Flexible Wiring Substrate Protrusion for Input Device Air Bubble Control
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Solution Overview
Problem
In touch panels, the air bubble formed between the sensor unit and the optical layer due to the step created by the flexible substrate's thickness leads to poor appearance and increased manufacturing steps, and existing solutions either require additional resin injection or large buffer regions to mitigate this, which are not feasible for modern design demands.
Innovation Solution
The input device design includes a flexible wiring substrate with a protruding part that absorbs the step of the optical layer, using a conductive joining member that does not extend beyond the protruding part, and a protection layer to minimize the air bubble region, allowing for a narrower buffer zone and improved appearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the flexible substrate connection region is held between the base member and optical layer to obtain sufficient connection strength, then the connection strength is improved, but an air bubble region is created that deforms the optical layer and causes poor appearance
Solution Approach 1:
The flexible substrate is divided into a connection region and a protruding part. The protruding part extends beyond the optical layer's end position, segmenting the flexible substrate's structure to allow the connection region to be held between layers while the protruding part absorbs the step and prevents air bubble formation in the optical layer region.
Solution Approach 2:
The protruding part of the flexible substrate acts as an intermediary element between the connection region and the optical layer. It absorbs the thickness step of the optical layer and prevents direct contact between the air bubble-prone region and the optical layer, thereby eliminating the harmful effect while maintaining connection strength.
2Object-generated harmful factors
If resin is injected into the space between transparent base member and surface member to prevent air bubbles, then air bubble occurrence is prevented, but the number of manufacturing steps increases
Solution Approach 1:
The harmful air bubble formation mechanism is extracted and eliminated by redesigning the flexible substrate structure. Instead of injecting resin to counteract the air bubble problem, the protruding part structure prevents air bubble formation at the source by absorbing the optical layer's thickness step, thereby solving the problem without adding manufacturing steps.
3Reliability
If a large buffer region is provided between the air bubble region and detection region to prevent air bubble impact, then detection region protection is improved, but the width of the peripheral region increases
Solution Approach 1:
The protruding part of the flexible substrate converts the harmful air bubble formation into a beneficial structure. By extending the flexible substrate beyond the optical layer's end, the protruding part absorbs the thickness step and prevents air bubbles from forming in the first place, thereby protecting the detection region without requiring additional buffer space.
Data Source
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AI summary
An input device according to an aspect of the present invention includes a sensor unit, an optical layer superimposed on the sensor unit, and a flexible wiring substrate having a connection region held between the optical layer and the support base member. The flexible wiring substrate has a flexible base member on which an electrode layer is provided and a wiring end that is an end of the electrode layer and is connected to the terminal part so as to be conductive with the terminal part with use of a conductive joining member. The wiring end is located at a position set back from an end of the flexible base member, so that the flexible base member has a protruding part that protrudes toward the sensing region side. Since the input device has, on the sensing region side relative to a front end of the protruding part, a part into which the conductive joining member does not stick out, a region where an air bubble formed between the sensor unit and the optical layer is present can be narrowed.