by the solder-dipping
process. Conclusions on the effects of refinishing by solder dipping
are made by comparison of these test results across the different
process stages. Various destructive and non-destructive tests, along
with analysis techniques, are deployed to evaluate the parts at each of
these stages. The result of these analyses will be a guideline document
on the applicability of the solder-dipping process for various part
types.
For more information, contact Dr. Diganta Das at 1+301-405-5770, or Dr. Sanka Ganesan at 1+301-405-0765.
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As the electronics industry transitions from conventional tin-lead
(SnPb) solder to lead-free solders (e.g., tin-silver-copper (SnAgCu), a
great deal of time and effort has been spent on conducting tests to
determine the reliability of the new solders. A review of the test
results reported in the open literature is encouraging in that the
durability of the SnAgCu solder for compliant leaded and area-array
technologies appears to be superior to joints formed with SnPb.
However, there have been instances where the Pb-free interconnects
appear to be less durable (fail sooner) than their SnPb counter-parts.
From these conflicting results, it is clear that a transition region
exists where SnPb interconnects are likely to outperform Pb-free
interconnects, and visa versa. The actual crossover is dependent on the
stress-strain history in the solder, which in turn is influenced by
temperature and dwell times. As a result of early test failures,
concern has arisen that certain Pb-free solders may not be suitable for
some use (application) environments.
In order to fully understand the impact of solder change on
interconnect durability, CALCE is conducting a designed experiment to
examine the influence of cyclic temperature and dwell time on the
fatigue life of Pb-free solders (SnAgCu and SnAg), as compared to SnPb.
The test specimen for this experiment is a printed wiring assembly with
four ceramic chip carriers attached to the printed wiring board. The
chip carriers are attached to the printed wiring board with SnPb,
SnAgCu, and SnAg solders. Testing is being conducted to 100% failure.
Thus far, the major finding has been that elevated temperatures
and extended dwells have a stronger influence on reducing the solder
attach life of Pb-free (SnAgCu and SnAg) solders than on SnPb solder.
In fact, when the peak temperature was held at 125ºC, raising the
cyclic mean temperature resulted in a shorter life for Pb-free solders
than for SnPb solder for the components under test.
While the testing has not demonstrated a greatly elevated
reliability risk with Pb-free solders, it has clearly demonstrated that
the acceleration factor on Pb-free solder joints is substantially
different from that on SnPb solder joints. It also raises the question
of the adequacy of existing modeling techniques for determining
acceleration factors between product qualification tests and field
conditions.
The results from these tests are being used to update the
rapid life assessment models within calcePWA software and the model
constants and strategies used for detailed finite element modeling of
unique solder geometries. The update to the calcePWA software will
allow simulation-assisted reliability assessment (SARA) for Pb-free
electronic hardware. This simulation capability is being used by many
organizations to review product designs that are transitioning to
Pb-free assemblies. With the knowledge gained from these test results,
CALCE Consortium members will have greater confidence in conducting
qualification tests and relating those test results to field life
requirements.
For more information of the Pb-free efforts being conducted by CALCE and how to participate in these studies, please contact Dr. Michael Osterman at 1+301-405-8023.
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CALCE has been active in assessing the shock loading reliability of
electronic products. CALCE is now working with the Army Research Labs
(ARL) and the University of Nevada, Las Vegas, in a multi-year project
that will identify the most dominant failure sites and failure
mechanisms in high-G, gun-launched smart munitions containing
electronic components and assemblies. The project is considering
gun-launch conditions ranging from current artillery peak G-level
setback loads of 15,000 G through next-generation artillery of 60,000+
peak G-levels. Only one-directional G-loading is being considered. Spin
is not being considered, as next-generation smart munitions will
typically not be launched through rifled gun tubes.
The first objective of the project is to provide electronic
assembly and component selection design guidelines for high-G
applications. The final objective is to develop validated design models
and methodologies that can be used for the rapid reliability assessment
and virtual qualification of electronic assemblies in smart artillery
projectiles.
As next-generation electronic components become available and
there is need for them to be considered for use in high-G environments,
a generic approach is necessary. The practical objective of the current
task is to evaluate a subset of current-generation components and
develop failure models and virtual qualification tools that apply to
these components. This subset of components is being selected based
upon usage and ruggedness concerns expressed by designers and UMD/ARL
experience. The key deliverable from this task will be a demonstrated
methodology and approach to reliability assessment that can also be
applied to future electronic components that will be subjected to
artillery launch loads.
The task relies upon an integrated experimental and computer
simulation-based approach. It brings together the talents of the
University of Maryland’s CALCE Center with its physics of failure
experience and approach to electronics reliability assessment, ARL and
its experience and facilities using air guns to simulate artillery
launch loads, and UNLV and ARL with their dynamic FEA modeling
experience. In very general terms, an experimental program will be
conducted to generate a well-characterized failure database of
components and assemblies subjected to high-G loads. Computer
simulation will be used to quantify the exact load or stress levels at
each identified failure site.
