Copper Plating Layer Kirkendall Void Suppression
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Solution Overview
Problem
The formation of Kirkendall voids at the bonding interface between copper and tin or tin alloys in electronic components reduces the reliability of the structure, and existing solutions either complicate the metal composition or increase production costs.
Innovation Solution
A copper plating layer or copper alloy plating layer is formed through an electroplating process with a prescribed first cathode current density followed by a change to a lower second cathode current density, creating a surface layer with a thickness of 0.05 μm to 15 μm, which suppresses the formation of Kirkendall voids without complex steps or significant cost increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a diffusion barrier layer containing nickel or nickel-phosphorus is formed on a copper-containing pillar layer to suppress Kirkendall void formation, then reliability is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The invention changes the cathode current density parameter during electroplating, specifically using a two-stage process where the current density is reduced in the final stage. This parameter modification alters the diffusion characteristics at the Cu-Sn interface, suppressing Kirkendall void formation without requiring additional barrier layers or complex multi-step processes.
Solution Approach 2:
The invention performs preliminary action by controlling the electroplating conditions in advance to prevent Kirkendall void formation. By adjusting the cathode current density during the plating process, the diffusion barrier effect is achieved proactively during manufacturing rather than requiring post-processing or additional protective layers.
2Reliability
If complex metal composition control is implemented to suppress Kirkendall void formation, then reliability is improved, but ease of manufacture deteriorates
Solution Approach 1:
Instead of controlling complex metal compositions, the invention simplifies manufacturing by changing only the cathode current density parameter during electroplating. This single parameter control achieves Kirkendall void suppression while maintaining ease of manufacture, as current density adjustment is a straightforward electroplating process variable.
3Reliability
If additional plating steps are added to suppress Kirkendall voids, then reliability is improved, but productivity decreases
Solution Approach 1:
The invention merges the Kirkendall void suppression function into the existing electroplating process itself. By incorporating cathode current density control within the standard plating step, the solution eliminates the need for separate additional plating steps, thereby maintaining high productivity while achieving improved reliability.
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
This approach effectively suppresses Kirkendall void formation, enhancing the reliability of the structure while maintaining a straightforward production process and controlling costs.
Implementation Method 1
performing an electroplating process at a prescribed first cathode current density by using a copper or copper alloy electroplating bath
Implementation Method 2
performing an electroplating process at a prescribed first cathode current density by using a copper or copper alloy electroplating bath
Implementation Method 3
a difference in diffusion speed among these metals may form a Kirkendall void
Data Source
AI summary
A structure includes a copper or copper alloy plating layer, in which Kirkendall void formation is suppressed. The copper or copper alloy plating layer is formed by electroplating at a prescribed first cathode current density by using a copper or copper alloy electroplating bath and then completing the electroplating after the first cathode current density is changed to a lower second cathode current density. The first cathode current density is a single cathode current density in the electroplating at this current density or an average cathode current density in the electroplating by combining plural cathode current densities. The first cathode current density is at lowest 5 A/dm2. A layer formed by changing the first cathode current density to the second cathode current density is a surface layer part of the copper or copper alloy plating layer, which can have a thickness of 0.05 μm to 15 μm.