Printed Wiring Board Metal Bump Adhesion via Segmented Pad Design
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Solution Overview
Problem
Existing printed wiring boards face challenges in forming metal bumps with uniform heights and reliable connections, as single-metal pads are difficult to achieve uniform heights and reliable connections when forming metal bumps.
Innovation Solution
A printed wiring board design featuring a copper layer with a Ni film, a Pd film, and an Au film, where the copper layer is reduced in diameter towards the upper surface, and the Ni film fills spaces between the copper layer and cylindrical sidewalls of the resin insulating layer, ensuring the copper layer does not contact the sidewalls and forming metal bumps with increased connection reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-metal pad structure is used, then the manufacturing process is simple, but the metal bumps cannot achieve uniform heights and reliable connections
Solution Approach 1:
The pad structure is segmented into multiple metal layers (first metal layer, second metal layer, third metal layer) with different functions. The first metal layer provides adhesion to the resin insulating layer, the second metal layer forms the bump base, and the third metal layer provides surface protection and solderability. This segmentation allows each layer to be optimized independently, achieving uniform bump heights and reliable connections while maintaining manufacturing feasibility through sequential deposition processes.
Solution Approach 2:
The invention uses a composite multi-layer metal pad structure instead of a single-metal pad. Each layer is made of different metals with specific properties (e.g., copper for conductivity, nickel for adhesion, gold for surface protection). This composite structure combines the advantages of different materials to achieve both manufacturing precision (uniform bump heights) and connection reliability, while the overall manufacturing process remains relatively simple through standard deposition techniques.
2Device complexity
If a single-metal pad structure is used, then the structure is simple, but connection reliability is poor
Solution Approach 1:
The pad is divided into multiple functional metal layers where each layer serves a specific purpose: the first metal layer ensures strong adhesion to the resin insulating layer, the second metal layer provides the bump foundation with good conductivity, and the third metal layer offers surface protection and solderability. This functional segmentation significantly improves connection reliability by addressing multiple requirements simultaneously, while the structure remains manageable through systematic layer-by-layer construction.
Solution Approach 2:
The multi-layer metal pad employs composite materials with complementary properties. For example, copper or aluminum provides excellent electrical conductivity, nickel or palladium offers superior adhesion and oxidation resistance, and gold provides corrosion resistance and solderability. This composite approach enhances connection reliability by combining the strengths of different materials, while the overall device complexity is controlled through standardized manufacturing processes.
3Ease of manufacture
If the copper layer contacts the cylindrical sidewalls directly, then the manufacturing process is simpler, but the adhesion and reliability of metal bumps are reduced
Solution Approach 1:
The space between the copper layer and cylindrical sidewalls is segmented and filled with a Ni film that acts as an adhesive bridge. This Ni film creates a transition zone that mechanically and chemically bonds the copper layer to the resin insulating layer sidewalls, significantly improving adhesion. The filling process can be achieved through electroplating or electroless plating, maintaining manufacturing simplicity while dramatically enhancing metal bump reliability.
Solution Approach 2:
The Ni film serves as an intermediary material between the copper layer and the resin insulating layer sidewalls. This intermediate layer provides excellent adhesion to both materials, creating a strong bond that prevents delamination and improves bump reliability. The Ni film fills the gap and creates a gradual transition, allowing stress distribution and preventing direct contact between copper and resin, which would otherwise result in poor adhesion.
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 allows for the formation of metal bumps with uniform heights and enhanced connection reliability, as the Ni film fills spaces between the copper layer and the resin insulating layer, improving the adhesion and reliability of the metal bumps.
Implementation Method 1
the Ni film is filling spaces between the copper layer and the cylindrical sidewalls of the outermost resin insulating layer
Data Source
AI summary
A printed wiring board includes resin insulating layers including an outermost resin insulating layer, conductor layers laminated on the resin insulating layers, a copper layer formed in the outermost insulating layer, and metal bumps formed on the copper layer such that the bumps have upper surfaces protruding from the outermost insulating layer and that each metal bump includes Ni film, Pd film and Au film. The copper layer is reduced in diameter toward upper surface side such that the copper layer has upper and bottom surfaces and each upper surface has diameter that is smaller than diameter of each bottom surface, the outermost insulating layer has cylindrical sidewalls formed such that at least part of the copper layer is not in contact with the sidewalls, and the bumps are formed such that the Ni film is filling spaces between the copper layer and the sidewalls of the outermost insulating layer.