Stepped TSV Structure in Optical Sensor Modules for Reliable Interconnects
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Solution Overview
Problem
In semiconductor device modules, especially for digital optical sensors like CMOS image sensors, integrating additional circuitry such as image signal processors or ASIC dies with the optical sensor die within the same IC package poses challenges in providing effective electrical connections and packaging that protects the delicate optical surfaces while allowing for improved imaging performance in applications like ADAS and autonomous driving.
Innovation Solution
The implementation of a through-substrate via (TSV) with a stepped bottom surface that extends from the back side to the front side of the substrate, providing a physical path for electrical connections and using a glass cover with a dam material to secure it above the optically active surface area, while a redistribution layer and conductive materials ensure secure and efficient electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a through-substrate via is created with a standard flat bottom surface, then the electrical connection path is simple and manufacturing is easier, but the via cannot effectively accommodate contact pads at different depths and the electrical connection reliability is reduced
Solution Approach 1:
The via bottom surface is segmented into different elevation levels (first bottom surface and second bottom surface) to accommodate contact pads at different depths. This segmentation allows each contact pad to be connected at its optimal depth level, improving electrical connection reliability while managing the complexity through structured division.
Solution Approach 2:
The via structure transitions from a two-dimensional flat bottom surface to a three-dimensional stepped structure with multiple elevation levels. This dimensional change enables the via to accommodate contact pads at different depths vertically, providing effective electrical connections without requiring excessively long via lengths.
2Adaptability or versatility
If the substrate thickness is increased to provide more space for additional circuitry, then more circuit components can be integrated, but the electrical connection path becomes longer and signal integrity deteriorates
Solution Approach 1:
Instead of increasing substrate thickness in the vertical direction, the via structure creates multiple connection levels within the existing thickness. The stepped bottom surface provides different elevation levels for electrical connections, enabling integration of additional circuitry without extending the vertical signal path and maintaining signal integrity.
Solution Approach 2:
The via structure nests multiple functional levels within a compact vertical footprint. The first and second bottom surfaces are nested within the via structure at different depths, allowing multiple electrical connections to be accommodated without increasing the overall substrate thickness or signal path length.
3Ease of manufacture
If the via opening size is increased to improve etching access and fill reliability, then manufacturing yield improves, but the optical active area is reduced and imaging performance deteriorates
Solution Approach 1:
The via structure implements local quality variations with different opening sizes at different levels. The opening at the first bottom surface level has a different dimension than the opening at the second bottom surface level, allowing optimized etching access and fill reliability in critical areas while maintaining small overall via footprint to preserve optical active area.
Data Source
AI summary
A package includes an optical sensor die. The optical sensor die has an optically active surface area (OASA) disposed on a front side of a substrate. A glass cover is disposed above the OASA and attached to the front side the substrate by a dam material. A through-substrate via (TSV) extends from an opening at a back side of the substrate toward a front side of the substrate. The TSV has a stepped bottom surface at the front side of the substrate. The TSV provides access for electrical connections between the back side of the substrate and the front side of the substrate.