Flexible Substrate-Bus Bar Connection Using a Nickel Intermediary
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Solution Overview
Problem
The joining strength between flexible printed wiring boards and bus bars is reduced due to the formation of intermetallic compounds, especially when copper and aluminum are used, leading to brittleness and misalignment issues with relay members.
Innovation Solution
A connection structure involving a flexible substrate with conductive paths covered by a resin base material, a bus bar made of a different metal, and a connection piece with a higher joining strength, allowing for brazing and soldering without alignment, using nickel for improved bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper and aluminum are joined through welding, then electrical connectivity is achieved, but intermetallic compounds are produced making the joined portion brittle and reducing joining strength
Solution Approach 1:
A nickel relay member is introduced as an intermediary between the copper connection portion on the flexible printed wiring board and the aluminum bus bar. The nickel relay member has high joining strength to both copper and aluminum, preventing the formation of brittle intermetallic compounds while maintaining electrical connectivity. This mediator approach resolves the contradiction by eliminating direct copper-aluminum contact.
2Strength
If a relay member is used to improve joining strength, then joining strength is improved, but misalignment occurs when the flexible printed wiring board and bus bar have different thicknesses
Solution Approach 1:
The nickel relay member is designed with a specific thickness that compensates for thickness differences between the flexible printed wiring board and bus bar. This dynamic design allows the relay member to bridge the gap created by varying thicknesses, maintaining proper alignment during welding without requiring precise pre-alignment of the components.
3Strength
If welding is used to join copper and aluminum, then joining strength is improved, but intermetallic compound formation reduces reliability
Solution Approach 1:
The nickel relay member serves as a mediator that prevents direct welding between copper and aluminum, thereby preventing the formation of brittle intermetallic compounds. The nickel layer maintains both mechanical strength and electrical conductivity while ensuring reliable long-term performance by eliminating the harmful chemical reaction between dissimilar metals.
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
Enhances the joining strength and reduces manufacturing costs by preventing misalignment and oxide film formation, while maintaining electrical connectivity.
Implementation Method 1
the bus bar is joined to the connection piece through welding
Implementation Method 2
the connection land is joined to the connection piece through brazing and soldering
Implementation Method 3
the connection land is joined to the connection piece through brazing and soldering
Data Source
AI summary
A connection structure between a flexible substrate and a bus bar includes: a flexible substrate; a plurality of bus bars; and a connection piece, in which the flexible substrate is formed by being covered by a plurality of conductive paths containing a first metal, and a resin base material, the bus bars are formed so as to contain a second metal, the conductive paths include a second conductive path extending from a first conductive path, the resin base material includes a sub-film portion that is branched from a main film portion and extends over the bus bars, the second conductive path is disposed on the sub-film portion, the connection piece is formed so as to contain a third metal that has a higher joining strength of welding to the first metal and the second metal than a joining strength of welding between the first metal and the second metal.