Printed Wiring Board With Recessed Pads And Conductor Posts
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Solution Overview
Problem
Existing printed wiring boards face challenges in forming wirings at a fine pitch without electrical short circuits and warpage, particularly when using solder bumps, as increased spacing between mounting pads is required to prevent short circuits, making it difficult to achieve dense wiring configurations.
Innovation Solution
A printed wiring board with a multilayer body featuring a first and second wiring layer, via conductors, and conductor posts on a metal foil, where the second conductor pads are recessed and positioned centrally, and third conductor pads are edge-mounted, allowing for fine-pitch wiring without short circuits, and a manufacturing method involving multiple base plates and bonding layers to secure and expose conductor pads and posts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If solder bumps are used to electrically connect substrates, then electrical connection is achieved, but mounting pads require increased spacing to prevent short circuits, making fine-pitch wiring difficult
Solution Approach 1:
The patent introduces conductor posts as intermediary elements between the lower substrate and upper substrate. These conductor posts are formed on the lower substrate and extend upward, serving as intermediate connection points that eliminate the need for direct solder bump connections between mounting pads. This intermediary structure allows mounting pads to be positioned closer together while maintaining reliable electrical connection and preventing short circuits.
Solution Approach 2:
The patent transitions from a planar connection approach to a three-dimensional structure by forming conductor posts that extend vertically from the lower substrate. This dimensional change allows electrical connections to be established in the vertical dimension rather than relying solely on horizontal pad spacing, enabling fine-pitch wiring while maintaining connection reliability.
2Productivity
If mounting pads are spaced closely for fine-pitch wiring, then wiring density increases, but electrical short circuits between adjacent pads become more likely
Solution Approach 1:
Conductor posts serve as isolated intermediary connection points that are spatially separated from each other, unlike continuous conductive pads. Each conductor post provides an independent electrical connection path, preventing lateral electrical flow between adjacent mounting pads. This allows mounting pads to be positioned closely together for high wiring density while the discrete conductor posts prevent electrical short circuits.
Solution Approach 2:
The patent segments the conductive path into discrete, isolated conductor posts rather than using continuous conductive pads. Each conductor post is a separate conductive element formed by plating, creating isolated electrical connection points. This segmentation prevents electrical continuity between adjacent mounting pads, enabling close spacing for high wiring density while preventing short circuits.
3Reliability
If conductor posts are formed on conductor pads, then electrical connection is established, but stress concentration may cause warpage of the substrate
Solution Approach 1:
The patent modifies the physical parameters of the conductor posts by controlling their diameter, height, and plating thickness. By optimizing these parameters, the conductor posts provide sufficient electrical connection capability while minimizing their cross-sectional area and volume. This reduces the thermal mass and stress generation during soldering processes, thereby minimizing substrate warpage while maintaining reliable electrical connection.
Solution Approach 2:
The patent applies local quality by forming conductor posts only at specific locations where electrical connection is needed, rather than using extensive conductive pads. The conductor posts are precisely positioned on conductor pads, providing localized electrical connection points. This localized approach maintains necessary electrical connectivity while minimizing the overall conductive material present, thereby reducing stress concentration and substrate warpage.
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 the formation of wirings at a fine pitch while preventing electrical short circuits and warpage, improving connection reliability and inspection accuracy by dispersing stress and using recessed pads to restrict solder flow.
Implementation Method 1
fixing a metal foil having a carrier copper foil to a first base plate
Implementation Method 2
the bonding layer attaches the second base plate to the first main surface of the multilayer body
Implementation Method 3
conductor posts each including a plating material and formed on the third conductor pads
Data Source
AI summary
A printed wiring board includes a multilayer body, a first wiring layer formed on first surface of the body and including first pads, a second wiring layer embedded into second surface of the body and including second and third pads, conductor posts formed on the third pads, and via conductors formed in the body and having diameter reducing toward the second surface of the body. Each third pad has metal foil formed thereon such that each post is formed on the foil, the second wiring layer is formed such that the second pads are positioned to connect an electronic component in central portion of the second surface of the body and the third pads are positioned to connect another board in outer edge portion of the second surface of the body, and the second pads are formed such that each second pad has exposed surface recessed from the second surface.