High Performance / Reliable Automatic Transmissions rely on Flex Circuit Cables for a better Engineered Interconnect
Challenge: Reduce Production and Assembly Costs without Compromising Reliability
Solution: DuPont™ Pyralux® LF & FR - Acrylic Adhesive Based Flex Circuit Cable Assemblies Withstand the Harsh Environment of an Automotive Drivetrain
The automotive industry is under constant pressure to reduce production & assembly costs and to increase overall productivity and reliability. It is an on-going challenge to find ways to simplify complex designs especially when they are required to function in the very harsh environments of the automotive world. This is particularly true in electrical interconnects. Electronic systems and controls are becoming a greater percentage of the overall cost of the car and are more and more the focus of reengineering efforts.
In this case a complex discrete wire cable harness for an automatic transmission gear box control was both difficult to build and akward to assemble. However, it was quite reliable so any alternative approach in addition to being less expensive would have to survive a difficult performance requirement: work flawlessly while continuously immersed in automotive transmission oil at 120°C for the life of the car.
Materials Selected and Why
A flex circuit cable was proposed as an alternative to the more complex individual wire / cable assembly. The use of a flex circuit eliminates the need to bundle a number of individual wires together to form a cable. Routings are determined by a single artwork rather than by individual wires. Maintaining the accuracy of the design is assured by semiautomatic processing from start to finish. Clearly these "pre-fabricated" cables would be easier to build, would reduce assembly costs and eliminate rework but would flex circuits survive the performance and reliability requirements?
DuPont™ Pyralux® FR and Pyralux® LF acrylic adhesive based flexible laminates were chosen as the preferred material. In general acrylic adhesives offer superior resistance to thermal degradation than epoxy adhesives which are typically used in flex circuit applications.
The initial design was qualified by exposing the circuit to 150C oil at 2 atmospheres for 90 days. Pyralux® acrylic laminate passed this qualification test with flying colors. The flex cable was internally qualified as a replacement for the wire harness and was installed in vehicles. Its actual performance was monitored over time and during these field trials it performed flawlessly. Today, more than 8 years after initial qualification and adoption, Pyralux® circuits are still being fabricated and installed in this application. More than 450,000 circuits / year have been produced and there has not been a field failure reported that involved a material performance issue.
Other automotive system suppliers have noticed this level of reliability and have started to take advantage of the design options flex circuits provide. Pyralux® acrylic flex circuits are now being used in multiple transmission controls, fuel pumps and engine controls systems for a wide variety of automotive manufacturers.
As a result of this success, Pyralux® is finding its way into a variety of other automotive sensor and electrical interconnect circuits where cost and reliability are both critical success factors.
One recent example is DaimlerChrysler, who is currently utlizing a Pyralux® laminated flexible printed circuit board that enables communications between the magnetic values, sensors and floats, the gearbox connector, and the electronics. For more information, click here.