Wiring Substrate Pad Design for Residue Reduction
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Solution Overview
Problem
The existing wiring substrates face issues with residues forming on the wiring pattern due to high aspect ratios of solder resist openings, leading to defects in electrical connections between the substrate and semiconductor elements.
Innovation Solution
A wiring substrate design featuring a wiring layer with a first metal layer and a second metal layer, where the second metal layer covers the first metal layer and has a pad portion that is partially exposed by a shallow opening in the protective insulation layer, reducing the aspect ratio and minimizing residue formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the solder resist thickness is increased to provide better protective insulation, then the insulation performance is improved, but the aspect ratio of openings increases leading to residue formation on the wiring pattern
Solution Approach 1:
The wiring layer is segmented into two metal layers: a first metal layer embedded in the insulation layer and a second metal layer formed on the first metal layer. This segmentation allows the opening to extend only to the pad portion of the second metal layer rather than through the entire thickness, reducing the aspect ratio while maintaining insulation performance.
Solution Approach 2:
The protective insulation layer structure is modified by adding the pad portion that protrudes from the insulation layer upper surface. This dimensional change creates a stepped structure where the opening depth is reduced relative to the overall insulation thickness, thereby reducing the aspect ratio while preserving insulation effectiveness.
2Reliability
If the opening depth is increased to fully expose the wiring pattern, then the electrical connection is improved, but residue formation on the wiring pattern increases
Solution Approach 1:
The wiring layer is divided into a first metal layer and a second metal layer with a pad portion. The opening extends only to the pad portion level, not through the entire wiring structure. This segmentation allows electrical connection to be achieved at the reduced depth while preventing residue formation on deeper wiring portions.
Solution Approach 2:
The pad portion acts as an intermediary element that provides the connection interface between the opening and the wiring layer. By extending the opening only to this intermediary pad portion rather than to the full wiring layer, residue formation is minimized while electrical connection is maintained.
3Reliability
If the opening aspect ratio is reduced to minimize residue formation, then the connection reliability is improved, but the protective insulation coverage is reduced
Solution Approach 1:
The wiring structure is segmented into embedded first metal layer and protruding second metal layer with pad portion. This allows the opening to cover only the necessary pad area for connection while the rest of the insulation layer maintains full coverage, thus preserving insulation coverage while achieving low aspect ratio for reliable connection.
Solution Approach 2:
The protective insulation layer is configured with different local qualities: the main body provides full insulation coverage, while the pad portion protrudes to create a localized connection area with reduced opening depth. This local differentiation maintains overall insulation coverage while enabling low aspect ratio openings for reliable electrical connection.
Data Source
AI summary
A wiring substrate includes a wiring layer located on an insulation layer, and a protective insulation layer covering the wiring layer and the insulation layer. The protective insulation layer includes an opening that partially exposes the wiring layer. The wiring layer includes first and second metal layers. The first metal layer is located at a position corresponding to the opening and has a larger contour than the opening in a plan view. The second metal layer includes a pad portion, which covers upper and side surfaces of the first metal layer, and a wiring portion. The opening is extended in the protective insulation layer from an upper surface of the protective insulation layer to the upper surface of the pad portion by a distance that is shorter than that from the upper surface of the protective insulation layer to an upper surface of the wiring portion.