Magnetic Disk Substrate Surface Roughness Impact Resistance
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Solution Overview
Problem
Thinned magnetic disk substrates in hard disk devices are prone to significant vibration upon external impact, leading to collisions with external members like ramps, resulting in defects such as scratches and particle generation, which existing technologies fail to adequately address, especially when the gap between the disk and ramp is narrowed.
Innovation Solution
A magnetic disk substrate with controlled surface roughness on its fixed portions, where the root mean square deviation of surface roughness (Rq) is between 0.01 to 0.44 μm, effectively reducing displacement and enhancing impact resistance, even when the substrate is thinned to 0.5 mm or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the magnetic disk substrate is thinned to increase the number of loaded disks, then the device capacity increases, but the impact resistance deteriorates and vibration increases
Solution Approach 1:
The invention applies different surface roughness characteristics to different regions of the magnetic disk substrate. The fixed portion (center region) has a controlled surface roughness Rq of 0.01 to 0.05 μm to reduce impact transmission, while the outer circumferential portion maintains sufficient roughness for magnetic layer formation. This local differentiation allows the thinned substrate to resist impact while maintaining functionality.
Solution Approach 2:
The invention changes the surface roughness parameter (Rq value) of the fixed portion to a specific range (0.01 to 0.05 μm) to optimize impact resistance. By controlling this physical parameter, the substrate achieves reduced vibration and improved reliability when thinned to 0.5 mm or less, enabling higher disk capacity without compromising durability.
2Volume of moving object
If the gap between the magnetic disk and ramp is narrowed to increase disk density, then the device size is reduced, but the risk of collision and defects increases
Solution Approach 1:
The invention creates a localized low-roughness region (Rq: 0.01 to 0.05 μm) at the fixed portion of the substrate that acts as a vibration-damping zone. This local quality modification reduces the amplitude of substrate vibration during impact, allowing narrower gaps between disks and ramps without increasing collision risk, thus enabling compact device design.
Solution Approach 2:
The controlled surface roughness at the fixed portion serves as a pre-established cushioning mechanism against impact. By preparing this low-roughness region beforehand, the substrate is pre-conditioned to absorb and dissipate impact energy, reducing vibration amplitude before collision can occur, thereby enabling safer narrowing of the disk-ramp gap.
3Reliability
If the surface roughness is reduced to minimize vibration, then the impact resistance improves, but the magnetic layer formation may be affected
Solution Approach 1:
The invention divides the substrate surface into functionally distinct regions: the fixed portion (center) with low surface roughness (Rq: 0.01 to 0.05 μm) for vibration suppression, and the outer circumferential portion with higher roughness suitable for magnetic layer formation. This segmentation allows each region to optimize its function without compromising the other.
Solution Approach 2:
The invention applies different surface quality characteristics to different locations on the substrate. The fixed portion has precisely controlled low roughness (Rq: 0.01 to 0.05 μm) to minimize vibration, while the outer regions maintain adequate roughness for magnetic layer adhesion. This local quality differentiation resolves the conflict between vibration suppression and manufacturing precision.
Data Source
AI summary
A magnetic disk substrate having a pair of front and back principal surfaces, containing fixed portions that are in contact with fixing jigs when the magnetic disk substrate configured as a magnetic disk is incorporated in a hard disk device on the respective front and back principal surfaces, wherein a root mean square deviation Rq of surface roughnesses of the fixed portions on the respective front and back principal surfaces is from 0.01 to 0.44 μm.; anda magnetic disk using the same.