Press-Fit Terminal Spring Geometry for Balanced Insertion and Holding
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Solution Overview
Problem
Existing press-fit terminals with a plate thickness of 0.75 to 0.85 mm face a challenge in balancing insertion force, holding force, and contact area, with excessive insertion force potentially damaging the board and insufficient holding force and contact area affecting electrical connection reliability.
Innovation Solution
A press-fit terminal design with specific geometric parameters, including cross-sectional secondary moments and gradient conditions for spring portions, balances insertion force, holding force, and contact area by optimizing the shape and deformation characteristics of the terminal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the plate thickness of the press-fit terminal is increased to 0.75-0.85 mm for structural strength, then the holding force and contact area are improved, but the insertion force becomes excessively large causing board damage
Solution Approach 1:
The press-fit terminal is divided into multiple functional segments: a tip portion with reduced thickness for low insertion force, a press-fit portion with optimized spring portions for controlled deformation and holding force, and a base portion for electrical connection. This segmentation allows each part to perform its specific function optimally without compromising the whole
Solution Approach 2:
The patent optimizes specific geometric parameters including the cross-sectional secondary moment of area (I) of spring portions, the gradient (θ) of front spring portions, and the thickness distribution along the terminal length. By precisely controlling parameters like I tan θ within specific ranges, the terminal achieves balanced insertion and holding forces
2Reliability
If the plate thickness is increased to 0.75-0.85 mm to improve contact area and holding force, then electrical connection reliability is improved, but the insertion force becomes too large and may damage the board
Solution Approach 1:
The terminal structure is segmented into a tip portion (smaller thickness) for insertion, a press-fit portion (optimized thickness 0.75-0.85 mm) for reliable electrical connection, and a base portion. This allows the contact-critical section to have sufficient thickness for reliability while the insertion section maintains low force
Solution Approach 2:
Different sections of the terminal have different thickness qualities tailored to their functions: the tip portion has reduced thickness for easy insertion, while the press-fit portion has optimized thickness (0.75-0.85 mm) for reliable electrical contact and holding force
3Force
If the insertion force is reduced for easier insertion and board protection, then board damage is suppressed, but the holding force and contact area may become insufficient
Solution Approach 1:
The terminal is segmented into a tip portion for low-force insertion and a press-fit portion with optimized spring portions for high holding force. The spring portions are specifically designed with cross-sectional secondary moments and gradients that enable them to deform during insertion and then provide strong holding force
Solution Approach 2:
The spring portions are designed to dynamically deform during the insertion process, absorbing insertion force through elastic deformation, and then maintain the terminal in a firmly held state through their spring-back force, providing both easy insertion and strong holding
Data Source
AI summary
A press-fit terminal is provided with a press-fit portion including two contact pieces facing each other across an eye hole. Each of the two contact pieces includes a parallel portion in parallel to that of the other contact piece, a front spring portion and a rear spring portion. A thickness of the press-fit portion is 0.75 mm or more and 0.85 mm or less. When G1 [mm3] and G2 [mm3] denote cross-sectional secondary moment of area per unit length of the front spring portion and cross-sectional secondary moment of area per unit length of the rear spring portion for the press-fit portion, G1+G2 is 0.030 or more and 0.080 or less. Further, when θ denotes a gradient of the front spring portion with respect to an inserting direction of the press-fit portion, G1 tan θ is 0.0024 or more and 0.0070 or less.