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FCI’s Problem Solving Approach
Changes Market
The FCI Electronics AirMax VS®
By Bob Hult
Every so often someone takes an entirely new approach to a problem and
comes up with a solution that offers advantages that change the shape of
the market. The FCI AirMax VS® may be just
such a solution.
 For
years the predominant approach to increasing the high-speed performance
of a backplane connector was to isolate signal pins with grounded pins
or metallic shields. Surrounding signal pins with a shield reduces
crosstalk between adjacent contacts and can create an electrical
environment similar to traces between ground plans on a PCB. Open pin
field connectors on a 2mm square grid can be used in higher speed
circuits, but as data rates increase, more pins must be dedicated to
ground, reducing the effective signal density. Connectors specifically
designed for multi-gigabit applications create controlled impedance
coaxial or twin axial shielded structures throughout the connector
signal path. Connectors designed for single-ended signaling are on a
consistent grid, while new generations of interfaces create shielded
coupled pairs for differential signaling applications. The result has
been a continuing improvement in connector bandwidth that today exceeds
10 Gb/s.
The integrated shield proved to be an effective solution, but adds
complexity and cost to the interface. Routing of the signal and shield
terminations to the PCB has become an increasing challenge to the
designer. Modeling of high-speed circuits has demonstrated that the
majority of signal distortion and loss occurs in the through-hole PCB
launch. Many suppliers recommend counterboring or drilling out unused
PTH plating to eliminate stubs that can cause reflections.
The market for high-speed backplane connectors was hit hard by the
recession that began in 2000, and in some cases delayed plans to bump
system speeds to new levels. Several large connector suppliers,
including FCI, introduced new interfaces such as the Metral 4000, which
offered a shielded stripline transmission structure and controlled
impedance specifically designed with bandwidth up to 3.125 Gb/s. Over
the next four years these suppliers filled out their product offerings
into complete interface families. During this same period advances in
silicon signal conditioning capabilities, such as pre-emphasis and
equalization, have extended the useable bandwidth of these connectors
into the 10+ Gb/s range.
FCI decided to take a new approach. The AirMax VS connector system was
introduced in 2003 and reversed several common assumptions. Rather than
use metallic shields for electrical isolation, this connector uses air
and staggered contact spacing to create a virtual shield.
The connector is assembled using insert molded leadframe assemblies (IMLAs)
that are capable of serving a variety of applications including
high-speed differential, low-speed single ended signals, and power. Each
IMLA performs electrically as a stand-alone unit. User defined pin
assignments determine how each signal line is
used, giving the designer a great amount of flexibility.
The column centerline spacing between IMLAs can be adjusted to match the
performance requirements of specific applications; 2mm for lower speed
and higher signal density applications, 3mm for higher performance and
ease of routing. The individual IMLA is application agnostic in that the
designer can mix signals and power within the same IMLA. This concept
can reduce the need to keep a variety of component parts in inventory.
Eliminating internal shields reduces insertion / extraction forces and
also permits a lower piece part price, which has created a new set of
cost expectations within the market.
Connectors are terminated to the PCB by compliant “eye of the needle”
pins in plated through-holes arranged in a 2 X 1.4mm offset pattern. 2mm
IMLA spacing permits one differential pair with 0.008 traces per routing
channel. while a 3mm column pitch allows two differential pairs to be
routed per channel. Increasing the number of traces per layer can reduce
the total number of PCB layers, further reducing cost.
Connectors are currently available in selected sizes of 3, 4, and 5 pair
configurations on both 2mm and 3mm column centerlines. Up to 10 IMLAs
can be combined into one connector assembly.
Guide/key hardware along with an ESD module assures proper alignment and
dissipation of static charges prior to contact engagement.
