Flat Resin Block for Electrical Junction Box Solder Crack Prevention
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Solution Overview
Problem
Conventional electrical junction boxes experience solder cracks due to relative displacement between the printed circuit board and resin blocks with different linear expansion coefficients, and the cost of manufacturing leg-equipped resin blocks is high due to the need for custom molds for each shape.
Innovation Solution
A flat-shaped resin block formed from the same printed circuit board material is used, supported by separate block-receiving portions, eliminating the need for custom molds and reducing the risk of solder cracks by matching the linear expansion coefficient of the printed circuit board.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a leg-equipped resin block made of synthetic resin is used to hold the board terminal, then the board terminal can be securely held and supported, but solder cracks occur due to relative displacement caused by difference in linear expansion coefficients between the resin block and printed circuit board
Solution Approach 1:
The patent changes the material parameter (linear expansion coefficient) of the resin block to match that of the printed circuit board, thereby eliminating relative displacement during thermal expansion and contraction cycles, preventing solder cracks while maintaining holding strength
Solution Approach 2:
The patent makes the resin block and printed circuit board homogeneous in terms of material composition and thermal expansion characteristics, ensuring they expand and contract together without causing stress concentration at the solder joints
2Manufacturing precision
If custom leg-equipped resin blocks are manufactured for each electric component or connector shape, then the resin block can be precisely fitted to each component, but manufacturing costs increase due to the need for expensive custom molds
Solution Approach 1:
The patent creates a universal resin block design that can accommodate multiple different electric components and connectors through a standardized structure with adjustable or adaptable features, eliminating the need for separate custom molds for each component type while maintaining precise fit through design flexibility
Solution Approach 2:
The patent divides the resin block into functional segments or modular components that can be configured or adjusted to fit different electric components, allowing a single mold to produce versatile blocks that can be adapted to various shapes and sizes through assembly or configuration rather than requiring separate molds for each component type
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
This configuration reduces solder crack occurrence and lowers manufacturing costs by using a simple, cost-effective approach to support the resin block and maintain alignment during soldering, while ensuring stable support and easy assembly.
Implementation Method 1
since this kind of leg-equipped resin block is formed of a synthetic resin material such as polypropylene whose linear expansion coefficient differs greatly from that of the base material of the printed circuit board, there is a problem in that when holding a board terminal using this kind of leg-equipped resin block, solder cracks tend to occur due to relative displacement between the board terminal and the printed circuit board based on the difference in linear expansion coefficients
Data Source
AI summary
Provided is an electrical junction box with a novel structure with which the occurrence of solder cracks can be advantageously avoided, while also achieving a reduction in manufacturing costs. In an electrical junction box including an terminal-equipped printed circuit board in which an intermediate section of a board terminal in the length direction is press-fitted into and held by a resin block, and a lead portion of the board terminal is connected to a conductive path of a printed circuit board by soldering, the resin block is formed of a flat-shaped printed circuit board base material, and is arranged on the printed circuit board with a gap therebetween, and the resin block is supported in a fixed position on the printed circuit board by a block-receiving portion that is separate from the resin block.