FPC Bond Pad Mesh Reduces Capacitance in Disk Drive HSA
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Solution Overview
Problem
Modern magnetic hard disk drives experience electrical impedance discontinuity at the connection point between flexure bond pads and FPC bond pads, which limits signal bandwidth and data transfer rate, making it impractical to reduce bond pad size to mitigate this issue.
Innovation Solution
The design incorporates internally patterned FPC bond pads with mesh or slotted openings to reduce effective surface area, thereby minimizing electrical capacitance and impedance discontinuity, using anisotropic conductive films for secure and conductive bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If bond pad size is reduced to reduce electrical capacitance and impedance discontinuity, then electrical impedance discontinuity is reduced, but bond pad alignment uncertainty cannot be accommodated
Solution Approach 1:
The bond pad structure is segmented into multiple functional zones: a larger alignment tolerance zone for manufacturing variability and a smaller effective capacitance zone for electrical performance. The mesh pattern segments the conductive area while maintaining overall pad geometry, allowing different regions to serve different purposes.
Solution Approach 2:
Different regions of the bond pad have different electrical properties. The mesh pattern creates areas of varying capacitance density, with the effective capacitance area being smaller than the total geometric area. This local variation in electrical quality allows the pad to accommodate alignment uncertainty while maintaining low impedance discontinuity.
2Manufacturing precision
If bond pad area is increased to accommodate alignment uncertainty, then bond pad alignment is improved, but electrical impedance discontinuity increases
Solution Approach 1:
The bond pad incorporates a mesh pattern that creates a porous-like structure with controlled voids or slots within the conductive material. This reduces the effective surface area available for capacitive coupling while maintaining the overall geometric footprint needed for alignment tolerance. The mesh structure allows electrical connection while minimizing parasitic capacitance.
3Reliability
If FPC bond pads are used to connect flexure bond pads, then electrical connections are established, but electrical impedance discontinuity occurs at the connection point
Solution Approach 1:
The patent changes the electrical parameters of the bond pad by modifying its geometric configuration to a mesh pattern. This alters the capacitance parameter while maintaining the connection function, thereby reducing impedance discontinuity at the FPC-flexure interface without sacrificing connection reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces electrical impedance discontinuity, enhancing signal bandwidth and data transfer rate without compromising bond pad alignment or size, ensuring reliable electrical connections.
Implementation Method 1
using anisotropic conductive films for secure and conductive bonding
Data Source
AI summary
A head stack assembly (HSA) for a disk drive includes an actuator body, at least one actuator arm extending from the actuator body, and a flexible printed circuit (FPC). The FPC may include a FPC conductive layer having a plurality of FPC traces that terminate at respective ones of a plurality of electrically conductive FPC bond pads. The FPC may include a metallic FPC stiffener layer having a surface that underlies and faces the FPC bond pads. The FPC stiffener layer surface may include a plurality of recessions having a depth of at least 25 microns. A FPC dielectric layer may be disposed between the FPC conductive layer and the metallic FPC stiffener layer. One or more of the plurality of FPC bond pads may be internally patterned to define a FPC bond pad mesh with a plurality of openings therethrough.