Vibration of Flex Circuits in Hard Disk Drives

[+] Author and Article Information
J. A. Wickert

Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213

J. Vib. Acoust 125(3), 335-342 (Jun 18, 2003) (8 pages) doi:10.1115/1.1547661 History: Received May 01, 2002; Revised October 01, 2002; Online June 18, 2003
Copyright © 2003 by ASME
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Photograph depicting certain mechanical components within a hard disk drive used for computer data storage
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Schematic of the equilibrium and vibration model for the arm and flex circuit mechanism
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(a) Brightfield and (b) differential interference contrast micrographs of flex circuit cross-sections. The images depict the construction morphology and the thicknesses of the polyimide, conductor, and adhesive layers.
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Predicted (–) and measured shapes of the flex circuit in equilibrium with attachment to the arm and electronics block, and in its natural state. The shapes extracted from photographs of the circuit in the two states are denoted by the (○) and (•) data points, respectively.
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Equilibrium tension and shear force along the circuit’s arc length
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Variation of the flex circuit’s static shape for arm positions which range between the disk’s outer and inner diameters. For each arm position, the locations of the circuit’s endpoints are denoted by (○).
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Predicted (–) and measured (○) dependencies of the static restoring moment for arm positions between the disk’s outer and inner diameters
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Flex circuit equilibrium shapes predicted for free length’s which range between 70% and 130% of the nominal value in Table 1
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First six vibration modes (–) shown superposed on the equilibrium shape ([[dashed_line]]). Each element of the figure is annotated with the predicted natural frequency and displacement ratio η.
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Test stand used for measuring flex circuit transient responses and natural frequencies. A 90 deg prism directs the target beam from the laser head to the flex circuit. A small patch of retroreflective tape (not visible in the photograph) was placed on the circuit to reduce measurement sensitivity to misalignment and rotation of the circuit during vibration.
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Measured spectrum and natural frequencies of one disk drive’s flex circuit in modes two, three, and four
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Ring-down of a flex circuit in its second mode, which for this disk drive was placed at 332 Hz. The damping ratio is 1.1%.
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Transient response in the arm and flex circuit’s 3.08 Hz fundamental mode following an impact
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Dependence of the natural frequencies in modes two through six on the flex circuit’s free length
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Dependence of the displacement ratios η in modes two through six on the flex circuit’s free length




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