Magnetic-Disk Glass Substrate Edge Polishing for Foreign Matter Control
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Solution Overview
Problem
The production of magnetic-disk glass substrates is hindered by the occurrence of fine foreign matter caused by glass components, leading to issues like head crash and thermal asperity, which is attributed to damage during polishing processes due to unevenness in the outer circumferential edge surface.
Innovation Solution
A disk-shaped glass substrate with a roundness of 1.3 μm or less and specific surface roughness and peak count ratio properties is developed, achieved through edge surface polishing and main surface polishing processes, to prevent damage and foreign matter formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If edge surface polishing is performed to reduce unevenness, then foreign matter occurrence is suppressed, but manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by performing edge surface polishing before main surface polishing. The edge surface is pre-polished to reduce unevenness and prevent damage during subsequent main surface polishing, thereby suppressing foreign matter occurrence. This sequential approach addresses the root cause before the main polishing process occurs.
Solution Approach 2:
The patent segments the polishing process into two distinct stages: edge surface polishing and main surface polishing. By dividing the overall polishing operation into separate sequential steps with different objectives and parameters, the process achieves better control over surface quality and foreign matter prevention while maintaining manufacturing feasibility.
2Reliability
If roundness is reduced to 1.3 μm or less, then magnetic head stability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies preliminary action by performing edge surface polishing before main surface polishing. The edge surface is pre-polished to reduce unevenness and prevent damage during subsequent main surface polishing, thereby suppressing foreign matter occurrence. This sequential approach addresses the root cause before the main polishing process occurs.
Solution Approach 2:
The patent segments the polishing process into two distinct stages: edge surface polishing and main surface polishing. By dividing the overall polishing operation into separate sequential steps with different objectives and parameters, the process achieves better control over surface quality and foreign matter prevention while maintaining manufacturing feasibility.
3Shape
If peak count ratio is reduced to 0.2 or less, then surface smoothness is improved, but process control complexity increases
Solution Approach 1:
The patent applies feedback by measuring the peak count ratio of the outer circumferential outline and using this measurement to control the edge surface polishing process. The peak count ratio serves as a quantitative feedback parameter that guides the polishing operation to achieve the desired surface smoothness while preventing excessive material removal or damage.
4Productivity
If main surface polishing is performed on substrates with uneven edge surfaces, then production efficiency is maintained, but foreign matter and damage occur
Solution Approach 1:
The patent applies preliminary action by performing edge surface polishing before main surface polishing. The edge surface is pre-polished to reduce unevenness and prevent damage during subsequent main surface polishing, thereby suppressing foreign matter occurrence. This sequential approach addresses the root cause before the main polishing process occurs.
Solution Approach 2:
The patent segments the polishing process into two distinct stages: edge surface polishing and main surface polishing. By dividing the overall polishing operation into separate sequential steps with different objectives and parameters, the process achieves better control over surface quality and foreign matter prevention while maintaining manufacturing feasibility.
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
The solution effectively suppresses the occurrence of foreign matter, ensuring stable magnetic head operation and preventing issues like head crash and thermal asperity, as demonstrated by the production of magnetic disks with no detected damage or foreign matter under microscopic examination.
Implementation Method 1
edge surface polishing and main surface polishing processes
Data Source
AI summary
A disk-shaped glass substrate for a magnetic-disk glass substrate includes an outer circumference having a roundness of 1.3 μm or less. A first reference circle is obtained with a least squares method from a first outline corresponding to a shape of a lap around the outer circumference. A second reference circle is obtained with a least squares method from a second outline obtained by performing low-pass filtering using a period in which the number of peaks per lap is 150 as a cut-off value on the first outline. A ratio of the second peak count value defined by the number of peaks of the second outline that project outward in a radial direction from the second reference circle to the first peak count value defined by the number of peaks of the first outline that project outward in a radial direction from the first reference circle is 0.2 or less.