Printed Wiring Board Bump Plating Homogeneity
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Solution Overview
Problem
Conventional printed wiring boards with plating bumps face challenges in achieving sufficient connection reliability due to differences in metal composition between the underlayer and conductor pads, leading to instability in the base plating layers and subsequent bumps.
Innovation Solution
A printed wiring board design featuring a base insulating layer, conductor layer with pads, a solder resist layer with openings, and bumps with a base plating layer formed directly from the same metal as the conductor layer, along with a top plating layer of lower melting point metals like tin, ensuring stable and reliable connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an underlayer with different metal composition is used between the conductor pad and base plating layer, then the bump formation process is simplified, but the connection reliability and stability deteriorate due to metal composition differences
Solution Approach 1:
The base plating layer is formed using the same metal composition as the conductor pad (e.g., both copper), eliminating the metal composition difference that causes instability. This homogeneity ensures stable electrical and mechanical connection between the bump and conductor pad, resolving the reliability issue while maintaining manufacturing simplicity.
Solution Approach 2:
The underlayer with different metal composition (e.g., nickel or palladium) is completely removed from the structure. By extracting this intermediate layer that causes instability, the patent directly connects the base plating layer to the conductor pad with matching metal compositions, thereby improving connection reliability without complicating the manufacturing process.
2Strength
If the base plating layer uses different metal composition from the conductor pad, then adhesion to the underlayer is improved, but the overall stability and reliability of the bump connection deteriorates
Solution Approach 1:
The base plating layer and conductor pad use identical metal compositions, ensuring compositional stability throughout the connection structure. This homogeneity maintains consistent physical and chemical properties, preventing degradation over time and ensuring long-term stability of the bump connection.
Solution Approach 2:
The bump structure employs a composite plating system where the base plating layer matches the conductor pad material, and the top plating layer provides protective and solderable surfaces. This composite approach optimizes both adhesion (through material matching) and overall connection stability (through functional layering).
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 ensures high connection reliability between bumps and conductor pads, maintaining stability even when bumps of different sizes are used, by matching the metal composition of the base plating layers with the conductor layers, thus enhancing the overall performance of the printed wiring board.
Implementation Method 1
forming the base plating layer in a first opening of the openings
Implementation Method 2
forming the base plating layer in a first opening of the openings
Implementation Method 3
forming the top plating layer on the base plating layer
Implementation Method 4
forming the top plating layer on the base plating layer
Data Source
AI summary
A printed wiring board includes a base insulating layer, a conductor layer formed on the base layer and including conductor pads, an underlayer formed on one of the conductor pads and including a metal different from a metal of the conductor layer, a solder resist layer formed on the base layer such that the solder resist layer is covering the conductor layer and has openings exposing the conductor pads, and a bump formed directly on a first conductor pad of the conductor pads and including a base plating layer formed in a first opening of the openings and a top plating layer formed on the base plating layer such that a metal of the base plating layer is same as the metal of the conductor layer. The conductor pads include a second conductor pad such that the second conductor pad is the one of the conductor pads having the underlayer.