Imaging Element Package Sealing to Limit Sensor Warpage
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Solution Overview
Problem
The warpage of imaging element chips due to the bimetal effect, caused by differences in linear expansion coefficients of components, affects the flatness of the light receiving surface and image quality, particularly in large-sized imaging element chips, which existing technologies do not adequately address.
Innovation Solution
An imaging element unit is fixed to a circuit board through a conductive member with a fixing member having a linear expansion coefficient smaller than the circuit board, and sealed by a sealing member with an adhesive having a Young's modulus of 500 MPa or more, or less than 500 MPa with a thickness of 15 μm or less, to prevent warpage by distributing stress effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the package is mounted on the circuit board through soldering at high temperature, then electrical connection is achieved, but warpage occurs due to bimetal effect from linear expansion coefficient differences
Solution Approach 1:
The patent changes the physical parameters of the adhesive material, specifically selecting materials with appropriate linear expansion coefficients that match or compensate for the circuit board and imaging element chip. This parameter matching reduces the bimetal effect and resulting warpage while maintaining reliable electrical connection through the mounting process.
Solution Approach 2:
The patent introduces an adhesive layer as an intermediary substance between the imaging element chip and the circuit board. This adhesive mediator absorbs and compensates for the thermal expansion differences, preventing direct stress transmission that would cause warpage, while still enabling electrical connection through the assembly.
2Measurement precision
If the imaging element chip size is increased, then imaging resolution is improved, but warpage due to bimetal effect becomes more severe
Solution Approach 1:
The patent applies parameter matching by selecting adhesive materials whose linear expansion coefficients are specifically chosen to compensate for the larger chip size effects. The adhesive layer thickness and material properties are adjusted as parameters to maintain flatness across larger imaging element chip areas, enabling high-resolution imaging without excessive warpage.
3Shape
If a rigid adhesive is used to prevent warpage, then flatness is improved, but stress concentration may occur
Solution Approach 1:
The patent optimizes the adhesive layer thickness as a critical parameter. By controlling the thickness within specific ranges, the adhesive provides sufficient rigidity to maintain flatness and prevent warpage, while the limited thickness prevents excessive stress concentration. This parameter control achieves the balance between shape stability and stress distribution.
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 solution effectively reduces warpage of the imaging element chip to maintain image quality, as demonstrated by simulation results showing warpage suppression to 60 μm or less at 80% image height, even with large-sized sensors, by using high-rigidity adhesives or thin, low-rigidity adhesives strategically.
Implementation Method 1
the sealing member and the wall portion are fixed by an adhesive having a Young's modulus of 500 MPa or more
Implementation Method 2
a warpage due to a bimetal effect occurs due to a difference in linear expansion coefficients of components of the unit
Data Source
AI summary
A package includes a flat portion to which an imaging element chip is fixed, a wall portion surrounding a fixed surface of the imaging element chip in the flat portion, and a plurality of first terminals electrically connected to the imaging element chip. A protective cover seals the imaging element chip in a state where the protective cover overlaps the wall portion. A conductive member is provided between the first terminal exposed from a rear surface of the package and a second terminal formed on a circuit board disposed to face the rear surface of the package to fix the package and the circuit board and electrically connect the first terminal and the second terminal to each other. The protective cover and the wall portion are fixed by an adhesive having a Young's modulus of 500 MPa or more.