Shielded Flex Cable Apertures for Disk Drive RFI Noise
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Solution Overview
Problem
Prior art flexible signal cables in disk drives suffer from electromagnetic interference due to ungrounded aluminum stiffeners, which couple radio-frequency interference (RFI) to signal traces, leading to noise and potential failure during testing, and existing solutions like grounding the stiffener result in increased RFI or require costly design changes.
Innovation Solution
A shielding layer is added directly to the flexible signal cable at the bracket end and under the first stiffener, made of copper with a thickness greater than the skin depth at expected RFI frequencies, and featuring a pattern of apertures to maintain impedance, grounded separately from the signal ground to direct RFI noise away from sensitive traces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a continuous shielding layer is added under signal traces, then electromagnetic interference protection is improved, but impedance control deteriorates
Solution Approach 1:
The shielding layer is segmented by introducing apertures that divide the continuous conductive layer into isolated regions. This segmentation allows the shielding to protect against electromagnetic interference while preventing the formation of continuous capacitive coupling that would disrupt signal impedance. The apertures create discrete shielding zones rather than a uniform barrier.
Solution Approach 2:
The shielding layer is positioned locally under specific signal traces where electromagnetic interference is most problematic, rather than providing uniform coverage across the entire flex cable. The apertures are strategically placed to maintain shielding effectiveness in critical areas while preserving impedance control in signal-carrying regions.
2Object-affected harmful factors
If the shielding layer is connected to signal ground, then RFI noise reduction is improved, but RFI excitation increases
Solution Approach 1:
The shielding layer is extracted from the signal ground connection and instead connected to a dedicated RFI ground. This separation removes the shielding layer's interaction with signal traces, preventing it from acting as an antenna that would excite RFI in the signal paths while still providing noise reduction through proper grounding to the RFI ground network.
Solution Approach 2:
A dedicated RFI ground serves as an intermediary between the shielding layer and the signal ground. This intermediate connection allows the shielding layer to dissipate RFI noise without creating direct coupling paths that would excite resonances in the signal traces. The RFI ground acts as a buffer that isolates the shielding's electromagnetic interactions from the sensitive signal paths.
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 shielding layer effectively reduces RFI excitation of resonances in the flex region, preventing noise contamination of signal traces while maintaining optimal impedance, thereby enhancing signal integrity and reliability during RFI testing.
Implementation Method 1
A shielding layer is added directly to the flexible signal cable at the bracket end and under the first stiffener, made of copper with a thickness greater than the skin depth at expected RFI frequencies
Implementation Method 2
made of copper with a thickness greater than the skin depth at expected RFI frequencies
Implementation Method 3
featuring a pattern of apertures to maintain impedance
Data Source
AI summary
A flex cable with a shielding layer for use in a disk drive is described. The flex cable connects the actuator to the system electronics. The flex cable has a shielding layer that provides RF shielding for the embedded signal traces. In embodiments the shielding layer is connected to the baseplate or device enclosure ground at one or more selected points on the bracket end of the flex cable that are separated from the signal paths. Embodiments of the shielding layer include rows of apertures or windows that are aligned with selected signal traces such as the read and write signal traces and serve to maintain the desired impedance in the read and write signal traces. In one embodiment the shielding layer extends over a selected portion of the flex cable that includes the bracket end and the area under the first stiffener.