Medical Device Feedthrough Fatigue Characterization

Medtronic feedthroughs are designed to allow electrical current to pass through a device shield while keeping the internal components isolated from the external environment (referred to as hermeticity). These feedthroughs are composed of a metal ferrule, a glass insulator and a conductive pin. It is believed that feedthroughs experience fatigue as a result of manufacturing and in vivo loading conditions. This may result in pin fracture or loss of hermeticity. The high temperature during the glass reflow assembly process effects the mechanical properties of the materials. Thus, assembled feedthroughs must be tested, rather than the as received pin material. In this experiment, a new pin material with an increased strength was characterized using fully reversed bending fatigue tests and compared to the current design material.

It is believed that the feedthroughs operate in a displacement controlled environment due to their relatively small size.  Therefore, samples were cycled to various degrees of bending in order to characterize the relationship between approximate bending angle and cycles to fracture.  Changes to ferrule and glass design are also incorporated such that complete design level changes can be evaluated against existing product.  Mechanical tests and metallurgical cross-sections were also conducted to characterize the incoming pin material, as well as any changes in properties due to manufacturing.