Magnetic Disk Substrate Offset Portion for Outer Peripheral Flatness
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Solution Overview
Problem
The outer peripheral portion of magnetic disks requires high flatness to prevent fly stiction and head crash failures, especially at high rotational speeds, due to increased linear velocity and uneven surface disturbances, which conventional polishing methods often fail to achieve consistently.
Innovation Solution
A magnetic disk substrate with a disk-shaped structure featuring a generally flat main surface, a chamfered face, and an offset portion at the periphery, where the offset is uniformly distributed in the circumferential direction, ensuring that the raised or lowered shape is approximately the same height across the substrate, thereby stabilizing the magnetic head's flight and preventing contact with the disk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional polishing methods are used on glass substrates, then manufacturing process is simple, but the flatness of outer peripheral portion cannot be maintained at high rotational speeds
Solution Approach 1:
The patent applies different treatment to different regions of the substrate surface. Specifically, the outer peripheral portion (within 3mm from the end face) receives special attention through controlled polishing parameters to achieve uniform flatness, while the central region maintains conventional polishing. This localized quality control resolves the contradiction by focusing manufacturing precision where it is most critical for high-speed operation without unnecessarily complicating the overall process.
Solution Approach 2:
The patent changes polishing parameters (pressure, speed, duration) based on the radial position from the substrate center. By adjusting these parameters progressively from the center toward the periphery, the method achieves uniform flatness in the critical outer region while maintaining manufacturing efficiency. This parameter optimization resolves the contradiction between precision and ease of manufacture.
2Volume of moving object
If substrate size is reduced for mobile devices, then device portability improves, but allowable dimensional error decreases requiring more accurate shape processing
Solution Approach 1:
The patent adjusts polishing parameters based on substrate size and rotational speed requirements. For smaller substrates used in mobile devices, the method optimizes pressure and duration parameters to achieve the required dimensional accuracy within tighter tolerances. This parameter adaptation resolves the contradiction by maintaining high precision requirements for small substrates without making the process unmanageable.
3Quantity of substance
If magnetic head flying height is reduced to increase recording density, then recording capacity improves, but fly stiction failure and head crash risk increase
Solution Approach 1:
The patent ensures that the outer peripheral portion of the substrate, where the magnetic head operates at lowest flying height during high-density recording, has uniformly controlled flatness. By removing local irregularities and protrusions in this critical region through targeted polishing, the method reduces the risk of head contact and stiction failures, thus resolving the contradiction between high recording density and head crash resistance.
Data Source
AI summary
A magnetic disk substrate having a flat main surface, an end face, and a chamfered face formed between the main surface and the end face. The substrate has an offset portion, present on the main surface within a range of 92.0 to 97.0% in a radial direction from a center of the substrate. A distance from the center of the substrate to the end face of the substrate in a radial direction is 100%, the offset portion being raised or lowered with respect to a virtual straight line connecting two points on the main surface, set at positions of 92.0% and 97.0%. A maximum distance from the virtual straight line to the offset portion in a direction perpendicular to the virtual straight line is a “maximum offset value.”