Thin Magnetic Disk Substrate Flatness Under Thermal Shock
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Solution Overview
Problem
Conventional magnetic disk substrates with reduced thickness face challenges in maintaining planar level and long-term reliability due to increased physical errors, such as head crashes, which are exacerbated by thermal shock in actual use environments.
Innovation Solution
A substrate for magnetic disks with a thickness of less than 0.50 mm and an outer diameter of 95 mm or more, made of materials like aluminum alloy or glass, is subjected to a thermal shock test and polished to achieve a planar level of 12 μm or less through a process involving rough and fine polishing, with a dummy polishing step to adjust polishing pad surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the substrate thickness is reduced to increase hard disk capacity, then the storage density is improved, but the planar level deteriorates and long-term reliability decreases
Solution Approach 1:
The patent applies parameter changes by controlling the planar level within a specific range (PV 15μm or less, preferably PV 12μm or less) after thermal shock testing. This quantitative parameter control resolves the contradiction by establishing a threshold that ensures reliability even with thin substrates (less than 0.50mm thickness), enabling high storage capacity while maintaining long-term operational stability.
2Quantity of substance
If the substrate thickness is reduced to increase hard disk capacity, then the storage density is improved, but the planar level after thermal shock deteriorates
Solution Approach 1:
The patent applies preliminary action by performing thermal shock testing during the manufacturing process to pre-establish the planar level characteristics before actual use. substrates are subjected to thermal shock cycles (heating to 120°C and cooling to -40°C repeatedly) during production, allowing manufacturers to select and process only those substrates that maintain PV 15μm or less after thermal shock, thereby ensuring manufacturing precision is achieved before the product reaches the customer.
3Manufacturing precision
If conventional flattening techniques are applied to improve planar level, then the surface flatness is improved, but long-term reliability in actual use environment remains insufficient
Solution Approach 1:
The patent converts the harmful effect of thermal shock into a beneficial testing mechanism. By subjecting substrates to thermal shock cycles during manufacturing and using the resulting planar level degradation as a selection criterion (PV 15μm or less after thermal shock), the patent transforms what would normally be a reliability problem into a quality control tool, ensuring that only substrates capable of maintaining precision under thermal stress are selected for production.
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 substrate maintains an improved planar level and enhances long-term reliability by withstanding thermal shock, addressing the issues of planar degradation and physical errors in thin-walled disks.
Implementation Method 1
a rough polishing step of roughly polishing both surfaces of a disk-shaped blank substrate; and a fine polishing step of finely polishing both the surfaces of the blank substrate subjected to rough polishing
Implementation Method 2
a thermal shock test performed by repeating a cycle of heating the substrate at 120° C. for 30 minutes and subsequently cooling the substrate at −40° C. for 30 minutes for 200 times
Data Source
AI summary
The present invention intends to provide a substrate for a magnetic disk and a method for manufacturing same, and a magnetic disk capable of holding high flatness after long-term use despite being thin, coping with a high capacity of hard disk, and improving long-term reliability thereof. In the substrate according to the present invention, when a process for heating a substrate at 120° C. for 30 minutes and then cooling the substrate at −40° C. for 30 minutes is defined as one cycle, the flatness PV of a surface of the substrate measured at 25° C. after a thermal impact test in which the cycle is repeatedly performed 200 times is not more than 12 μm. The present invention further encompasses a magnetic disk having a similar flatness PV under the same conditions. The present invention still further encompasses a method for manufacturing the substrate for a magnetic disk.