Stretchable Mounting Board Bismuth Electrode Layers
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Solution Overview
Problem
Conventional stretchable mounting boards experience disconnection of wiring due to the formation of brittle metal compounds when expanding or contracting, and have insufficient electrical and mechanical connections between solder and conductors.
Innovation Solution
A stretchable mounting board with a substrate, stretchable wiring, a mounting electrode section, and solder that includes bismuth and tin, where the mounting electrode section has a first electrode layer with lower bismuth concentration facing the wiring and a second electrode layer with higher bismuth concentration facing the solder, preventing the formation of brittle compounds and ensuring a stable connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder is used to connect the stretchable wiring to the mounting board, then electrical connection is achieved, but brittle metal compounds form causing wiring disconnection during expansion and contraction
Solution Approach 1:
A mounting electrode section is introduced as an intermediary between the stretchable wiring and the solder. This electrode section includes a first electrode layer (e.g., Cu-Ni alloy) that contacts the stretchable wiring and a second electrode layer (e.g., Sn-Ag alloy) that contacts the solder, preventing direct contact between the stretchable wiring and solder, thereby suppressing the formation of brittle metal compounds at the wiring-solder interface.
Solution Approach 2:
The mounting electrode section uses composite material structures with specific alloy compositions. The first electrode layer uses Cu-Ni alloy (e.g., Cu-10wt% Ni) to provide good adhesion to stretchable wiring, while the second electrode layer uses Sn-Ag alloy (e.g., Sn-3wt% Ag) to ensure good solderability, creating a composite structure that balances adhesion and solderability requirements.
2Ease of manufacture
If conventional electrode materials are used, then manufacturing is simplified, but wettability of solder with respect to the conductor is insufficient
Solution Approach 1:
The invention changes the material parameters of the electrode layers to optimize solder wettability. The second electrode layer is designed with Sn-Ag alloy composition (e.g., Sn-3wt% Ag) which has superior wettability characteristics compared to conventional materials, ensuring reliable solder joints while maintaining manufacturability through established alloy systems.
Data Source
AI summary
A stretchable mounting board that includes a stretchable substrate having a main surface, a stretchable wiring disposed on the main surface of the stretchable substrate, a mounting electrode section electrically connected to the stretchable wiring, solder electrically connected to the mounting electrode section and including bismuth and tin, and an electronic component electrically connected to the mounting electrode section with the solder interposed therebetween. The mounting electrode section has a first electrode layer on a side thereof facing the stretchable wiring and which includes bismuth and tin, and a second electrode layer on a side thereof facing the solder and which includes bismuth and tin. A concentration of the bismuth in the first electrode layer is lower than a concentration of the bismuth in the second electrode layer.