Flexible Wiring Board Edge Insulation Design
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Solution Overview
Problem
The challenge is to prevent connection failure in flexible wiring boards due to the interference of a thick insulating layer at the edge portion of the substrate, which is exacerbated by the hardening shrinkage of conductive adhesive bumps, leading to deformation and potential breakage of the bumps.
Innovation Solution
A wiring board design with a flexible substrate featuring first and second connection electrode portions connected via conductive adhesive bumps, where the second wire has a large width portion with a conductive-material absent portion between the edge and the connecting electrode, allowing the insulating layer to be controlled and preventing excessive thickness, thereby reducing deformation stress on the bumps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the insulating layer is formed by applying insulating material to cover the connection surface, then the wiring board achieves proper insulation, but the insulating layer thickness increases in the edge portion causing interference with the actuator during bump hardening shrinkage
Solution Approach 1:
The patent applies local quality by creating a through-hole in the second wire at the edge portion of the flexible substrate, where the hole is filled with insulating material to form a localized insulating structure. This localized approach allows the insulating layer to be present only where needed for insulation, while avoiding excessive thickness in the edge portion that would interfere with actuator operation during bump hardening shrinkage.
2Reliability
If the bump is made of conductive adhesive and hardened by heat, then electrical connection is achieved, but the bump shrinks causing deformation of the substrate toward the actuator
Solution Approach 1:
The patent applies beforehand cushioning by providing a through-hole filled with insulating material in the second wire at the edge portion, before the bump hardening process occurs. This pre-prepared structure acts as a cushion or buffer that allows the substrate to deform during bump hardening shrinkage without the insulating layer interfering with the actuator, thereby accommodating the shape change while maintaining connection reliability.
3Reliability
If the second wire has a large width portion for common electrode connection, then electrical continuity is improved, but the wire occupies more space in the edge portion exacerbating the thickness problem
Solution Approach 1:
The patent applies the porous materials principle by creating a through-hole in the second wire at the edge portion. This hole reduces the effective cross-sectional area of the wire in the edge portion, allowing the large width portion to maintain electrical continuity for the common electrode connection while occupying less space that would otherwise contribute to excessive insulating layer thickness.
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 design effectively restrains the increase in insulating layer thickness at the edge portion, allowing for greater deformation and reducing the risk of connection failure by minimizing the force exerted on the conductive adhesive bumps during hardening shrinkage.
Implementation Method 1
the bump made of the conductive adhesive is caused to shrink when being hardened by heat
Implementation Method 2
the flexible substrate is coated at its terminal surface with an insulating layer
Data Source
AI summary
A wiring board includes: a substrate; first connection electrode portions which are disposed on a surface of the substrate and which are to be connected to individual-electrode connection terminals of an actuator via first bumps; first wires having electrical continuity with the first connection electrode portions; a second connecting electrode portion which is disposed on the surface of the substrate and which is to be connected to the a common-electrode connection terminal of the actuator via a second bump; and a second wire having electrical continuity with the second connection electrode portion. The second connecting electrode portion is located in an edge portion of the substrate. The second wire has a conducive-material absent portion that is located between an edge of the substrate and the second connecting electrode portion.