Most researchers investigating high-G level failures in
electronics rely upon computer simulation only and hypothesize about
potential failures. This is a good starting place, but the hypothesized
failure models need experimental confirmation to understand such
details as dynamic strength versus static strength. Additional issues
such as the dynamic interaction of the mitigator material and the
interaction of the various types of potting compounds can only be
answered via carefully designed experiments. Due to high costs in time
as well as money, a wide enough variety of careful experiments has not
previously been conducted to accurately develop failure models for
electronics in a high-G environment.
For more information, please contact Prof. Don Barker at 1+301-405-5264.
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As integrated circuit (IC) progress has driven more functionality
onto each integrated circuit die, fewer ICs have been required on each
printed wiring board. At the same time, the trends toward lower IC
voltages and to higher operating frequencies have required more
passives to maintain signal integrity. For example, approximately 90%
of the electronic components on a cell phone are passive components, of
which 60% are capacitors, and most of these capacitors are multilayer
ceramic capacitors (MLCC). Capacitance has been improved by reducing
the dielectric thickness between electrodes, by increasing the number
of electrodes, and by introducing new, smaller capacitor sizes. The
smallest capacitor size in volume production is only 0.6 mm by 0.4 mm
by 0.2 mm (EIA 01005), approximately the diameter of a human hair.
MLCC electrodes and terminations had been composed of an alloy
of palladium and silver in order to make the melting temperature
compatible with the sintering temperature of barium titanate. Beginning
in the late 1990s, the price of palladium rocketed from $125 to almost
$1100 per troy ounce. The capacitor industry responded by making
electrodes with nickel, a design referred to as base metal electrodes
(BME). Today, most MLCCs are BME parts.
Barium titanate is used in capacitors because it has a high
dielectric constant as a result of its atomic structure. Barium
titanate at room temperature has a tetragonal (cuboid) shape. The
titanium atom in the center position of a barium titanate cuboid is
often described as a “rattling titanium” atom, because it can be in one
of two positions along the unit cell’s longer direction. Within each
crystalline grain of barium titanate there are domains that are
separated by nanometer scale transitions called walls. Within each
domain, titanium atoms are positioned in one head-to-tail direction. In
the adjacent domain, the titanium atoms are positioned in the opposite
direction. The ordering might be envisioned as vehicles on strips of
highways laid next to another.
Application of a voltage to the MLCC generates an electric
field between electrodes that forces individual titanium atoms to
switch positions to line up with the field, creating a polarization.
Many unit cell polarization vectors combine to generate what we measure
as net capacitance.
It was already known that barium titanate capacitors lose
capacitance over time due to changes in mechanical stresses in the
barium titanate after firing. This “aging” effect involves atomic
adjustment of stresses within the crystalline grains and tends to be
very gradual. Designers build in capacitance margin over product life
to allow for this type of aging. However, when BME capacitors are
exposed to moisture, they can exhibit another type of aging.
The new aging was first discovered when both precious metal and
BME EIA 0805 capacitors were subjected to autoclave (120ºC/100%RH)
testing. It was found that the precious metal capacitors aged according
to the well-known aging mechanism (less than 3% from their starting
values), but the BME capacitors degraded to below the -30% criterion at
500 hours of exposure. Attempts to restore the capacitance after the
autoclave exposure, using a standard industry method called deaging,
produced different results for the precious metal and the BME
capacitors. The PME capacitors returned to their initial values, but
the BME capacitors did not recover. This is because the humidity
degradation mechanism is different than the mechanism for the known
aging.
The reasons for this new failure mechanism are complex, and two
theories were hypothesized. The first was that there could be oxidation
or corrosion of the nickel plates. However, ion beam milling and
electron microscopy of the electrode-to-dielectric-to-termination
interface, electron backscatter diffraction (EBSD) of the
polycrystalline grain structure of the capacitors, and dye penetrant
found no possible interconnected path for moisture to flow into the
capacitor body from the capacitor surface. Capacitors were also
monitored for weight gain after various moisture exposures using
balances and thermogravimetric analysis (TGA) with argon purge gas. No
weight change was detected by either method, and it was finally
concluded that moisture could not be entering the capacitor bodies.
Finally, BME capacitors were subjected to long-term autoclave and then
internally assessed using x-ray photoelectron spectroscopy. It was
found that nickel oxide was not in the body of the capacitors. In other
words, the decrease in net capacitance was not due to plate oxidation
or increased plate spacing from an oxidation process.
