Composite Press Fit Bushing for PCB Mounting Stress Reduction
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Solution Overview
Problem
Existing methods for mounting printed circuit boards (PCBs) to structures using metal screws can cause stress and bowing due to the rigidity of metal bushings, and existing plastic solutions do not provide sufficient mechanical retention and electrical isolation.
Innovation Solution
A two-piece press fit mounting bushing comprising a metal inner cylindrical piece with a knurled surface and a plastic outer piece that forms a tight interference fit with the PCB, providing mechanical retention and electrical isolation while minimizing stress on the PCB.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metal screws and metal bushings are used for mounting PCB, then mechanical strength and retention are improved, but stress and bowing of PCB increase due to rigidity
Solution Approach 1:
The mounting bushing combines a metal inner piece (providing strength and retention) with a plastic outer piece (providing electrical isolation and stress reduction). This composite structure resolves the contradiction by allowing the metal component to provide mechanical retention while the plastic component reduces stress transmission to the PCB and provides electrical isolation.
Solution Approach 2:
Different parts of the bushing have different material properties optimized for specific functions: the inner metal piece provides structural strength and thread engagement, while the outer plastic piece provides electrical isolation and stress distribution. This local differentiation of material properties allows simultaneous achievement of strength and stress reduction.
2Reliability
If plastic bushings are used for mounting PCB, then electrical isolation is improved, but mechanical retention and security are insufficient
Solution Approach 1:
The dual-material construction places the plastic outer piece in direct contact with the PCB for electrical isolation, while the metal inner piece provides the structural strength for thread engagement and retention. This composite approach simultaneously achieves both electrical isolation and mechanical retention.
Solution Approach 2:
The metal inner piece is nested within the plastic outer piece, with the metal component providing internal structural support and thread formation, while the plastic component provides external electrical isolation. This nested arrangement allows both materials to perform their specialized functions simultaneously.
3Strength
If tight interference fit is formed with PCB, then mechanical retention is improved, but stress on PCB increases
Solution Approach 1:
The plastic outer piece changes the mechanical parameters of the bushing-PCB interface by providing a softer, more compliant material that can form a tight interference fit while distributing stresses over a larger area and reducing peak stress concentrations on the PCB.
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 secure and stress-reducing mounting of PCBs by forming a tight interference fit with the PCB, preventing bowing and ensuring reliable electrical isolation, while allowing for secure attachment to a mounting structure.
Implementation Method 1
an outer piece (36) made from a plastic material that is molded to and in contact with the knurled portion (30) so as to be adhered and fixed to the inner piece (26)
Implementation Method 2
A portion (30) of the outer wall (32) of the inner piece (26) has a knurled surface or, at least, a surface that has a rough texture
Implementation Method 3
The outer piece being plastic electrically isolates the inner piece from the printed circuit board (22)
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A circuit board mounting arrangement is provided including a circuit board and a press fit mounting bushing including a cylindrical inner piece and an outer piece secured to the inner piece. The outer piece has a plurality of radially projecting, deformable elements and the circuit board has a cylindrical opening having a diameter less than an outer diameter of the radially projecting deformable elements. The deformable elements deform when the mounting bushing is pushed into the cylindrical opening of the circuit board so as to hold the mounting bushing to the circuit board. The circuit board and press fit bushing are then overmolded.