BSI Image Sensor Wafer-Level Packaging via Laser and Blade Cutting
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Solution Overview
Problem
BSI image sensors face issues with cracking of the interconnection layer and reliability due to the brittleness of low dielectric constant materials and stress in the thin silicon layer during existing wafer-level packaging processes, leading to performance and reliability concerns.
Innovation Solution
A wafer-level packaging method involving laser cutting to separate interconnect layers, followed by forming insulative layers and using a blade for further cutting to minimize damage and stress on the interconnect and transparent substrate, thereby preventing cracking and exposure to air.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing wafer-level packaging process is used to cut BSI image sensors, then independent sensors can be obtained, but the interconnection layer cracks and reliability decreases due to brittleness of low dielectric constant material
Solution Approach 1:
The cutting process is divided into two distinct stages: first laser cutting to separate adjacent sensors without damaging the interconnection layer, then blade cutting to complete the separation. This segmentation of the cutting operation allows each method to be optimized for its specific function, preventing cracks while achieving sensor separation.
Solution Approach 2:
Laser cutting is performed as a preliminary action before blade cutting to pre-separate the interconnection layer and create a stress-free path. This preliminary action removes the brittle material in advance, so that subsequent blade cutting does not cause cracking in the remaining interconnection structures.
2Reliability
If thin silicon layer stress is not well released, then manufacturing can proceed, but reliability becomes poor
Solution Approach 1:
The laser cutting process extracts and removes the thin silicon layer material along the cutting path, taking out the stress concentration points. By removing material selectively, the stress in the remaining thin silicon layer is redistributed and released, preventing reliability issues.
3Reliability
If thin silicon layer is exposed to air, then cutting can be performed, but reliability is greatly decreased
Solution Approach 1:
The laser cutting process creates a localized environment that protects the thin silicon layer from air exposure during cutting. The rapid heating and melting by laser occurs faster than oxidation can proceed, and the subsequent blade cutting follows the already-created path, minimizing overall air exposure of the sensitive thin silicon layer.
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 method significantly reduces damage to the interconnect and transparent substrate, enhancing the reliability and performance of BSI image sensors by preventing cracking and water vapor erosion.
Implementation Method 1
cutting the wafer package body by laser in a first cutting process to separate the interconnect layer of adjacent BSI image sensors
Data Source
AI summary
A wafer-level packaging method of BSI image sensors includes the following steps: S1: providing a wafer package body comprising a silicon base, an interconnect layer, a hollow wall and a substrate; S2: cutting the wafer package body via laser in a first cutting process to separate the interconnect layer of adjacent BSI image sensors; and S3: cutting the wafer package body via a blade in a second cutting process to obtain independent BSI image sensors. As a result, damage of the interconnect layer and the substrate may be decreased to improve performance and reliability of the BSI image sensor.