Curable Composition for Flexible Wiring Boards
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Solution Overview
Problem
Existing curable compositions for flexible wiring boards face challenges in achieving optimal flexibility, low warpage, and long-term electrical insulation reliability, particularly with reduced wiring pitches, leading to issues like wiring breakage during assembly.
Innovation Solution
A curable composition comprising a carboxyl group-containing polyurethane with an aromatic ring concentration of 0.1 to 4.5 mmol/g, combined with a solvent and a compound having two or more epoxy groups, which is screen-printed and cured to form an overcoat film that inhibits wiring breakage and ensures excellent adhesion and insulation properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If existing curable compositions are used to achieve flexibility, then flexibility is improved, but warpage increases and electrical insulation reliability deteriorates
Solution Approach 1:
The patent uses a composite resin composition containing both a polyol (providing flexibility) and an isocyanate compound (providing structural integrity and electrical insulation). This composite system allows the cured product to simultaneously achieve flexibility and long-term electrical insulation reliability, resolving the contradiction between ease of operation and reliability.
2Ease of operation
If resin composition is modified to improve flexibility, then flexibility is improved, but heat resistance and chemical resistance deteriorate
Solution Approach 1:
The patent carefully selects and balances the molecular weight, hydroxyl value, and structural parameters of the polyol and isocyanate compounds. By optimizing these parameters, the cured product achieves flexibility while maintaining heat resistance and chemical resistance, resolving the contradiction between ease of operation and temperature resistance.
3Productivity
If wiring pitch is reduced for miniaturization, then productivity is improved, but wiring breakage increases
Solution Approach 1:
The patent employs a flexible overcoat film formed from the cured resin composition that conforms to and protects the flexible substrate with reduced wiring pitches. The film's flexibility allows it to accommodate the strained wiring patterns without causing breakage, enabling miniaturization while maintaining wiring integrity.
4Ease of operation
If carboxyl group-containing polyurethane and epoxidized polybutadiene are used, then flexibility is improved, but phase separation occurs during drying
Solution Approach 1:
The patent changes the chemical parameters by using a polyol with controlled molecular weight and hydroxyl value, combined with a specific isocyanate compound. This parameter optimization prevents phase separation during the drying process while maintaining flexibility in the cured product, resolving the contradiction between ease of operation and composition stability.
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 provides a flexible wiring board with reduced warpage, improved flexibility, and enhanced long-term electrical insulation reliability, preventing wiring breakage and facilitating IC chip mounting.
Implementation Method 1
a cured film formed by curing the curable composition
Implementation Method 2
when the composition is dried for solvent removal
Data Source
AI summary
A curable composition for forming an overcoat film for flexible wiring boards, the curable composition being effective in improving adhesion to substrates, low warpage, flexibility, the property of inhibiting wire breakage, and long-term reliability. The curable composition according to the present invention comprises a polyurethane (component a) having carboxyl groups and an aromatic-ring concentration of 0.1-6.5 mmol/g and containing an organic residue derived from a polyisocyanate, a solvent (component b), and a compound (component c) having two or more epoxy groups in the molecule.