Polyurethane Film for Bendable Circuit Boards
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Solution Overview
Problem
Current bendable wiring boards made from rigid materials like polyethylene terephthalate (PET) and polyimide (PI) lack adhesion and are prone to peeling due to stress, and existing stretchable electronics have low heat resistance, preventing sufficient conductivity and flexibility for wearable devices and biosensors.
Innovation Solution
A polyurethane film synthesized by reacting a long-chain polyol with a polyisocyanate, providing a storage elastic modulus of 20 to 200 MPa at 25°C, tensile strength of 20 to 80 MPa, and elongation at break of 500 to 900%, allowing for excellent contact feeling and resistance to bending, combined with circuit wiring for enhanced adhesion and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If rigid plastic materials like PET, PI, PEEK, PPS, PAR, PC, TAC, or CAP are used for flexible printed wiring, then structural strength and dimensional stability are improved, but the wiring board cannot return to its original shape after bending, has low adhesion between metal wiring and board, and metal wiring may peel off or break due to stress
Solution Approach 1:
The patent changes the fundamental material parameter from rigid plastics to elastomers, transforming the mechanical properties from brittle to flexible. This allows the substrate to elastically deform and return to its original shape, preventing wiring breakage and peeling while maintaining structural integrity through the elastomer's inherent elasticity and recovery capability
Solution Approach 2:
The patent employs composite material structures where elastomer substrates are combined with metal wiring patterns. The elastomer provides flexibility and adhesion, while the metal wiring provides electrical conductivity. This composite approach resolves the contradiction by allowing the substrate to deform elastically without compromising the wiring's structural strength or adhesion
2Adaptability or versatility
If elastomeric materials are used for stretchable electronics, then flexibility and elasticity are improved, but heat resistance deteriorates, preventing heating at temperatures around 120°C which is required for sufficient sintering of conductive fine particles
Solution Approach 1:
The patent modifies the thermal parameter of elastomeric materials by selecting or developing elastomers with enhanced heat resistance that can withstand temperatures around 120°C. This allows the material to maintain its flexibility and elasticity while achieving sufficient thermal stability for sintering conductive particles, thus resolving the contradiction between flexibility and heat resistance
3Manufacturing precision
If conventional lithography technology is used for producing ICs, then manufacturing precision and performance are improved, but cost increases significantly compared to printing technologies
Solution Approach 1:
The patent replaces the complex mechanical lithography system with a simpler printing technology system. Instead of using expensive vacuum processes and sophisticated lithography equipment, the invention employs printing methods to deposit conductive materials directly onto elastomer substrates, significantly reducing manufacturing cost while maintaining acceptable circuit wiring precision through the printing process's inherent capability to form fine patterns
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 polyurethane-based bendable wiring board offers excellent contact feeling, high flexibility, and resistance to bending and folding, maintaining conductivity and adhesion, suitable for wearable devices and biosensors with improved heat resistance and durability.
Implementation Method 1
a film composed of a polyurethane synthesized by allowing a long-chain polyol to react with a polyisocyanate
Data Source
AI summary
Provided are an expandable or bendable circuit board having good body-contact feel, strong against bending and folding, and an electronic device made therefrom. The bendable circuit board includes: a film comprising a polyurethane synthesized by reacting a long-chain polyol with polyisocyanate and having a storage modulus at 25° C. of 20 to 200 MPa, a tensile strength of 20 to 80 MPa, and an elongation at break of 500 to 900%, and the temperature of which the storage elastic modulus reaches to 1 MPa is at 155° C. or higher; and circuit wiring formed in contact with a surface of the film. Alternatively, an expandable circuit board having the ratio ρ/ρ0 of the specific electrical resistance ρ of the circuit wiring when the circuit wiring is expanded to the specific electrical resistance (Ω·cm) ρ0 of the circuit wiring before the circuit wiring is expanded is within a range of 1.05 to 10.0.