Hard Disk Drive Suspension PSA Stability via Hygroscopic Compensation
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Solution Overview
Problem
Hard disk drive suspensions are sensitive to pitch static attitude (PSA) changes caused by variations in humidity and temperature, leading to performance issues and potential failure due to hygrothermal effects from hygroscopic materials like polyimide and non-hygroscopic materials like stainless steel and copper.
Innovation Solution
The introduction of non-hygroscopic or hygroscopic material patches on the flexible circuit and gimbal outrigger arms, along with selective removal or adjustment of layers, to counteract bending effects and maintain a stable PSA, including stainless steel islands on the suspended portion and polyimide patches on the outrigger arms, ensuring opposite bending directions to cancel out humidity-induced changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hygroscopic materials (polyimide, coverlayer) are used in the flexible circuit, then the suspension provides necessary insulation and protection, but the PSA changes due to humidity-induced expansion and contraction
Solution Approach 1:
The patent applies local quality by adding non-hygroscopic material patches at specific locations on the flexible circuit and gimbal outrigger arms. These patches are strategically positioned to counteract the expansion of hygroscopic materials in specific regions, creating localized compensation zones that balance the overall PSA changes.
Solution Approach 2:
The patent changes the physical parameters of the suspension structure by introducing materials with different hygroscopic properties. The non-hygroscopic patches have different expansion coefficients compared to the hygroscopic polyimide and coverlayer, creating a parameter imbalance that compensates for humidity-induced PSA changes.
2Stability of the object's composition
If non-hygroscopic materials (stainless steel, copper) are used in the flexible circuit, then the structural stability is maintained, but the insulating and protective functions are reduced
Solution Approach 1:
The patent uses composite materials by combining non-hygroscopic materials (stainless steel patches, copper signal traces) with hygroscopic materials (polyimide insulating layer, coverlayer). This composite structure allows the suspension to benefit from both the structural stability of non-hygroscopic materials and the insulating/pro protective properties of hygroscopic materials.
3Ease of manufacture
If the flexible circuit is made without stainless steel support layer in suspended portions, then the copper signal traces can be thinner and softer, but the resistance to humidity-induced bowing increases
Solution Approach 1:
The patent applies the counterweight principle by adding non-hygroscopic material patches on the suspended portions of the flexible circuit. These patches act as counterweights to the expansion forces generated by the hygroscopic materials, creating a balancing effect that reduces net bowing while allowing the copper traces to remain thin and soft.
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 significantly reduces net bending and maintains a stable PSA, improving resistance to environmental changes, with PSA changes minimized to within 10% to 20% accuracy, effectively addressing hygrothermal effects and maintaining disk drive performance.
Implementation Method 1
The materials used for the insulating layer, which is typically polyimide, and for the coverlayer, are typically hygroscopic, meaning that they absorb water from the atmosphere. When those materials absorb water from the atmosphere they expand
Implementation Method 2
In contrast, the metal support layer of the suspension, which is typically stainless steel, and to which parts of the circuit are laminated or otherwise adhered, is non-hygroscopic. The copper signal traces are also non-hygroscopic. When a suspension is exposed to increasing humidity, therefore, the polyimide and the coverlayer expand, while the stainless steel support layer to which it is adhered and the copper signal traces do not expand
Implementation Method 3
The copper layer 24 is thinner, narrower, and softer than stainless steel layer 20, and hence presents less resistance to expansion than does stainless steel layer 20
Data Source
AI summary
In a disk drive suspension circuit, in order to improve stability of the stable pitch static attitude (PSA) over changes in humidity, the suspended portion of the flexible circuit and/or the gimbal support arm are modified to change their response(s) to humidity. In one embodiment, hygroscopic material such as the material of the insulating layer are added to the stainless steel gimbal support arm, so that in response to humidity it bends in the opposite direction as the suspended portion of the circuit. In another embodiment, additional hygroscopic material is added to the circuit, and/or the polyimide insulating layer or the coverlayer are selectively removed, so that the net bend in the suspended portion of the circuit over humidity is reduced, ideally to a condition of zero or close to zero net bending.