Wiring Substrate with Exposed Optical Waveguide Core for High Efficiency Coupling
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Solution Overview
Problem
Existing optical component mounting substrates face challenges in achieving high optical coupling efficiency and reliable electrical connections due to the interference of clad layers between optical waveguides and components, leading to suboptimal performance in both optical and electrical connectivity.
Innovation Solution
A wiring substrate design featuring an insulating layer with a conductor pad, a covering layer, an optical waveguide with a core part that has an exposed side surface facing the opposite direction, and conductor posts made of plating metal that penetrate the covering layer, allowing for direct optical coupling with components and improved electrical connectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a covering layer is formed over the insulating layer to protect the conductor pad, then the reliability of electrical connections is improved, but the optical coupling efficiency between the optical waveguide and component deteriorates due to interference with light transmission
Solution Approach 1:
The insulating layer is divided into two functional regions: a first region without the covering layer that allows optical coupling, and a second region with the covering layer that provides electrical protection. This segmentation enables simultaneous achievement of optical efficiency and electrical reliability.
Solution Approach 2:
The covering layer is applied locally only to specific regions where electrical protection is needed, while leaving other regions uncovered to maintain optical transmission properties. This local differentiation of structure allows each region to optimize its specific function.
2Loss of energy
If the core part of the optical waveguide is positioned closer to the conductor pad for better optical coupling, then the optical coupling efficiency is improved, but the electrical insulation between the conductor pad and component deteriorates
Solution Approach 1:
The insulating layer is segmented into a first region (without covering layer) for optical coupling and a second region (with covering layer) for electrical insulation. This allows the core part to be positioned close to the conductor pad for optimal optical coupling while the covering layer in the second region maintains electrical insulation.
Solution Approach 2:
The insulating layer acts as an intermediary structure with differentiated regions: the first region enables optical interaction while the second region with the covering layer provides electrical isolation. This intermediary structure resolves the conflict between optical proximity and electrical insulation.
3Reliability
If the covering layer is made thicker to improve electrical protection, then the reliability of electrical connections is improved, but the distance for optical coupling increases causing signal loss
Solution Approach 1:
The covering layer is segmented to exist only in the second region of the insulating layer, while the first region remains uncovered. This allows the covering layer to be thick enough for electrical protection where needed, while maintaining short optical coupling paths where light transmission is required.
Solution Approach 2:
The covering layer thickness is optimized locally: thick in the second region for electrical protection, and absent in the first region for optimal optical coupling. This local quality differentiation eliminates the trade-off between protection thickness and coupling distance.
Data Source
AI summary
A wiring substrate includes an insulating layer, a conductor layer formed on surface of the insulating layer and including a conductor pad, a covering layer covering a portion of the insulating layer, an optical waveguide positioned on the surface of the insulating layer and including core part, and a conductor post including plating metal and formed on the conductor pad such that the post is penetrating through the covering layer and connected to a component. The insulating layer has component region covered by the component when the component is connected, the core part has side surface extending in direction along the surface of the insulating layer, the side surface has an exposed portion exposed in the component region and facing the opposite direction with respect to the insulating layer, and distance between the exposed portion and the surface of the insulating layer is greater than thickness of the covering layer.