Glass Via Formation Using Double-Sided Etching to Limit Undercut
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Solution Overview
Problem
Conventional single-sided wet etching processes for forming vias in glass substrates result in large undercutting or laterally-etched regions and limited via density due to the dependence of opening diameters on substrate thickness.
Innovation Solution
A double-sided opening process followed by a single-sided opening process, where the double-sided process enlarges openings at both ends of a damage track to form an hourglass-shaped via, and the single-sided process further enlarges the opening on the exposed surface while moving the waist of the via closer to the sealed surface, resulting in a conical frustum or trumpet-shaped via.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single-sided wet etching process is used to form vias in glass substrates, then the via can be formed through the substrate, but large undercutting or laterally-etched regions are created and via density is limited
Solution Approach 1:
The via formation process is segmented into three distinct stages: (1) forming a damage track through the substrate, (2) performing a first wet etch to create openings at both surfaces, and (3) performing a second wet etch to enlarge only the top opening. This segmentation allows independent control of different via dimensions, enabling precise shape control while minimizing undercutting at the bottom interface.
Solution Approach 2:
The damage track is formed in advance through the entire substrate thickness before any wet etching begins. This preliminary action creates a predefined pathway that guides subsequent etching processes, ensuring that the via follows the desired trajectory and reducing uncontrolled lateral etching at the bottom interface.
2Manufacturing precision
If a single-sided wet etching process is used, then the via can be formed, but the top opening diameter is dependent on substrate thickness which limits via density
Solution Approach 1:
The invention changes the etching parameters by performing two separate wet etching processes with different durations and conditions. The first etch creates initial openings at both surfaces, while the second etch selectively enlarges the top opening. This parameter change decouples the top opening diameter from substrate thickness, allowing higher via density while maintaining precise diameter control.
Solution Approach 2:
The via formation is segmented into distinct etching stages that independently control different dimensions. The first wet etch stage controls the bottom opening and via depth, while the second wet etch stage controls the top opening diameter. This segmentation breaks the direct dependency between top opening size and substrate thickness, enabling higher via density.
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 improves control over via shape and size, reduces the presence of undercutting, and allows for higher via density by decoupling the top opening diameter from the substrate thickness.
Implementation Method 1
the through-holes to be filled with conductive material can be formed by a variety of methods, including lithography of photolithographic glass, sand-blasting, electric discharge drilling, swift heavy ion tracks, and many versions of laser drilling. In others, the positions of the vias are established by a method which creates a damage track or preformed opening or pilot hole in the glass, while a subsequent wet etching process enlarges the damage track to create a through-hole
Data Source
Figure 1A~1C
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AI summary
An inorganic substrate with an improved via shape and methods for facilitating formation of such improved via shape are disclosed. A double-sided opening process may be applied to an inorganic substrate to form openings at the ends of a damage track previously formed in the inorganic substrate. One side of the inorganic substrate may then be sealed, such as by being temporarily bonded to a carrier or blocking substrate, so that a single-sided opening process may be applied to the other unsealed or unblocked surface of the inorganic substrate. The single-sided opening process may enlarge at least one of the openings formed by the double-sided opening process and may enlarge a channel between the openings to form a via having an advantageous shape.