Suspension Substrate Warpage Control via Hygroscopic Expansion Matching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Substrates for suspension in hard disk drives with decreased rigidity tend to warp due to differences in thermal and hygroscopic expansion coefficients between metallic and insulating layers, leading to inadequate warpage reduction and production yields.
Innovation Solution
A substrate design with a metallic substrate, an insulating layer, and a cover layer, where the coefficients of hygroscopic expansion of the insulating and cover layers are within specific ranges (0-30×10−6/% RH) and their difference is minimized, using different or the same non-photosensitive materials, such as polyimides, to control warpage and rigidity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the metallic substrate percentage is decreased to reduce rigidity, then the substrate can access smaller disks more effectively, but the substrate tends to warp due to thermal and hygroscopic expansion differences
Solution Approach 1:
The patent applies parameter changes by carefully selecting materials with specific coefficients of thermal expansion and hygroscopic expansion. The insulating layer material is chosen to have a coefficient of thermal expansion within 10×10^-6/℃ to 30×10^-6/℃ and a coefficient of hygroscopic expansion within 0 to 30×10^-6/% RH, matching these parameters to the metallic substrate to minimize expansion differences and prevent warping while maintaining reduced rigidity for smaller disk access
2Shape
If the coefficient of thermal expansion difference between metallic substrate and insulating layer is reduced to minimize warping, then warpage is partially improved, but warpage reduction remains inadequate when metallic substrate percentage is low
Solution Approach 1:
The patent extends parameter changes to include both thermal and hygroscopic expansion coefficients. By controlling the insulating layer material to have a coefficient of hygroscopic expansion within 0 to 30×10^-6/% RH in addition to thermal expansion control, the patent addresses warping from both thermal and moisture-related expansion, providing adequate warpage reduction even when metallic substrate percentage is decreased
Solution Approach 2:
The patent employs composite materials by selecting an insulating layer material that simultaneously satisfies multiple expansion parameter requirements. This composite approach combines appropriate thermal and hygroscopic expansion properties in a single material system, enabling comprehensive warpage control through material composition rather than relying solely on thermal expansion matching
3Adaptability or versatility
If different materials are used for insulating layer and cover layer, then material selection flexibility increases, but production complexity and yield control become more difficult
Solution Approach 1:
The patent applies parameter changes by establishing specific numerical ranges for expansion coefficients that guide material selection. By defining clear parameter thresholds (thermal expansion: 10×10^-6/℃ to 30×10^-6/℃, hygroscopic expansion: 0 to 30×10^-6/% RH), the patent simplifies material selection and quality control, making production more manageable while maintaining flexibility in choosing materials that meet these specifications
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 warps minimally even with decreased rigidity, maintaining low hygroscopic and thermal expansion, facilitating high-yield production and reduced warpage, while allowing for easier material selection and process control.
Implementation Method 1
the coefficients of hygroscopic expansion of the insulating-layer-forming material and the cover-layer-forming material are in the range between 0×10−6 to 30×10−6/% RH, and, moreover, the difference between the coefficients of hygroscopic expansion of the two materials is in the range between 0×10−6 to 5×10−6/% RH
Implementation Method 2
the difference between the coefficients of thermal expansion of the insulating layer and that of the cover layer is 10×10−6/℃ or less
Data Source
AI summary
A substrate for suspension comprises a metallic substrate, an insulating layer formed on the metallic substrate, a conductor layer formed on the insulating layer, and a cover layer covering the conductor layer. The insulating layer and the cover layer are formed from different materials, whose coefficients of hygroscopic expansion are in the range between 3×10−6/% RH and 30×10−6/% RH. The difference between the coefficients of hygroscopic expansion of the two materials is 5×10−6/% RH or less.