Capacitor technology leads to vibration proof filter connectors

New technology is replacing a filter connector’s planar array block capacitor with a state-of-the-art flexible circuit and individual surface mounted chip capacitors. Bob Walker explains

Today’s high-reliability military, aerospace and industrial applications require more rugged and lightweight filter connectors. The filter connector provides a stray signal barrier upstream and away from electronic devices to protect critical circuits from electrical interference without affecting system function and performance. Typically, filter connectors use ceramic planar arrays for filtering, which may not be appropriate for use in applications that are subject to repeated shock, vibration and temperature extremes.

The planar array design that is currently the industry standard for filter connectors uses a block capacitor with plated through-holes where feed-through contacts are inserted and soldered into place. The planar array filters are ceramic based, and require a reliable electrical joint with the contact through a variety of soldering processes. However, under severe environmental stresses, the ceramic capacitor can become damaged or cracked, resulting in electrical failure. Therefore, costly thermal shock screening and burn-in procedures are required to assure the connector’s electrical performance integrity.

ITT’s new Cannon chip-on-flex (CoF) technology was developed to handle high shock and vibration, extreme temperature fluctuations, and provide a more lightweight solution.

Flexible circuit
Chip-on-Flex designs replace the ceramic planar array block capacitor with a patented, state-of-the-art flexible circuit where individual chip capacitors are surface mounted onto a pad adjacent to the feed-through contact. Since the feed-through contacts are not soldered directly to the capacitor, potential stress points caused by thermal shock and vibration are virtually eliminated.

The result is a very robust filter connector with superior mechanical performance and improved reliability. These CoF filter connectors provide all standard filtering capabilities, including individual isolated pin filtering of high-frequency noise; built-in ground plane barriers in the connector inserts; and filtering at the face of system boxes.

In addition, because the flex circuit is significantly lighter in weight than an array, and as less solder is required for the flex material, a connector weight reduction of up to 15% is achieved for MIL-DTL-38999 configurations. This new CoF filter approach offers the system designer complete flexibility in defining or changing individual circuit capacitance, ground and electromagnetic pulse (EMP) performance during the design/development phase – eliminating any need to retool the ceramic planar array. The CoF design uses readily available flex circuits and devices leading to reduced design/development cycle time and overall production delivery.

CoF technology not only maintains the same performance benefit as traditional ceramic filter capacitors, but it affords ease of customisation for the end users. For instance, EMP protection can be added by substituting a Zener diode in place of a chip capacitor. The user can also easily select and change the cut-in frequency from the performance attenuation curves for each individual circuit
requirement.

Process advantages
There are also significant manufacturing process advantages. Ceramic planar arrays either have to be hand-soldered or have solder rings hand-applied prior to reflow oven soldering, leading to varied solder deposits. In contrast, CoF manufacturing processes eliminate this significant source of process variability through newly-developed error-proof robust solder application process.

ITT’s CoF filter design is available for all standard connector families, including Mil-DTL-38999, Mil-DTL-24308, Mil-C-26482, ARINC 600 and ARINC 404. Customer designs are also easily accommodated.

These connectors have passed MIL-DTL-38999 Series III testing for thermal shock, random vibration, humidity and high altitude DWV. These connectors are ideal for high-reliability military, aerospace and industrial applications including integrated avionics, radio and navigation systems, fire control devices, electronic counter measures, satellite communications and data transmitters.