Optimizing Vibration Isolation of Flex Circuits in Hard Disk Drives

A “flex circuit” is a laminate of polyimide substrate, adhesive, and copper conductors that is used to connect the stationary electronic components in a computer hard disk drive to the rotating arm that positions read/write heads above the disks. The flex circuit’s transverse and longitudinal vibrations couple with the arm, and those motions, although seemingly small, degrade performance during seek operations from one data track to another. The flex circuit and arm mechanism is defined by a number of geometric parameters, and some latitude is available at the design stage for choosing dimensions and angles so as to minimize vibration transmission from the flex circuit to the arm. In this paper, the results of parameter, optimization, and experimental studies are discussed with a view toward improving isolation of the arm from vibration of the flex circuit in one or several modes. Particularly for the mechanism’s odd modes, the flex circuit’s free length and the relative attachment angle between the arm’s centerline and the circuit can each be chosen to significantly reduce vibration transmission. A genetic algorithm was applied to minimize a metric of vibration coupling in several vibration modes, and, in the case study examined, vibration isolation was improved by over 80%.