Ground Spring Strain Relief for High-Frequency Signal Reliability
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Solution Overview
Problem
Existing ground springs in test and measurement equipment fail to maintain reliable connections for high-frequency signals, particularly above 20GHz, and tend to lose their spring function after repeated cycles of connector insertion and removal, leading to data dropouts.
Innovation Solution
A ground spring with a generally annular base and elongated, tapered spring fingers that radiate inwardly, forming a substantially circular opening, made from Beryllium Copper with gold plating, is designed to maintain contact with the ground end of a BMA connector, distributing stress across the spring to prevent deformation and ensure consistent electrical connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ground springs are used, then the structure is simple, but the reliability of high-frequency signal connection deteriorates
Solution Approach 1:
The ground spring is divided into multiple elongated spring fingers (typically 3-5 fingers) that radiate from a central base portion. Each finger acts as an independent contact element, ensuring that if one finger fails or deforms, others can still maintain electrical connection. This segmentation directly improves connection reliability for high-frequency signals while distributing mechanical stress across multiple points.
Solution Approach 2:
The spring fingers are designed with elastic properties to provide dynamic contact pressure. The fingers can flex and deform elastically during connector insertion and removal cycles, maintaining consistent contact force with the ground end of the BMA connector. This dynamic behavior ensures reliable electrical connection despite mechanical wear and thermal expansion/contraction.
2Duration of action of moving object
If conventional ground springs are used, then manufacturing is simple, but the spring function is lost after few cycles
Solution Approach 1:
The ground spring is constructed from beryllium copper, a composite material combining beryllium (2-3%) with copper. This alloy provides exceptional elastic properties, high strength, and excellent electrical conductivity. The material enables the spring fingers to withstand hundreds or thousands of insertion/removal cycles while maintaining their elastic recovery capability, preventing permanent deformation that would cause loss of spring function.
Solution Approach 2:
The spring fingers are designed with specific geometric parameters including tapered cross-sections (wider at base, narrower at tips), optimized lengths, and controlled thicknesses (typically 0.064mm). These parameter optimizations ensure the fingers operate within their elastic limit during normal use, maximizing cycle lifespan. The aslant angle of the longitudinal axis relative to the reference line further optimizes stress distribution.
3Reliability
If conventional ground springs are used, then the structure is straightforward, but signal dropouts occur at high frequencies
Solution Approach 1:
The spring fingers feature non-uniform cross-sections with tapered geometry - wider at the base for structural support and narrower at the tips for optimized contact. The fingers also have aslant angles relative to radial lines, creating local variations in contact pressure distribution. This local quality optimization ensures uniform electrical contact across the ground end surface, preventing signal dropouts at high frequencies by maintaining consistent impedance.
Solution Approach 2:
The ground spring base portion has a generally dished shape with a radius of curvature that provides strain relief. The curved geometry distributes mechanical stress more evenly during connector mating, preventing stress concentration that could lead to finger deformation or contact loss. The circular arrangement of spring fingers also provides symmetrical load distribution.
4Strength
If conventional ground springs are used, then material usage is minimal, but stress concentration causes deformation
Solution Approach 1:
By dividing the ground spring into multiple fingers, the mechanical stress during connector insertion and removal is distributed across several contact points rather than concentrated on a single element. Each finger carries a portion of the total load, reducing stress concentration and preventing deformation. This segmentation allows using less total material while achieving higher strength through distributed load bearing.
Solution Approach 2:
Beryllium copper provides high strength-to-weight ratio and exceptional elastic properties, allowing the spring fingers to be thin (0.064mm) yet resistant to deformation. The material's high yield strength ensures fingers remain within elastic limits under operational stress, while its excellent electrical conductivity maintains signal integrity. This composite material enables minimal material usage without sacrificing stress resistance.
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 ground spring effectively maintains a solid electrical connection for high-frequency signals, reducing signal dropouts and extending the lifespan of the spring by keeping the fingers within their elastic limit, allowing for hundreds or thousands of cycles without losing functionality.
Implementation Method 1
The ground spring is preferably formed from Beryllium Copper having gold plating thereon
Implementation Method 2
Each of the elongate spring fingers has a longitudinal axis that is aslant from a reference line extending from the center of the ground spring to a center of the base portion by approximately 40 degrees
Data Source
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AI summary
A ground spring for receiving a ground end of a high-frequency test probe is described. The ground spring includes a generally annular base portion, and a number of elongated spring fingers extending from the base portion. The fingers extend generally radially inwardly from the base portion and have inner end faces that together define a substantially circular opening in a center portion of the ground spring. Each of the fingers have a tapered shape including a wider base portion end and a narrower inner end portion Each of the fingers has a longitudinal axis that is aslant relative to a reference line extending from the center of the ground spring to a center of the base portion of each finger. BMA connectors including the ground spring and test and measurement devices are also described.