Wiring Substrate Plating Structure to Prevent Nickel Elution
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Solution Overview
Problem
The formation of a nickel layer through electroless plating on a wiring substrate results in gaps between the side surface of the nickel layer and the solder resist layer, leading to incomplete formation of palladium and gold layers, which can cause nickel elution into cleaning water and discoloration of the gold layer.
Innovation Solution
A wiring substrate design with a nickel or nickel alloy first plating layer and a second plating layer made of a metal with higher oxidation resistance, such as palladium or gold, that entirely covers the side surface of the nickel layer, preventing nickel elution into cleaning water.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If electroless plating is used to form the Ni layer, then the Ni layer can be formed on the wiring layer, but a gap is produced between the side surface of the Ni layer and the wall surface of the opening in the solder resist layer
Solution Approach 1:
The patent applies preliminary action by forming a protrusion on the wiring layer before plating. This protrusion extends into the opening of the solder resist layer and serves as a foundation for the Ni layer, ensuring that the Ni layer forms with adequate coverage and minimizes gap formation between the Ni layer side surface and the solder resist layer wall surface.
2Ease of manufacture
If the plating solution enters the gap to form the Pd layer and Au layer, then these layers can be formed, but the plating solution may be limited and the layers may not form completely on the side surface of the Ni layer
Solution Approach 1:
The protrusion is formed in advance on the wiring layer to provide a structural foundation that guides plating solution flow and ensures complete coverage of the Ni layer, including its side surfaces, during subsequent Pd and Au plating processes.
Solution Approach 2:
The protrusion acts as an intermediary structure between the wiring layer and the plating layers. It facilitates uniform plating solution distribution and ensures that the Pd and Au layers form completely and uniformly on the Ni layer side surfaces that are exposed in the gap.
3Ease of operation
If cleaning water enters the gap, then nickel may be eluted into the cleaning water due to local cell effect, but this causes contamination and discoloration of the gold layer
Solution Approach 1:
The patent converts the potential harm of gap formation into a benefit by using the protrusion structure to control and direct the gap's position and size. This controlled gap structure prevents uncontrolled Ni elution while maintaining the necessary space for complete plating layer formation, thus preventing contamination during cleaning operations.
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
Prevents nickel elution into cleaning water, maintaining the integrity and quality of the gold layer, and limiting interdiffusion of nickel and gold due to heat.
Implementation Method 1
The Ni layer may be formed through an electroless plating process
Implementation Method 2
The plating solution that enters the slight gap to form the Pd layer and the Au layer may be limited
Implementation Method 3
The second plating layer is formed from a metal having a higher resistance to oxidation than the metal forming the first plating layer
Data Source
AI summary
A wiring substrate includes a wiring layer, a protective insulation layer covering the wiring layer, an opening extending through the protective insulation layer and partially exposing an upper surface of the wiring layer, a first plating layer formed inside the opening on the wiring layer that is exposed in the opening, a gap extending between a side surface of the first plating layer and a wall surface of the opening, and a second plating layer entirely covering a surface of the first plating layer in the opening of the protective insulation layer. The first plating layer is formed from nickel or a nickel alloy. The second plating layer is formed from a metal having a higher resistance to oxidation than the metal forming the first plating layer. The second plating layer entirely covers a side surface of the first plating layer that is exposed in the gap.