Doubly Thick Flying Leads for Disk Drive Flexure Strength
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Solution Overview
Problem
Fragile unsupported flying leads in disk drive suspensions are prone to damage during assembly, testing, and rework, especially with the reduction in copper conductor layer thickness from 12 μm to 7 μm, making rework more challenging due to lack of mechanical strength.
Innovation Solution
A multi-layer flexure structure is developed with stacked conductors, where a first signal conductor is electrodeposited on a stainless steel support with a polyimide insulating layer, and a second conductor is added with copper plating on both supported and unsupported portions, followed by etching to create doubly thick flying leads without a support layer, enhancing mechanical strength while maintaining flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If copper conductor layer thickness is reduced from 12 μm to 7 μm, then manufacturing precision and flexibility are improved, but mechanical strength and reliability deteriorate
Solution Approach 1:
The patent applies local quality by creating different conductor thicknesses in different regions: the flying lead portion has double the thickness (12-14 μm) compared to the standard conductor layers (7 μm). This is achieved by depositing an additional copper layer specifically on the flying lead portion, providing enhanced mechanical strength where needed while maintaining thin conductors elsewhere for flexibility and precision.
Solution Approach 2:
The patent segments the conductor structure into different thickness regions: standard thickness sections for the suspension circuit and doubled thickness sections for the flying leads. This segmentation allows each region to have optimized properties - the thin sections provide flexibility for suspension movement while the thick sections provide strength for handling and rework.
2Ease of operation
If flying leads are made thinner to maintain flexibility, then ease of operation is improved, but strength and resistance to damage deteriorate
Solution Approach 1:
The flying lead portion is locally reinforced with an additional copper layer, creating a region of double thickness (12-14 μm) compared to the standard 7 μm conductors. This local quality enhancement provides the necessary mechanical strength for handling and rework while the overall flying lead structure remains thin enough to maintain flexibility for suspension movement.
3Reliability
If flying leads are made thicker to improve strength, then reliability is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent segments the conductor deposition process into sequential steps: first depositing the standard 7 μm copper layers, then selectively depositing an additional copper layer only on the flying lead portions. This segmentation of the manufacturing process allows for controlled thickness variation without requiring completely different fabrication approaches, managing complexity through process sequencing.
Solution Approach 2:
The patent uses preliminary action by depositing the additional copper layer on the flying lead portions before finalizing the complete conductor structure. This preliminary reinforcement step is taken during the fabrication process rather than requiring post-manufacturing modifications, integrating the strength enhancement into the standard manufacturing flow.
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 doubly thick flying leads provide sufficient mechanical strength to prevent damage during handling, while the thin stacked conductors maintain desirable impedance characteristics and flexibility for suspension circuits, allowing the gimbal to pitch and roll freely.
Implementation Method 1
a first signal conductor is electrodeposited on a support of stainless steel and a first insulating layer
Implementation Method 2
a second conductor is added with copper plating on both supported and unsupported portions
Data Source
AI summary
A multi-layer circuit such as for a disk drive suspension has two regions: a supported region in which first and second stacked signal conductors are supported on a stainless steel support layer and an insulating layer, and an unsupported region having flying leads in which the flying leads are not supported below by the support layer. The two stacked signal conductors are formed by two separate plating operations, the two plating operations simultaneously creating the flying leads and the unsupported portions of the signal conductors, such that the flying leads have thicknesses that are the sum of the thicknesses of the individual conductors. Crossbars and vias allow the different plating layers to be connected together. This construction allows the individual conductors to be relatively thin and flexible for good electrical and mechanical performance, while creating relatively thick flying leads that are resistant to handling damage.