Thin Glass Substrate Flatness Control for Magnetic Disk Warpage
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Solution Overview
Problem
Magnetic disk glass substrates experience warping and deterioration in flatness due to thermal contraction during heat treatment, leading to instability and poor performance in hard disk drive devices, especially when using high-temperature heat-assisted magnetic recording methods.
Innovation Solution
A glass plate with a thickness less than 0.68 mm and a degree of flatness of 30 μm or less, subjected to specific heat treatment conditions to achieve a thermal contraction rate of 130 ppm or less, and an amount of change in flatness of 10 μm or less, is used to manufacture a magnetic disk glass substrate that suppresses warpage and maintains high flatness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat treatment is performed on the glass substrate at high temperature to enable heat-assisted magnetic recording, then the magnetic recording layer can be formed with suitable properties, but the glass substrate deforms due to thermal contraction
Solution Approach 1:
The glass substrate is subjected to preliminary annealing treatment before magnetic film formation to reduce residual stress and minimize thermal contraction during subsequent high-temperature heat treatment. This preliminary action prepares the substrate to maintain its shape during the critical magnetic recording process.
Solution Approach 2:
The glass transition temperature Tg of the substrate is controlled to be within a specific range (700-850°C) to optimize its thermal stability. By adjusting this material parameter, the substrate can withstand the heat treatment temperature (600-700°C) required for magnetic recording without excessive deformation.
2Ease of manufacture
If the glass substrate is heated to high temperature for heat treatment, then the magnetic film can be properly formed, but thermal contraction causes warping of the glass substrate
Solution Approach 1:
Annealing treatment is performed as a preliminary step before magnetic film deposition to pre-stress the glass substrate. This reduces the substrate's tendency to warp during the subsequent high-temperature magnetic film formation process, maintaining manufacturing precision.
Solution Approach 2:
The glass composition is specifically designed to achieve a glass transition temperature Tg between 700-850°C, which optimizes the balance between heat resistance during magnetic film formation and control of thermal contraction to prevent warping.
3Productivity
If a thin glass substrate is used to increase storage capacity, then more magnetic disks can be mounted, but the substrate becomes more susceptible to warping during heat treatment
Solution Approach 1:
The glass transition temperature Tg is precisely controlled within 700-850°C to enhance the thermal stability of thin substrates. This parameter optimization allows thin glass substrates (0.2-0.6mm) to resist warping during heat treatment while maintaining the thinness required for high storage capacity.
Solution Approach 2:
Pre-annnealing the thin glass substrate before magnetic film formation reduces residual stresses that would otherwise cause warping during heat treatment. This preliminary action enables thin substrates to maintain their flatness and structural integrity throughout the manufacturing process.
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 reduces thermal contraction and maintains the flatness of magnetic disk glass substrates, preventing warpage and ensuring stable operation of magnetic disks even at high temperatures, thereby enhancing the performance and reliability of hard disk drive devices.
Implementation Method 1
When a glass plate is manufactured using any of the above-described methods such as the float method, the glass plate is annealed while being formed
Implementation Method 2
the glass substrate warps during thermal contraction caused by heat treatment performed on the magnetic film
Data Source
AI summary
A glass plate is a rectangular plate having a thickness less than 0.68 mm. A square measurement region having a length of 100 mm per side and cut out from a central region of the glass plate has a degree of flatness of 30 μm or less. When subjected to first heat treatment in which the measurement region is kept at 700° C. for 4 hours and then cooled from 700° C. to 400° C. at a rate of 50° C./hour, the measurement region has a thermal contraction rate of 130 ppm or less. When subjected to second heat treatment in which the measurement region is kept at Tg-160° C. for 60 seconds and then cooled to room temperature in ambient air, where Tg (° C.) represents a glass transition temperature of the glass plate, an amount of change in the degree of flatness of the measurement region is 10 μm or less.