Flex Circuits Fit Where Cables Cannot

Flex Circuits

Flex printed circuits can provide several obvious advantages over conventional ribbon cables in certain applications. For example, a flex circuit can span between a board and a connector on a bulkhead several inches away at a right angle in the same plane as the board. That’s not feasible with a ribbon cable.

Flex connections have mechanical advantages over conventional ribbon cables in various applications but in some cases, they also have better chemistry.

A flex circuit can be formed in complex shapes in three dimensions with branches to multiple connectors, which would be impossible to achieve with a ribbon cable. Moreover, flex circuits can be interfaced with rigid boards without the relatively tall and bulky connectors flat cables require, or in the case of rigid-flex construction, they can be integral with the boards and eliminate external connectors altogether. Furthermore, the conductor density of flex circuits can far exceed that of ribbon cables.

Flex Circuits’ Advantages

There are some subtle advantages of flex circuits versus conventional ribbon cables beyond the many clear distinctions. One of the materials commonly used for flex circuits, Kapton, has extremely low outgassing in ultra-high-vacuum environments, such as space. Though Kapton-insulated ribbon cables are available, they have a limited number of conductors and cannot be routed at angles in tight confines.

Ribbon cables insulated with Teflon and other plastic materials outgas fluorine or reactive compounds when subjected to high vacuums, which can attack electronics in closed containers if care is not taken to completely vent the gases.

A flex-based connection solves tough routing challenges between this tiny navigation device for satellites and its enclosure.
A flex-based connection solves tough routing challenges between this tiny navigation device for satellites and its enclosure.

A Kapton Flex Circuit

Sinclair Interplanetary incorporates a Kapton Class 3 flex circuit fabricated by Sierra Circuits in optical navigation devices the company manufactures for use in small satellites. The nine-conductor flex circuit links a D-type connector, which secures to the device enclosure, with pins on the rigid device board that carry telemetry data, commands, and power.

The flex circuit in this case is swaged to the pins on the six-layer rigid board, which is about the size of a credit card. It sweeps the conductors upward and at a right angle from the pins on route to the connector and ensures the connector is mechanically isolated from the board. The assembly can withstand more than 17.9 gRMS vibration. Sinclair Interplanetary star trackers are aboard several small satellites scheduled for launch in November and December 2013 for scientific and commercial missions.

Sinclair is one of several Sierra customers who manufacture components for small satellites or build the complete satellites. Small satellites—some of them little larger than a shoebox—can perform very complex missions rivaling those accomplished by spacecraft costing dozens of times more. Sierra Circuits also manufactures PCBs for companies that build those large spacecraft.

Want to learn more about Sierra Circuits’ flex and rigid-flex capabilities? Head on over to our flex and rigid-flex product pages!
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