The other hypothesis was that the loss of capacitance was due
to oxygen vacancies. When a barium titanate unit cell loses an oxygen
atom, we call that an oxygen vacancy. If this oxygen vacancy is a
random defect, there is no measurable change to the net capacitance.
However, if many barium titanate unit cells loose an oxygen atom, then
there will be a net reduction in capacitance. The capacitance loss can
be significant if multiple cells affected by oxygen atom loss are lined
up.
In order for oxygen vacancies to move within the capacitor,
they must cross crystalline grain boundaries in the barium titanate.
Since the size of the dielectric grains does not change as the industry
shrinks capacitor size, and shrinking the size implies thinner barium
layers between electrodes, there are fewer grains that ions must cross.
With fewer grain boundaries to cross, there is less resistance to ion
flow. In addition, as the MLCC size shrinks, the ratio of the surface
area – where the barium atoms are being removed – to volume grows,
bringing the surface charge and oxygen vacancies into more intimate
interaction. In these two ways, reducing the size makes the newer BME
capacitors more vulnerable.
Experiments showed that the new aging followed an exponential
rule, just as would be expected in a diffusion process. This process
can occur in the autoclave testing and perhaps in the field due to
long-term humidity exposures. The result is degradation of capacitance.
Capacitor degradation due to the new aging is most problematic in
high-humidity environments, with high-value capacitors (thinner barium
titanate layers). Unfortunately, standard humidity life testing, such
as JESD-22 THB, HAST and autoclave, will likely not uncover this
problem. Therefore, poor reliability due to degradation of BME MLCC
capacitance may catch manufacturers and consumers by surprise.
To obtain more information on humidity degradation of base metal electrode multilayer ceramic capacitors, please contact Prof. Michael Pecht at 1+301-405-5323.
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Electronic parts are subjected to transient thermal environments in
the course of their life, induced by assembly processes or dynamic
operating conditions. In such conditions, large spatial and temporal
temperature gradients can develop in electronic packages and assemblies
that can adversely impact device reliability or electrical performance.
Progress in electronics reliability prediction has been
hampered by the lack of methods to accurately predict such temperature
gradients. Numerical analysis of heat transfer in electronic equipment
has generally been confined to steady-state operation. This is
essentially attributed to previous reliability prediction methods
focusing on steady-state temperature, design for continuous operation,
and prohibitive computational requirements for transient analysis. To
further ease computational constraints, numerical analysis of transient
component heat transfer is generally undertaken using non-conjugate
methods. Such analyses are confined to the modeling of conduction, with
convective heat transfer represented by a semi-empirical effective heat
transfer coefficient prescribed at the solid-fluid interface. This
approach is not appropriate for the majority of air-cooled
applications, or for convectional reflow soldering processes, in which
board heat transfer is highly conjugate.
CALCE EPSC has assessed the need for conjugate
(conduction/convection) analysis, both for component temperature and
thermomechanical behavior prediction in operational, assembly, and
reliability qualification environments. The capability of computational
fluid dynamics (CFD) analysis to predict component transient conjugate
heat transfer in air temperature and power cycling conditions
representative of reliability qualification tests or assembly processes
was investigated using an industry-standard CFD code for the thermal
analysis of electronics. Based on a range of experimental benchmarks,
component transient thermal behavior was found to be accurately
predicted for a single board-mounted PQFP. The results suggest that CFD
analysis could play an important role in providing critical temperature
boundary conditions for component electrical performance and
thermomechanical behavior analyses, designing component reliability
qualification tests involving power and air temperature cycling, and
optimizing convective assembly processes. The need for accurate virtual
prototyping of assembly processes is emphasized by the introduction of
lead-free technology, which will require extensive requalification of
the reflow processes, partly resulting from higher reflow temperatures
relative to eutectic lead-tin solder. The transient thermal analysis
approach investigated by CALCE could contribute to more accurate damage
estimation and life prediction due to specific failure mechanisms
influenced by temperature, relative to predictions obtained using
non-conjugate heat transfer solution methods.
Future work will investigate the impact of both more complex
aerodynamic conditions and component thermal interaction on the
prediction of transient heat transfer for forced-air-cooled,
multi-component board applications.
For further information, please contact Dr. Peter Rodgers at 1+301-405-8126 or Dr. Valérie Eveloy at 1+301-405-5901.
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The CALCE Center and the University of Massachusetts, in
collaboration with PartMiner Information Services, Inc., have been
awarded an NSF grant to explore how existing academic and industrial
resources can be combined to significantly impact proactive
obsolescence forecasting and management.
