Fin-Shaped Bump Interconnect for High-Density Multilayer Wiring Boards
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Solution Overview
Problem
Conventional multilayer wiring boards face challenges in achieving high-density wiring due to the large area occupied by circular connection pads, which can obstruct wiring and fail to provide reliable electrical interconnections, especially with misalignment during stacking.
Innovation Solution
The use of fin-shaped bumps on the wiring patterns of stacked boards, which intersect and form a cross post section, eliminating the need for circular connection pads and ensuring electrical connectivity even with misalignment, by using these bumps as inter-board connection terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If circular connection pads are used for interconnecting wiring boards, then misalignment and fabrication inaccuracy can be accommodated, but the area occupied by connection pads becomes large, obstructing wiring and reducing wiring density
Solution Approach 1:
The circular connection pad is segmented into two separate fin-shaped bumps, each belonging to different wiring boards. These bumps are positioned to intersect when the boards are stacked, creating a cross post section. This segmentation allows the connection interface to be divided between the two boards, eliminating the need for a single large pad on one board and enabling closer wiring spacing.
Solution Approach 2:
The connection structure transitions from a two-dimensional circular pad layout to a three-dimensional intersecting fin-shaped bump configuration. By extending the connection interface into the vertical dimension through the stacking of boards, the horizontal area occupied by connection pads is reduced while maintaining reliable electrical interconnection.
2Adaptability or versatility
If circular connection pads of appropriate size are formed to allow for misalignment, then stacking accuracy can be compensated, but wiring routing is obstructed due to the large area occupied by connection pads
Solution Approach 1:
The connection tolerance is segmented and distributed between the two fin-shaped bumps rather than concentrated in a single large pad. Each bump maintains a compact footprint, and their intersection when stacked provides the alignment tolerance, allowing high-density wiring while accommodating stacking variations.
Solution Approach 2:
The connection structure becomes a composite of two fin-shaped bumps from different wiring boards that intersect to form a cross post section. This composite configuration combines the advantages of both boards' bump structures, achieving both compact footprint and alignment tolerance through their overlapping arrangement.
3Reliability
If conventional interconnection methods (through holes, solder bumps, Au bumps, Cu posts) are used, then electrical connections can be established, but circular connection pads are required which bottleneck high-density wiring
Solution Approach 1:
Instead of forming a large circular pad on one board and a corresponding pad on the other board, the invention inverts the approach by forming fin-shaped bumps on both boards that intersect. This inversion eliminates the need for large pads and enables compact, high-density wiring while maintaining reliable electrical connections.
Data Source
AI summary
A multilayer wiring board includes at least two wiring boards having wiring layers containing wiring patterns formed on both sides. A pair of fin-shaped bumps are formed at desired positions on wiring patterns on the surfaces facing each other, of the wiring boards, so that the bumps assume a slender shape as seen in plan view and that the bumps intersect each other. The pair of fin-shaped bumps are electrically connected to form an inter-board connection terminal. Further, an insulating layer is formed between the wiring boards, and protection films are formed to cover the entire surface except pad areas defined at predetermined positions on outer wiring layers of the wiring boards.