COG Image-Capturing Unit Thermal Stress Reduction
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Solution Overview
Problem
The existing COG image-capturing units face warping issues due to thermal expansion, causing stress on bumps and potential damage, especially when the transparent substrate and image-capturing chip are heated or cooled.
Innovation Solution
An image-capturing unit with a COG structure that includes a backside illumination MOS image sensor, a transparent substrate, a mounting substrate with a lower linear expansion coefficient, and a heat releasing member, where the mounting substrate is interposed between the image-capturing chip and the transparent substrate to reduce stress on bumps, and the heat releasing member contacts both the image-capturing chip and the signal processing chip to enhance thermal management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the transparent substrate and image-capturing chip are directly connected using flip-chip implementation, then the COG structure is achieved, but warping occurs during heating or cooling causing stress on bumps and potential damage
Solution Approach 1:
A mounting substrate is introduced as an intermediary component between the transparent substrate and the image-capturing chip. This mounting substrate has a linear expansion coefficient that is lower than both the transparent substrate and the image-capturing chip, serving as a buffer to reduce thermal expansion mismatch and the resulting warping stress on the bumps during temperature changes.
Solution Approach 2:
The linear expansion coefficient parameter is strategically selected for the mounting substrate to be lower than both the transparent substrate and the image-capturing chip. By changing this material parameter, the patent creates a gradient structure that progressively accommodates thermal expansion differences, reducing warping stress while maintaining the COG structure.
2Reliability
If the mounting substrate with lower linear expansion coefficient is interposed between the image-capturing chip and transparent substrate, then stress on bumps is reduced, but device structure becomes more complex
Solution Approach 1:
The mounting substrate serves multiple functions simultaneously: it provides mechanical support for the image-capturing chip, acts as a thermal management interface through the heat releasing member, and functions as a stress buffer due to its specific linear expansion coefficient. This multi-functionality justifies the additional structural layer by consolidating several critical roles into a single component.
3Temperature
If heat releasing member contacts both image-capturing chip and signal processing chip, then thermal management is enhanced, but manufacturing process becomes more complex
Solution Approach 1:
The heat releasing member is designed to contact both the image-capturing chip and the signal processing chip simultaneously, merging the thermal management function into a single integrated component rather than using separate heat sinks for each chip. This consolidation simplifies the overall thermal management system while effectively dissipating heat from multiple heat-generating components.
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 configuration reduces stress on bumps and improves heat transfer efficiency, minimizing dark current and image quality degradation by maintaining thermal balance and reducing the need for complex processing steps.
Implementation Method 1
when the transparent substrate and the image-capturing chip are heated or cooled, warping occurs in the image-capturing chip. As a result, this warping causes stress in the bumps
Implementation Method 2
the heat releasing member contacts both the image-capturing chip and the signal processing chip to enhance thermal management
Data Source
Figure 1
Figure 2
Figure 3A~3E
AI summary
Provided is an image-capturing unit including an image-capturing chip that includes a first surface having a pixel and a second surface that is on an opposite side of the first surface and has provided thereon an output section that outputs a pixel signal read from the pixel; a transparent substrate that is arranged facing the first surface and includes a wire pattern; a mounting substrate that is arranged facing the second surface and supports the image-capturing chip; and a relay section that is arranged on the mounting substrate and relays, to the wire pattern, the pixel signal output from the output section. Also provided is an image-capturing apparatus including the image-capturing unit described above.