US Headquarters
8851 SW Old Kansas Avenue
Stuart, FL
34997
USA
UK Headquarters
4th Floor 11
-12, St. James’s Square
London
SW1Y 4LB
United Kingdom
US: +1 772 286 9300
UK: +44 20 7004 1600
smithsinterconnect.com
info.us@smithsinterconnect.com
info.uk@smithsinterconnect.com
Filter Capacitor Comparison
The heart of the filter connector is the capacitor array. Smiths Interconnect uses
monolithic ceramic capacitor array on both thick and thin film technology. Using a dry
process to laminate the layers of X7R ceramic tape, Smiths Interconnect is capable of
achieving capacitance values from 100pF to 100nF on the same array. Our extensive
filtering capability allows for unique applications and arrangements not engineered
elsewhere in the connector world. This may include mixed contact sizes, new insert
arrangements, or high voltage applications up to 2000VDC Dielectric Withstand Voltages
(DWV).
The planar array is much more complex and versatile in its design. The planar uses
the same X7R material as the tubular capacitor, however the electrodes run
perpendicular to the contact. This allows higher capacitance and higher voltage
ratings, as the pin to pin spacing does not affect the design as much. With the
electrodes running perpendicular to the contact, we can stack more electrodes thus
increasing capacitance and at the same time, thicken the dielectric between
electrodes to increase withstanding voltages.
The planar array also has the advantage of strength. As the layers of ceramics are stacked
perpendicular to the contact, we can increase the planar thickness to about .100" to
withstand high vibration scenarios as in the EFA. This far outweighs the .015" found in the
Tubular capacitor. Because the capacitor is ceramic, it is relatively brittle in comparison to
the other components of a connector (metal, rubber, and plastic). Therefore, the internal
construction of the filter connector must isolate the capacitors from mechanical stress.
Smiths Interconnect uses a thin wall ground plane to house the filter elements. The
ground plane is captured between halves of the connector shell to provide mechanical
retention as well as electrical contact. Thermal stress from the connector shell is not
transferred to the capacitor arrays due to a gap between the outside diameter of the
ground plane and the inside of the shell. Stress from the contacts is eliminated through
the use of a block of epoxy on either side of the capacitors. Smiths Interconnect further
isolates the capacitors with a proprietary expansion barrier between the epoxy and the
capacitors. EMI/RFI and EMP protection can both be integrated into a connector with
only a small increase in length over the non-filtered version. Smiths Interconnect’s design
approach for diode connectors is unique. Smiths Interconnect mounts the diodes around
the outside of the contact arrangement on a multilayer circuit board within the
connector.
US Headquarters
8851 SW Old Kansas Avenue
Stuart, FL
34997
USA
UK Headquarters
4th Floor 11
-12, St. James’s Square
London
SW1Y 4LB
United Kingdom
US: +1 772 286 9300
UK: +44 20 7004 1600
smithsinterconnect.com
info.us@smithsinterconnect.com
info.uk@smithsinterconnect.com
Tubular Capacitor Technology
In the early 1980’s the filter connector (still in its infancy) used exclusively tubular type
capacitors. These capacitors served the needs of the industry well at that time. However,
low yields and an array of quality problems suggested that the tubular capacitor was no
longer sufficient for the systems it was designed into. Therefore, in the late 1980’s the
monolithic planar array was born into existence. This new technology incorporated the
monolithic chip capacitor technology and adapted it to a multi line configuration. This
gave both the ability to achieve higher capacitance per line as well as higher withstanding
voltages. The two technologies are vastly different in their design and capabilities.
The tubular capacitor is, as it suggests, a tube running the length of the contact with
electrodes buried inside. The wall thickness of the tube is dictated by the pin to pin
spacing of the connector, the metal ground plate used to ground the capacitor, and the
size of the ferrite in a Pi section filter. In a 150 line ARINC 600 module, the pin’ to pin
spacing is .100". Therefore the wall thickness of the tube is .050" minus the web
dimension of the ground plane minus the wall thickness of the ferrite. Typically it ends up
being around .015" thick. This limited thickness has to be designed to withstand the
voltage rating of the system, achieve the desired capacitance and be strong enough for
system vibration.
The systems of today typically require much higher capacitance values and/or require
higher voltage ratings. The Eurofighter Typhoon has several requirements that exceed
2000 VDC and the vibration requirements are the highest in the industry. The .015"
tubular capacitor is not designed to handle these high vibration requirements and there
is no space to increase either the capacitance or the voltage rating. Today's systems
mandate harsh environmental constraints to be subjected to component hardware. The
dielectric material in the capacitor typically is X7R type material to achieve the highest
capacitance with the least change in capacitance over the temperature range. The tube
has the electrodes (which when stacked together increase capacitance) running parallel to
the contact. This in combination with the pin to pin spacing limits the capacitance to
about 7000 pF at 200VDC.
Chip Capacitors
The use of chip capacitors in military applications is typically not allowed in connectors.
The reason is two fold: first chip capacitors tend to resonate at frequencies around 200-
300 MHz and during a swept EMC test tend to fail at those frequencies. They also take up
too much space and tend to lower the MTBF rating of the connector as a whole. The