Degradation Analysis of Flexible Film Cables in an Automotive Environment

Automobiles have a high degree of mechanical and electrical complexity. However, product complexity has the accompanying effect of requiring high levels of design and process oversight. The net result is a product creation process which is prone to creating failures. These failures typically have their origin in an overall lack of complete understanding of the system in terms of materials, geometries and energy flows. Despite all of the engineering intentions, failures are inevitable, common, and must be dealt with accordingly. In the worst case, if a failure manifests itself into an observable failure the customer may have a negative experience. Therefore, it is imperative that design engineers, suppliers along with reliability professionals be able to assess the design risk. One approach to assess risk is the use of degradation analysis. Degradation analysis often provides more information than failure time data for assessing reliability and predicting the remnant life of a system. In general, degradation is the reduction in performance over time leading to an observed failure. Many failures may be traced to an underlying degradation process. For example, one failure mode associated with Flexible Film Cable (FFC) is electrical short between circuits due to migration. Under certain conditions (e.g. elevated temperatures) the ribbon material becomes pliable and if the cable is under stress the encased wires may begin to migrate towards one another ultimately resulting in an electrically shorted condition. This type of situation is a kind of stochastic process; therefore, it could be modelled in several approaches. This paper presents the degradation analysis approach as applied to the FFC in an attempt to identify the merits, limitation, and applications of degradation analysis in generating system understanding by which to make informed decisions.