Magnetic Disk Glass Substrate Surface Roughness Control
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Solution Overview
Problem
Magnetic-disk glass substrates experience issues like head crash and thermal asperity due to colloidal silica microparticles remaining on the surface, despite having sufficiently small surface roughness, as conventional roughness indices do not account for deep grooves where these particles can be trapped.
Innovation Solution
The magnetic-disk glass substrate is designed with specific surface properties, including an arithmetic average roughness (Ra) of 0.015 μm or less and a bearing factor of 95% or more for the roughness cross-sectional area at 60%, reducing the likelihood of colloidal silica microparticles attaching to the side wall and chamfered surfaces, which minimizes the formation of deep grooves and subsequent particle trapping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the surface roughness of the magnetic-disk glass substrate is made sufficiently small to prevent head collision, then the smoothness of the main surface is improved, but colloidal silica microparticles become trapped in deep grooves on side wall and chamfered surfaces, causing head crash and thermal asperity
Solution Approach 1:
The patent applies different surface roughness requirements to different parts of the glass substrate. The main surface is polished to extremely high smoothness (Ra ≤ 0.003 μm) to prevent head collision, while the side wall surfaces and chamfered surfaces are controlled to have moderate roughness (Ra ≤ 0.015 μm) with specific bearing factor characteristics that prevent particle trapping. This localized differentiation of surface quality resolves the contradiction by optimizing each region for its specific function.
Solution Approach 2:
The patent introduces new surface characterization parameters beyond conventional roughness measurements. Specifically, it uses the bearing factor of the roughness cross-sectional area at 60% roughness percentage as a critical parameter to control the geometry of grooves on side wall and chamfered surfaces. By controlling this parameter to be 95% or more, the patent ensures that deep grooves that could trap particles are minimized, while maintaining the smoothness needed to prevent head collision.
2Ease of manufacture
If conventional surface roughness control methods are used on side wall and chamfered surfaces, then the manufacturing process is simple, but deep grooves are formed that trap colloidal silica microparticles
Solution Approach 1:
The patent changes the control parameters for surface polishing from conventional roughness measurements alone to a composite approach that includes the bearing factor of the roughness cross-sectional area at 60% roughness percentage. This parameter change transforms the polishing process to specifically control groove geometry, preventing particle trapping while maintaining manufacturing feasibility through standardized polishing procedures.
Solution Approach 2:
The patent replaces reliance on purely mechanical polishing parameters with a more sophisticated surface characterization and control system. By using bearing factor analysis of roughness cross-sectional areas, the patent substitutes simple roughness threshold control with a more advanced parameter that directly correlates with particle trapping prevention, thereby improving the effectiveness of the mechanical polishing process.
Data Source
AI summary
A magnetic-disk glass substrate of the present invention includes a pair of main surfaces, a side wall surface, and a chamfered surface between the main surfaces and the side wall surface. Regarding surface properties of at least one of the side wall surface and the chamfered surface of the glass substrate, an arithmetic average roughness (Ra) is 0.015 μm or less, and a bearing factor of a roughness cross-sectional area when a roughness percentage is 60% is 95% or more in a bearing curve of a roughness cross-sectional area.