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Technical
Articles & Papers
Nelcote Advanced Composite
Materials
Nelco Electronic, RF and Microwave Materials
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Evaluating
Laminates for High Temperature Assembly (1 Mb)
By Silvio Bertling
As printed in
The Board Authority, September 2005
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Abstract: The RoHS
and WEEE Directive in Europe is the driving force for the
implementation of high temperature lead-free assembly around the
world. As designers struggle with these new goals, questions
regarding the integrity and reliability of various high temperature,
lead-free assembly capable laminates continue to rise. In short, the
fabricators and end users must select a laminate which can meet the
rigorus demads of lead-free solder assembly. Unfortunately, at this
time there is no standard test methodology that consistently and
accurately assists in determining which laminates fall into this
category. This article introduces a test procedure that utilzes a
daisy chain TV designed by IPC PCQR2 suitable for both reflow
testing and HATS (Highly Accelerated Thermal Shock) testing.We
believe that this procedure can be used to determine how well a
particular laminate performs when exposed to 6x reflow, thermal
cycling and a combination of reflow and thermal cycling.
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Best
Materials for 3-6 GHz Design (226k)
By Douglas Leys
As
printed in Printed Circuit Design & Manufacturing, November 2004 |
Abstract: Wireless
communication and broadband applications are moving digital
circuitry into the analog world. High-speed circuit designs
emphasize the usefulness of passive circuit elements. When designing
below 1 GHz, passive elements such as the dielectric substrate can
generally be ignored and standard FR-4 materials usually work very
well. But as frequencies increase beyond 1 GHz, the passive circuit
elements must be taken into account. Primary considerations for
circuit design in the 3-6 GHz arena include skin effect, surface
roughness, proximity effect, EMC and dielectric substrate. This
article will cover dielectric substrates and the related properties
to consider when choosing materials for your high-frequency design. |
Conductive
Anodic Filament (CAF): The threat to miniaturization of the Electronics
Industry (488k)
By Konstantine (Gus) Karavakis and Silvio Bertling
As presented
at MEPTEC October, 2004 and reprinted in
CircuiTree Magazine, December 2005 |
Abstract: Conductive
anodic filament (CAF) occurs in substrates and PCB’s when a Cu
conductive filament forms in the laminate dielectric material
between two adjacent conductors or plated through vias under an
electrical bias. CAF can be a significant and potentially dangerous
source of electrical failures in IC packaging substrates, PCBs and
the overall system (package, module) that they are part of. The
increased board density which has being driven by the chip scale
packaging (CSP) revolution in the early 90’s, along with the
increased I/O density on the chips, has forced the PCB industry to
decrease via wall to wall distances and feature sizes. This path of
the electronics industry of placing as many components as possible
in a minimum of PCB “real estate” area has increased the reliability
requirements for bare PWB’s and is raising concerns of possible
reliability issues caused by conductive anodic filament formation
within the multilayer structure.
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PWB
Dielectric Substrates for Lead-Free Electronics Manufacturing
(250k)
By Douglas Leys and Steven P. Schaefer
As
presented at IPC Expo 2003 |
Abstract: In order to
safely accommodate the increased thermal and mechanical requirements
of lead-free assembly technology, extensive testing of the printed
wiring board (PWB) substrate is required to confirm that there are
no compromises in performance and long term reliability when moving
away from lead. This paper
presents a comparison of four (4) different commercially available
PWB substrate materials, including one produced specifically to
handle lead-free soldering, using both traditional thermal shock
testing and accelerated thermal cycling. The use of the Interconnect
Stress Test (IST) was chosen for the accelerated life cycle test. A
generic 22 layer PWB test vehicle was subjected to various
pre-conditioning environments in order to simulate the stress
generated during both lead-containing and lead-free assembly. These
test vehicles were then cycled to failure. Using this test
methodology, this paper will allow the reader to obtain a
comparison, under lead-free assembly test conditions, of the
traditional thermal robustness tests with the IST thermal cycling
test. It will also provide an indication of the impact on the PWB of
moving from a lead-containing assembly environment to one that is
lead-free. |
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Multilayer
Material Technology for Improved Signal Integrity in the Region
Above 5 GHz (144 k)
By Leena Gulia, Fred Hickman & Bob Forcier
As printed in
The Board Authority, September 2001
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Abstract: Substrate
materials that provide low Dk and low loss properties have become an
essential element of
high-speed digital and analog systems. In some sense, achieving a
solution for providing excellent signal integrity
within a high layer count design has become “The Holy Grail” in the
OEM community. Traditional epoxy/glass materials fail to meet the
electrical performance required of many new designs. OEMs that
produce high-speed optical routers, switches, networks, servers,
etc., all require materials with lower dielectric constants (Dk) and
dissipation factors (Df) to further improve the performance of their
products. The lower Dk allows them to run
faster signal speeds and higher packaging densities by retaining
nominal impedances with thinner dielectrics. The lower Df enables
them to run longer traces, use less incident power, and improve the
overall integrity of the signal.
Although low Dk and low Df properties have already been produced in
RF/microwave materials, existing material
systems do not have the ability to produce ultra-thin dielectrics
and subsequent multilayer structures with higher layer counts.
