Solid-State Imaging Device Electrode Pad Stress Mitigation
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Solution Overview
Problem
Solid-state imaging devices face damage due to stress concentration on electrode pads caused by thermal expansion during manufacturing processes, leading to potential disconnection and reduced reliability.
Innovation Solution
Incorporating a protective film made of inorganic insulating material between the semiconductor substrate and the sealant, which reduces stress concentration on the electrode pad, and optionally increasing the thickness of the electrode pad relative to the underside wiring material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a thin Al film electrode pad is used on the semiconductor substrate, then the device structure is simple and manufacturing is easy, but the electrode pad is susceptible to stress concentration and detachment during thermal processes
Solution Approach 1:
The patent applies composite materials by creating a multi-layer structure consisting of the Al film electrode pad, inorganic insulating material layer, and organic insulating material layer. This composite structure protects the thin Al film from stress concentration during thermal processes while maintaining ease of manufacture through standard layering techniques.
Solution Approach 2:
The patent implements beforehand cushioning by placing the inorganic insulating material layer between the Al film electrode pad and the organic insulating material layer before thermal processing. This layer acts as a stress buffer that prevents direct transmission of thermal stress to the thin Al film, thereby preventing detachment while maintaining manufacturing simplicity.
2Device complexity
If the sealant is placed directly on the electrode pad, then the bonding structure is simple, but stress concentration occurs on the electrode pad during thermal expansion
Solution Approach 1:
The patent introduces an inorganic insulating material layer as an intermediary between the Al film electrode pad and the organic insulating material layer (sealant). This intermediary layer has appropriate mechanical and thermal properties that buffer stress transmission, preventing stress concentration on the electrode pad while maintaining reasonable device complexity through a straightforward layering approach.
3Reliability
If the electrode pad is sandwiched between sealant and underside wiring, then electrical connection is achieved, but stress concentration causes crack formation and detachment during reflow soldering
Solution Approach 1:
The patent applies beforehand cushioning by placing the inorganic insulating material layer between the Al film electrode pad and the organic insulating material layer before the reflow soldering process. This layer serves as a stress buffer that prevents thermal stress from concentrating on the electrode pad during heating and cooling cycles, thereby preventing crack formation and detachment while maintaining electrical connection functionality.
Solution Approach 2:
The patent uses composite materials by creating a multi-layer structure with the Al film electrode pad, inorganic insulating material layer, and organic insulating material layer. This composite structure provides both mechanical protection against stress concentration and electrical insulation, maintaining reliability while adding only moderate complexity to the device structure.
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
Prevents detachment of the electrode pad and underside wiring, enhancing the reliability and yield rate of solid-state imaging devices by mitigating stress-induced damage during heat treatment steps.
Implementation Method 1
the sealant 21 may flow and thus cause stress concentration on the electrode pad 12. This stress concentration on the electrode pad 12 can cause a crack D1 to form in the insulating film 13 having a coefficient of linear expansion that differs from that of a metallic material constituting the underside wiring 16
Data Source
AI summary
A solid-state imaging device includes a semiconductor substrate having a foreside provided with an imaging area and an electrode pad, the imaging area having an array of optical sensors, the electrode pad being disposed around a periphery of the imaging area; a transparent substrate joined to the foreside of the semiconductor substrate with a sealant therebetween; underside wiring that extends through the semiconductor substrate from the electrode pad to an underside of the semiconductor substrate; and a protective film composed of an inorganic insulating material and interposed between the semiconductor substrate and the sealant, the protective film covering at least the electrode pad.