Optical Packaging Structure With Microlenses for Alignment-Tolerant Coupling
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Solution Overview
Problem
Current semiconductor encapsulation methods face challenges in balancing the need for coupling space and physical protection, particularly in 3D stacked interconnections, where passive alignment in surface coupling processes are inefficient and require stringent placement precision for optical fiber structures.
Innovation Solution
The implementation of microlenses on dummy regions of semiconductor chips to focus light input into optical coupling regions, combined with transparent materials and metal connection pillars, reduces precision requirements and enhances the efficiency of optical coupling processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If surface coupling is used to connect optical fiber structures to PIC chips, then coupling space is reserved and light transmission is enabled, but the coupling process becomes complex and placement precision requirements increase to ±2.5 μm
Solution Approach 1:
The patent applies preliminary action by pre-forming microlenses on the PIC chip surface during the wafer fabrication process, before the optical coupling stage. This pre-positioned optical focusing structure eliminates the need for high-precision placement during subsequent assembly, as the microlenses automatically focus light onto the optical coupling interface regardless of minor positioning variations.
Solution Approach 2:
The patent introduces microlenses as an intermediary optical element between the optical fiber structure and the optical coupling interface. These microlenses serve as mediators that focus and guide light, reducing the stringent alignment requirements between the optical fiber and the chip, thereby lowering the placement precision requirement from ±2.5 μm to ±5 μm.
2Strength
If 3D stacked interconnections are implemented with molding layer encapsulation, then physical protection is provided to chips, but coupling space and light transmission are obstructed
Solution Approach 1:
The patent applies local quality by making the molding layer optically transparent in the region corresponding to the optical coupling interface. This allows the molding layer to provide physical protection to the chips while simultaneously permitting light transmission through the encapsulation structure, thus resolving the conflict between protection and optical access.
Solution Approach 2:
The patent transitions from surface-level optical coupling to three-dimensional optical coupling by forming microlenses that extend vertically from the chip surface. This dimensional change allows light to be focused through the molding layer from above, enabling optical coupling even when the chip surface is encapsulated, thus providing both protection and optical functionality.
3Ease of operation
If passive alignment is used in surface coupling process, then alignment simplicity is achieved, but coupling efficiency decreases and placement accuracy requirements increase
Solution Approach 1:
The patent replaces the mechanical alignment system with an optical self-alignment system. Instead of relying on precise mechanical positioning of optical fibers relative to chip features, the microlenses provide optical self-alignment by focusing light onto the optical coupling interface, thereby maintaining coupling efficiency while simplifying the alignment process and reducing placement accuracy requirements.
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 approach lowers the need for precise alignment, improves coupling efficiency, and increases tolerance for placement errors, while maintaining structural stability and minimizing light loss.
Implementation Method 1
forming a first microlens on the dummy region of the second semiconductor chip corresponding to the optical coupling region to correct light input into the optical coupling region for optical coupling
Implementation Method 2
a curvature of the first microlens and a distance between the first microlens and the optical coupling interface are adjusted to focus light incident on the first microlens onto the optical coupling interface
Implementation Method 3
a material of the second semiconductor chip covering the optical coupling region is transparent to light of a predetermined wavelength
Data Source
Figure 1
Figure 2A~2C
Figure 2D~2F
AI summary
An encapsulation structure and manufacturing method thereof are disclosed. The method includes providing a semiconductor wafer including a plurality of first semiconductor chips. For each first semiconductor chip, a microlens is formed on a second semiconductor chip or a dummy chip covering an optical coupling region to correct light input into the optical coupling region for optical coupling. The material of the second semiconductor chip or the dummy chip covering the optical coupling region is transparent to light of a predetermined wavelength. The microlens can focus light incident on it onto the optical coupling interface, significantly lowering the requirements for subsequent optical coupling precision. It also improves the efficiency of the surface coupling process and increases the tolerance for placement alignment errors of die attach equipment.