Windowed Stainless Steel Suspension Circuit Traces for Low Impedance
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Solution Overview
Problem
Current suspension technologies for disk drives, such as CIS and TSA flexures, face limitations in achieving impedance below 30 ohms and bandwidth above 6 GHz, which are required for future hard disk drive designs, due to restricted spacing between traces and ground layers.
Innovation Solution
A suspension design featuring circuit traces on both sides of a stainless steel layer with strategically placed windows allows electric fields to pass through, enabling increased coupling and resulting in high bandwidth and low impedance, particularly beneficial for differential signal routing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional CIS or TSA flexure technologies are used with limited spacing between traces and ground layer, then manufacturing is simpler, but impedance cannot be reduced below 30 ohms and bandwidth cannot exceed 6 GHz
Solution Approach 1:
The patent transitions from a single-layer trace structure to a multi-layer stacked trace configuration. By adding vertical dimensionality with multiple circuit layers separated by dielectric layers, the design achieves lower impedance (below 30 ohms) and higher bandwidth (above 6 GHz) while maintaining manufacturability through standardized layering processes.
Solution Approach 2:
The patent employs composite material structures combining multiple conductive layers (copper or copper alloy traces), dielectric layers (polyimide or similar materials), and stainless steel support layers. This composite approach enables precise impedance control and enhanced bandwidth by optimizing the electromagnetic characteristics of each material layer.
2Manufacturing precision
If stacked traces are used to achieve impedance below 50 ohms, then impedance requirement is met, but bandwidth is limited to less than 3 GHz
Solution Approach 1:
The patent segments the ground reference into multiple separate ground traces positioned adjacent to each signal trace in the stacked configuration. This segmentation creates multiple return paths for the electromagnetic signal, reducing signal integrity degradation and enabling bandwidth exceeding 6 GHz while maintaining impedance below 30 ohms through optimized trace spacing and ground trace arrangement.
3Manufacturing precision
If interleaved traces are used to achieve impedance below 50 ohms, then impedance requirement is met, but bandwidth is limited to less than 7 GHz
Solution Approach 1:
The patent utilizes vertical stacking of circuit layers separated by dielectric layers to achieve impedance control, rather than relying solely on lateral interleaving. This vertical dimensionality, combined with adjacent ground traces providing multiple return paths, enables bandwidth above 6 GHz while maintaining impedance below 30 ohms, surpassing the limitations of traditional interleaved trace designs.
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 achieves a bandwidth of over 7 GHz and impedance below 30 ohms, surpassing the limitations of existing technologies, making it suitable for advanced disk drive requirements.
Implementation Method 1
The stainless steel layer is constructed with one or more windows, e.g., holes, such that traces of the circuit layers pass over the window(s). Consequently, when the traces carry a signal, an electric field generated by the signal will pass between the traces via the window(s).
Data Source
AI summary
An electrical circuit for a disk drive suspension has a first signal trace above a grounded support layer which is typically stainless steel, and a second signal trace below the support layer, the two signal traces typically being opposite polarities of a differential signal pair. The support layer between the two signal traces is windowed, and the two traces are physically separated by a distance that equals the nominal thickness of the support layer plus the thicknesses of the top and bottom dielectric layers that separate the signal traces from the support layer. The physical separation combined with the windowing reduces the impedance and increases the bandwidth of the differential pair. The impedance can be controlled by the percentage of windowing in the support layer.