Deformable Anodic Bonding Electrode for Void-Free Wafer Sealing
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Solution Overview
Problem
Conventional anodic bonding apparatuses face issues with void formation due to air inclusion and partial contact of electrodes, leading to substrate breakage and reliability concerns in bonding electrically conductive substrates like silicon wafers with glass substrates.
Innovation Solution
An anodic bonding apparatus with a deformable stainless steel alloy thin plate forming a diaphragm structure, allowing for stepless adjustment of contact area and air pressure to expel air concentrically from the center to the edges, preventing voids and partial contact-induced breakage by matching the swelling tip with the laminate's central portion and controlling pressure differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If anodic bonding is carried out in the atmosphere, then the bonding process is simple, but air enters the bonding surface causing voids
Solution Approach 1:
The patent applies vacuum environment (inert atmosphere principle) to eliminate air from the bonding interface. By performing anodic bonding under vacuum conditions, air is removed from the bonding surface, preventing void formation while maintaining bonding effectiveness. This resolves the contradiction by replacing atmospheric bonding with vacuum bonding.
2Device complexity
If the upper electrode is pressed against the substrate with fixed contact area, then the electrode structure is simple, but partial contact causes substrate breakage
Solution Approach 1:
The patent employs a deformable upper electrode that can dynamically adjust its contact area with the substrate. The electrode transitions from point contact to distributed contact as pressure is applied, ensuring uniform pressure distribution across the bonding surface. This dynamic adaptation prevents localized stress concentration that would cause substrate breakage, while maintaining structural simplicity.
Solution Approach 2:
The patent changes the physical state of the upper electrode from rigid to deformable, allowing it to adapt its contact parameters (contact area, pressure distribution) to match the substrate surface. This parameter adaptation ensures complete surface contact without exceeding substrate strength limits, preventing breakage while maintaining bonding reliability.
3Productivity
If air is not expelled from the bonding surface, then the bonding process is fast, but voids occur due to air inclusion
Solution Approach 1:
The patent applies vacuum treatment before the actual bonding process to preliminarily remove air from the bonding interface. By pre-evacuating the bonding chamber and ensuring air is expelled from between substrates before applying bonding pressure and voltage, the process prevents void formation without significantly extending the overall bonding time. This preliminary air removal action ensures void-free bonding while maintaining productivity.
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
Enables void-free, reliable bonding of electrically conductive and glass substrates by expelling air from the center to the edges and preventing partial contact, thus ensuring uniform bonding and substrate integrity.
Implementation Method 1
the inside of the container is evacuated, and the upper electrode is moved downward, the tip which has swollen in a convex form of the electrically conductive metal thin plate first comes in contact with the central portion of the laminate
Implementation Method 2
proceed with anodic bonding while expelling air which may cause voids concentrically from the center portion toward the outer edge
Implementation Method 3
a direct current voltage is applied such that the electrically conductive substrate is an anode and such that the glass substrate is a cathode, thereby to bond the electrically conductive substrate and the glass substrate
Implementation Method 4
the inside of a container is evacuated
Data Source
Figure 1~2
Figure 3
Figure 4A~4B
AI summary
The present invention provides an anodic bonding apparatus 1, 1 b for bonding a laminate including an electrically conductive substrate 3 and a glass substrate 4, the anodic bonding apparatus including: a container 2 of which pressure is capable of being reduced; an upper electrode 11 disposed in the container and configured in a movable manner in the vertical direction so as to contact to and separate from the laminate, and the upper electrode including: a main body part 13; an electrically conductive metal thin plate 12 to be contacted with the laminate; and a space part 15, between the main body part and the electrically conductive metal thin plate, into and from which a fluid is supplied and drained, wherein the electrically conductive metal thin plate has a diaphragm structure being capable of deforming based on a pressure difference between the space part and the inside of the container, the electrically conductive metal thin plate 12 is positioned at the main body part so as to swell in a convex form in the direction to the laminate when the space part is higher in pressure than the inside of the container; and a lower electrode 10, wherein the electrically conductive substrate and the glass substrate is bonded by: interposing the laminate between the upper electrode and the lower electrode; heating the laminate; and applying a direct current voltage to the laminate such that the electrically conductive substrate is an anode and the glass substrate is a cathode.