Bent pin contacts on the backplane have been a perennial complaint about
high-density backplane connectors for many years. The problem has only
gotten worse as pin counts increase and suppliers respond to demands for
higher density by reducing the size of the pin, making it more
susceptible to damage. FCI chose to minimize the problem by reversing
the sex of AirMax VS, putting a robust dual blade receptacle
(header)
on the backplane and the mating (beam)
header on the daughtercard. Many users have accepted this arrangement,
but old habits die hard, especially in the telecom market segment. As a
result, FCI has recently tooled a right-angle receptacle to permit board
extender applications as well as serve as the PCB header for I/O cable
assemblies, which are provided by W.L. Gore and Associates.
FCI has committed to tooling a vertical (beam)
header to mate with the right angle receptacle by mid-2005. Completing
the family will allow customers to choose standard or reverse sex
backplane configurations.
Signal contacts in the standard IMLA are conservatively rated to 0.5
amps each, but in applications requiring greater current, compatible
power modules have been developed. These press-fit modules are available
in 1X2 and 2X2 contact sizes and are capable of delivering up to 80 amps
on boards with 5 oz. copper PCB traces.
A license to tool an AirMax VS family of products has been granted to
Amphenol. Evaluation to confirm compatibility is in process and will
result in a fully functional and competitive second source for the
product line.
A variety of low- and high-speed signals, along with power, can be
sequentially mated to facilitate hot-mating requirements.
The latest extension of AirMax VS is the announcement of a Ball Grid
attached backplane receptacle.
 This
product, currently under evaluation, will address the signal distortion
generated by the plated through-hole launch of the connector. The BGA
attached version is designed to enhance high-speed performance by
optimizing footprint and routing options. A grid of surface pads will
replace plated through-holes. Small diameter or micro-vias will complete
the connection to internal backplane layers, eliminating the need for
counterboring. Parts are currently being evaluated internally and by
selected customers using leaded and lead-free solder, as well as with
and without mechanical PCB hold-down mechanisms. The production product
will incorporate features based on the results of these tests and will
likely be available later in 2005.
ConnectorSupplier.com Comments
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The AirMax VS
backplane connector system has broken new ground in high-speed
backplane connector design, offering excellent
performance, design flexibility and a lower price.
FCI has carefully orchestrated the introduction of the product to
insure that features match the benefits that prospective customers
are looking for. FCI and Lucent Technologies recently demonstrated
25 Gb/s data transmission using duobinary signaling architecture as
a step toward achieving 100 Gb/s Ethernet backplanes.
Product versatility is a key attribute that permits designers to
closely match their needs with off-the-shelf products, while
offering future performance headroom. AirMax VS provides this by
building the product around a universal contact assembly that can be
user adapted to specific application needs. A planned migration path
allows users to maintain a consistent connector platform throughout
the life cycle of their products.
AirMax VS is supported with accessories to provide power
distribution, static discharge, lower-speed Millipacs® contact
modules as well as alignment hardware.
The anticipated ability to offer both standard and reverse sex
configurations will open the product to a broader market in telecom
and computer related markets.
Expanding the capabilities of the interface to include ball grid
solder attachment should give a boost to the evolution away from
compliant pin termination. BGA termination on small interfaces such
as processor sockets has been universally accepted, but users are
very reluctant to apply this technology to large profile connectors,
which often experience large mechanical stresses in application. The
industry has very little data on surface mount solder joint failure
in backplane connectors as compared to compliant pin termination, a
process that has been fully documented. As users develop successful
experience with BGA termination processes, other suppliers will
begin to adopt this technology, which will likely become essential
as speeds exceed 10 Gb/s.
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Robert Hult, Director Product Technology -
Bishop & Associates, Inc.
 Bob
Hult has been in the connector industry for over thirty six years.
Robert began his career as a sales engineer for Amphenol. He
joined AMP in 1972 and served in several management positions
through 1996. In 1997 Robert joined Foxconn as Group Marketing
Manager for Intel, Chandler AZ. Prior to joining Bishop &
Associates, Robert was Regional Application Engineering Manager
for Tyco Electronics.
Robert graduated in 1968 from
Bradley
University with a BS in Electronics Technology and a minor in
business.
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