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High
Reliability/Low CTE Epoxy Technology: An Overview of the Advantages
of Low CTE Materials (563 k)
By Bob
Forcier and Bob Schor
As printed in
CircuiTree Magazine, February 2001
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Abstract: As board
reliability requirements have increased over the last several years,
the multilayer industry has been enthralled with the continuing
trend towards higher Tgs. For example, in North America, over 50% of
the
multilayer boards 12-layers and above (or ≥ 0.090" thick) typically
require a minimum material Tg of 160°C or higher. This strategy of
using higher Tg systems has been successful in producing higher
yields in products that
must survive the difficult thermal excursions experienced in
assembly and BGA rework. Perhaps the most significant benefit of
high Tg systems is the lower Z-axis expansion of the product when
measured over a temperature range. The higher 170°C Tg resin system
provides up to 22% less expansion when compared
to standard 140°C Tg system (3.9 vs. 5.0%). This lower expansion
minimizes the fatigue that a plated-through-hole would experience
during a thermal excursion. Less expansion equates to less fatigue
in the plated copper that might lead to reduced electrical opens of
the plated-through-hole.
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Laser
Drillable E-Glass Multilayer Materials... An Overview of Laser Enhanced
Materials (117 k)
By Bob
Forcier
As
printed in The Board Authority, July 2000
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Abstract: One key factor
of a new family of materials that enables easier laser drilling is
the weaving and post-weaving processes implemented by the glass
fabric suppliers. By careful formation of the glass fiber bundles,
the
glass manufacturer can provide a flatter bundle in both the warp and
the fill directions as compared to the rounder bundles usually
associated with standard E-Glass weaving technologies. Included in
this new process is a spreading of the glass fibers to achieve a
more even glass distribution across the entire area of the fabric.
In this manner, the fabric has a smaller range of highs and lows in
glass density. |
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AGATE
Program Helps Streamline Material Certification Process
(13 k)
By
John Tauriello
As
printed in High-Performance Composites Vol 8, No. 3, May/June 2000
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Abstract: Airplane
manufacturers are responsible for time-consuming and expensive FAA
certification testing to qualify every composite combination for use
in each aircraft design. The high cost of testing tends to limit
composite use to large commercial aircraft, leaving
non-FAA-certified experimental kit planes on the cutting edge of
design in the general aviation arena. As a Boeing engineer pointed
out, one widely used carbon/epoxy composite sold by a single company
has 34 different procurement specification databases governing its
sale.
The certification process will become considerably easier thanks to
the AGATE (Advanced General Aviation Transport Experiments) program.
Begun in 1995, AGATE is a wide-ranging public/private consortium
effort aimed at making U.S. general aviation more affordable and
safer. AGATE involves more than 70 entities, including the National
Aeronautics and Space Administration (NASA), the FAA, aircraft
manufacturers, universities and composites suppliers. The endeavor
encompasses training, safe ways to utilize air space and
improvements in ground infrastructure systems, in addition to
promoting wide use of composite materials. According to John
Turiello, director of marketing and sales at FiberCote Industries
Inc. (Waterbury, Conn.), AGATE includes a streamlined material
certification program with preapproved supplier databases that will
enable composite aircraft parts and assemblies to be designed and
built in as little as one-half the time currently required. |
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A
Composite Material Qualification Method That Results in Cost, Time
and Risk Reduction
(353 k)
By
John Tauriello, Sean Doyle & John S. Tomblin (Wichita State
University)
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Abstract: One of the
largest single regulatory hurdles for an airframe manufacturer,
i.e., user, of polymer based advanced composite materials in
certified aircraft applications, is to generate design allowables
that will satisfy Federal Aviation Regulations (FARs). Due to the
lack of a regulatory mechanism that encourages materials users to
share data, historically each user has independently executed coupon
level test plans and design allowable programs for specific
materials - a costly and time consuming process. Design allowables
for similar or identical materials have often been generated
consecutively by several users as a routine part of their
certification efforts, which has resulted in redundant costs to
users, materials manufacturers and regulators. A new composite
materials qualification methodology has been developed by members
the Advanced General Aviation Technology Experiments (AGATE)
consortium. Based on Military Handbook 17 (MIL-HBK-17)2 guidelines,
the "AGATE Method" describes a "standardized" coupon level material
qualification test plan and statistical technique that yields lamina
design allowables for a specific material system, such that
allowables can be shared among multiple users without each user
having to repeat the full qualification procedure. Once the original
qualification database is completed and its resultant design
allowables are approved for use by the FAA, each user needs only to
perform a limited "equivalency" test plan to verify that their
process yields properties that are equivalent to the original
database. |
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The
Design and Fabrication of HDI Interconnects Utilizing Total Integration
of Fiber-Reinforced Materials... An Overview of Fiber-Reinforced
HDI Material Options (119 k)
By Bob
Forcier and Fred Hickman
As
printed in The Board Authority, March 2000
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Abstract: It is now
possible to produce HDI products, including high layer count
backplanes and microvias, without the use of resin-coated coppers or
SBU-type dielectrics. Typically, the microvia HDI world has been
fueled by utilizing a resin-coated copper technology or other
non-reinforced materials to comprise the outer dielectrics of the
multilayer. However, fiber reinforcement in all dielectrics can
provide many benefits to the HDI designer and the printed circuit
fabricator. Although the use of resin-coated copper continues to
grow, the alternative of using fiber-reinforced materials provides
more flexibility of resin systems and thickness in any given HDI
design. As the designs become more complex, and the layer counts
increase, fiber-reinforced materials offer lower Z-axis expansion,
lower X-Y expansion rates, more thickness latitude, resistance to
cracking, and a wide variety of resin options not possible with
other approaches. This article explores the use of various
fiber-reinforced material technologies for HDI as compared to
resin-coated copper constructions. |
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