CALCE will work on a data-mining-based approach to electronic
part obsolescence forecasting. Part obsolescence dates (the date on
which the part is no longer procurable from its original source) are
important inputs during design planning. Most electronic part
obsolescence forecasting algorithms are based (at least in part) on the
development of models for the part’s life cycle. Traditional methods of
life-cycle forecasting utilized in commercially available tools and
services are ordinal-scale-based approaches, in which the life cycle
stage of the part is determined from an array of technological and
market attributes. Existing commercial forecasting tools are good at
articulating the current state of a part’s availability and identifying
alternatives, but are limited in their capability to forecast future
obsolescence dates and cannot provide quantitative confidence limits
when predicting future obsolescence. More accurate forecasts, or at
least forecasts with a quantifiable accuracy, open the door to the use
of life-cycle planning tools (like that CALCE Mitigation of
Obsolescence Cost Analysis - MOCA tool) that could lead to more
significant sustainment cost avoidance.
In this NSF grant, CALCE will demonstrate the use of
data-mining-based algorithms to augment commercial obsolescence risk
databases, increasing their predictive capabilities substantially.
Several years ago, the University of Maryland developed an obsolescence
forecasting methodology based on forecasting part sales curves. In this
method, sales data for an electronic part is curve fit. The attributes
of the curve fits (e.g., mean and standard deviation for sales data
fitted with a Gaussian) are plotted, and trend equations are created
that can be used for predicting the life-cycle curve of future versions
of the part type, (Solomon et al., IEEE Trans on CPMT, Dec. 2000). The
original obsolescence forecasting approach used a fixed window of
obsolescence determined as a fixed number of standard deviations from
the peak sales year of the part. An extension of this methodology that
increases the accuracy of the forecasts is the calculation of
electronic part vendor-specific windows of obsolescence using
historical last-order or last-ship dates. The extended methodology will
not only enable more accurate obsolescence forecasts but will also
generate forecasts for user-specified confidence levels. The
methodology will be demonstrated on both individual parts and modules.
Initially the data mining methodology has been applied to part
types with well defined primary attributes, e.g., flash memory. The
methodology has also been demonstrated on composite structures such as
memory modules. Preliminary results from this work will be presented at
the DMSMS Conference in Nashville, TN in April. Extensions of the data
mining approach to part types with either multiple driving attributes
or indeterminate driving attributes is the focus of the work to be
performed in this project during 2005.
For further information on this work, contact Prof. Peter Sandborn at 1+301-405-3167.
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Samsung Techwin Engineers and Prof. B. T. Han won the Gold Award for
the best paper in the Analysis and Simulation Session at the 1st
Samsung Technical Conference held on November 9–12, 2004. The title of
the paper was “Predictive Modeling Solutions for Next Generation LCD
Driver IC Chip Package.” For more information please contact Prof. B.T. Han at 1+301-405-5255.
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Dr. Diganta Das and Dr. Peter Rodgers have been invited to give a
one-day professional development course entitled “How to Select and Use
Electronic Parts Outside the Manufacturer-Specified Temperature Range”
at the 21st SEMI-THERM symposium, to be held in San Jose, CA, March 13,
2005. This course presents specific methodologies for uprating of
electronic parts. The course is meant to support the complete supply
chain that may provide or use uprated parts, including product
manufacturers, electrical test laboratories, aftermarket part
suppliers, regulatory bodies, and part manufacturers. Further
information and registration details for this course are given at http://www.semi-therm.org.
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Dr. Valérie Eveloy has joined CALCE EPSC as a Research Scientist.
She holds a Ph.D. degree in mechanical engineering from Dublin City
University, Ireland, and a M.Sc. degree in physical engineering from
the National Institute of Applied Science (INSA), France. She has been
involved in the thermal management, packaging, and reliability of
electronic equipment for ten years, and was previously with Nokia,
Finland, and Electronics Thermal Management Ltd., Ireland. Her current
activities at CALCE EPSC are focused on human health monitoring. Other
research interests include electronics thermal management and
computational fluid dynamics. She has authored or co-authored over
thirty-five journal and conference publications. Dr. Eveloy is a member
of several international conference program committees focused on
thermal phenomena in electronic systems.
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CALCE EPSC has recently acquired a TC ProbeTM thermal conductivity
instrument from Mathias Instruments. This equipment is designed to
measure the thermo-physical properties of solids, liquids and greases
using a non-destructive technique. This instrument also enables
depth-profiling and changes in thermal properties to be assessed over
time as the result of physical and/or chemical processes occurring
within the sample. This equipment will extend CALCE’s thermal interface
material (TIM) research capabilities. CALCE EPSC currently has a laser
flash unit that permits the measurement of bulk and interfacial thermal
contact resistance of interface materials, such as adhesive-based
materials (e.g., epoxies and pressure sensitive adhesive tapes) and
solders. For further information, contact Dr. Peter Rodgers at 1+301-405-8126.
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