Challenge: Lightweight reliable electrical interconnects that can withstand the rigors of outer space travel and perform without failure 40 million miles away
Solution: Rigid Flex circuits made with DuPont™ Pyralux® AP copper clad laminate and DuPont™ Pyralux® LF coverlay and adhesive
The initial Mars Pathfinder mission demonstrated that unmanned robotic exploration of the surface of Mars was indeed possible. The MARS Rover Project, Spirit and Opportunity, goal was much more aggressive: deliver two larger self contained rovers to the surface of Mars that had significantly greater mobility, analytical instrumentation, optics and data communication equipment than was ever before assembled in one package. Reliable interconnection of all these mechanical and electrical devices within the size and weight limitations typically required in a space mission would be a formidable task. On top of the physical limitations, these systems would be expected to withstand a high G force landing and remain functional at surface temperatures that would range from -120°C to + 22°C.
Materials Selected and Why
Rigid flex circuits have a long history of reliably interconnecting instrumentation in space and avionics applications. Mechanical connectors can experience intermittent or total loss of signal when exposed to excessive temperature cycling, vibration or shock. The integrated through-hole connections in rigid-flex designs eliminate this potential source of failure. Rigid flex circuits have been demonstrated to both reduce weight and increase reliability when compared to designs employing wire harnesses and connectors. It was estimated that the rigid flex approach reduced the volume that would have been required by round wires, cables and connectors by 60 to 70%.
The premier copper clad laminate for rigid-flex applications is Pyralux® AP . Pyralux® AP is an all-polyimide laminate with no traditional adhesive layer. It has a CTE of 106 ppm/C in the z-axis. Most adhesive systems are four times this number. Furthermore, the Tg of Pyralux® AP is 220°C. The combination of these two properties makes Pyralux® AP an ideal choice for highly reliable plated through holes. In addition, since there is no added layer of adhesive to bond the copper to the base dielectric, on an equal area basis Pyralux® AP weighs less that an equivalent adhesive based clad.
Where adhesive is needed to secure the coverlay to the flex sections or to bond multi-layer flex circuits together, Pyralux® LF is also the material of choice. Its acrylic chemistry base means that is has both superior initial peel strength and can take multiple temperature excursions without degrading. Pyralux® LF has been the preferred adhesive of choice for most high-end avionics and aerospace flex applications for the past three decades.
The MARS Rovers, Spirit and Opportunity have continued to perform well beyond JPL and NASA’s wildest expectations. To date they have sent back over 68,000 images and have operated for more than 450 "sols" (Martian days) longer than was originally planned. They are both still operating today collecting and sending data back to earth.