Flip-Chip Mounting Sealing Strategy for Image Sensor Reliability
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Solution Overview
Problem
The challenge is to enhance the reliability of solid-state image pickup devices by addressing the insufficient mounting strength and sealing material flow issues during flip-chip mounting on flexible substrates, which affects the thickness reduction and manufacturing yield in mobile devices.
Innovation Solution
A manufacturing method involving a flexible wiring substrate with a specific layout of bump electrodes, where sealing material is strategically applied and cured to reinforce the mounting strength, and additional sealing material is injected between the sensor chip and substrate to prevent material flow and ensure the sensor surface's integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If direct flip-chip mounting is used to reduce thickness, then device thickness is reduced, but mounting strength becomes insufficient
Solution Approach 1:
A sealing material is introduced as an intermediary substance between the solid-state image pickup element and the flexible substrate. This sealing material serves dual purposes: it provides mechanical support to enhance mounting strength while simultaneously sealing the space between the element and substrate to prevent material flow during the flip-chip mounting process.
Solution Approach 2:
The physical state of the sealing material is changed from liquid (before curing) to solid (after curing) through heat treatment. This parameter change allows the sealing material to transition from a flowable state during mounting to a rigid state that provides structural support and enhances mounting strength after the process.
2Strength
If sealing material is applied to enhance mounting strength, then mounting strength is improved, but sealing material flows onto sensor surface degrading reliability
Solution Approach 1:
The sealing material is applied in advance to the flexible substrate at positions strategically designed to prevent flow toward the sensor surface. This preliminary application ensures that when heating occurs during flip-chip mounting, the sealing material is already in position to contain any potential flow and protect the sensor surface from contamination.
Solution Approach 2:
The sealing material is applied non-uniformly across the substrate surface, with specific regions receiving sealing material and others remaining clear. This local quality approach ensures adequate sealing and mounting strength in critical areas while maintaining an open, contamination-free sensor surface area.
3Strength
If heat is applied to cure sealing material, then mounting strength is improved through curing, but substrate bending occurs causing material flow
Solution Approach 1:
A protective film is applied to the flexible substrate to provide structural reinforcement during the heating and curing process. This film prevents excessive bending and deformation of the thin flexible substrate when heat is applied, thereby preventing the substrate shape changes that would cause sealing material to flow onto the sensor surface.
Solution Approach 2:
The protective film serves as a pre-applied cushioning layer that restrains the flexible substrate from bending excessively during heat treatment. This beforehand cushioning prevents the substrate from deforming into a shape that would cause the sealing material to flow toward and contaminate the sensor surface.
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 improves the mounting strength and reliability of the solid-state image pickup device, preventing sealing material flow onto the sensor surface and enhancing manufacturing yield by controlling the sealing material's application and curing processes.
Implementation Method 1
curing this sealing material by heat at the time of flip-chip mounting
Implementation Method 2
due to the influence of the heat generated at the time of flip-chip mounting, the phenomenon that a part of the film-shaped substrate is bent occurs
Data Source
AI summary
After a wiring substrate having, on its lower surface, an opening and terminals arranged therearound is provided, a sealing material is supplied to the lower surface of the wiring substrate, and a sensor chip is flip-chip mounted on the lower surface of the wiring substrate. The sensor chip has, on its front surface, a sensor surface and bump electrodes, and each bump electrode is thermocompression-bonded onto each terminal of the wiring substrate and the sensor surface is exposed from the opening. The sensor chip has, in its outer peripheral portion of the front surface, a first region where the bump electrodes are arranged and a second region where no bump electrode is arranged. The sealing material is supplied to a region planarly overlapped with the first region when the sensor chip is mounted later, and no sealing material is supplied to a region planarly overlapped with the second region.