Inclined Via Structure for Flexible Substrates
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Solution Overview
Problem
Existing via structures in multi-layer substrates, particularly in flexible substrates, face issues with peeling or breaking when bent, leading to increased via land size and reduced routing density due to manufacturing limitations of etching and semi-additive methods, which cannot satisfy the demands of high integration products.
Innovation Solution
A via structure with an inclined wall and a second metal layer formed inside the via using a metal lift-off process, where the via land is smaller than the via diameter, enhancing adhesion and pliability, and allowing for precise definition of via land size through photolithography, thereby reducing manufacturing tolerances and increasing routing density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the via land size is increased to prevent peeling and breaking in bent areas, then the reliability is improved, but the routing density decreases
Solution Approach 1:
The patent applies curvature by forming an inclined wall inside the via hole instead of using a vertical via wall. This inclined geometry distributes stress more effectively during bending, preventing peeling and breaking at the via land connections while maintaining smaller via land dimensions, thus resolving the contradiction between reliability and routing density
Solution Approach 2:
The patent changes the geometric parameters of the via structure by creating an inclined wall with a specific angle and positioning the via land at a lower level than the top surface of the dielectric layer. This parameter modification allows the via land to be smaller than in conventional structures while maintaining structural integrity during bending, thereby increasing routing density without sacrificing reliability
2Manufacturing precision
If the via land size is increased to accommodate manufacturing tolerances, then the manufacturing precision is improved, but the routing density decreases
Solution Approach 1:
The inclined wall geometry provides a gradual transition zone that is more tolerant to manufacturing variations. The slanted surface accommodates slight deviations in via hole positioning and size while maintaining proper metal layer connections, reducing the need for oversized via lands and enabling finer pitch designs
Solution Approach 2:
The patent performs preliminary actions by pre-forming the inclined wall structure before final via land formation. This preliminary geometric preparation ensures that subsequent manufacturing steps can proceed with tighter tolerances, as the inclined structure already provides stress distribution and alignment guidance, enabling precise via land sizing
3Productivity
If the via structure is made finer to increase routing density, then the productivity is improved, but the reliability deteriorates due to higher peeling risk
Solution Approach 1:
The inclined wall provides a curved/angled stress distribution path that is particularly effective for fine-pitch vias. This geometry prevents stress concentration at sharp corners and vertical interfaces, making fine-pitch via structures resistant to peeling and breaking despite their small dimensions, thus enabling high routing density without reliability loss
Solution Approach 2:
The patent modifies key geometric parameters including the inclined wall angle, via land position, and via hole diameter to optimize the balance between fineness and reliability. These parameter adjustments allow via structures to be made smaller for higher density while the optimized geometry maintains structural integrity during bending operations
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
The solution effectively minimizes the size of via lands and metal lines, increasing routing density and reliability in flexible substrates, while maintaining electrical connectivity and pliability, even in frequently bended areas, thus addressing the limitations of prior methods.
Implementation Method 1
proceeding a photolithography process to the photoresist layer
Implementation Method 2
the second metal layer formed on the dielectric layer by a metal lift-off process
Data Source
AI summary
Disclosed is a via structure in a multi-layer substrate, comprising a first metal layer, a dielectric layer and a second metal layer. The first metal layer has an upper surface. The dielectric layer covers the first metal layer in which a via is opened to expose the upper surface. The second metal layer is formed in the via and contacts an upper surface and an inclined wall of the via. A contacting surface of the second metal layer has a top line lower than the upper edge of the inclined wall. Alternatively, the second metal layer can be formed on the dielectric layer as being a metal line simultaneously as formed in the via as being a pad. The metal line and the pad are connected electronically. The aforesaid metal second layer can be formed in the via and on the dielectric layer by a metal lift-off process.