Copper Bump Sidewall Protection Against Galvanic Corrosion
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Solution Overview
Problem
The packaging of semiconductor devices faces failure modes due to Galvanic corrosion, particularly at the first-level interconnects, leading to missing bumps and over-etched bumps, which increases yield loss and assembly costs.
Innovation Solution
Applying a nickel-palladium-gold (NiPdAu) surface finish to the top surface and sidewalls of copper bumps to protect against Galvanic corrosion, ensuring no exposed copper and enhancing solder joint reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a copper bump is used for interconnect, then electrical conductivity is improved, but Galvanic corrosion occurs due to potential difference with gold pads leading to missing bumps
Solution Approach 1:
A nickel-palladium-gold (NiPdAu) surface finish is applied as an intermediary protective layer between the copper bump and the corrosive environment. This surface finish acts as a barrier that prevents direct contact between copper and electrolytes, eliminating the Galvanic corrosion mechanism while maintaining electrical conductivity of the copper underlying structure.
2Ease of manufacture
If electroless Cu removal is used to reduce costs, then assembly cost is reduced, but yield loss increases to roughly 100% due to Galvanic corrosion
Solution Approach 1:
The NiPdAu surface finish is applied in advance to the copper bumps before the electroless Cu removal process. This preliminary protective action ensures that even when copper is removed or corroded during subsequent processing, the critical interconnect structure remains protected, preventing the 100% yield loss that would otherwise occur.
3Reliability
If Cu bump is connected to Au-terminated pads, then electrical interconnect is achieved, but missing bumps occur due to potential difference between Cu and Au
Solution Approach 1:
The NiPdAu surface finish serves as a mediator between the copper bump and the gold-terminated pads. This intermediate layer prevents direct electrochemical interaction between dissimilar metals (Cu and Au), thereby eliminating the Galvanic corrosion that would otherwise cause missing bumps while maintaining the electrical interconnect function.
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 significantly reduces yield loss and FLI failure modes associated with missing and over-etched bumps, while maintaining assembly efficiency and cost-effectiveness.
Implementation Method 1
failure modes at the various interconnect levels (e.g., at a first-level interconnect (FLI)). These failure modes are typically associated with missing bumps and over-etched bumps at an interconnect level due to Galvanic corrosion. Glavnic corrosion is the electrochemical process in which a metal corrodes, especially as the metal electrically contacts another metal, in the presence of an electrolyte.
Data Source
Figure 1A~1B
Figure 1C~1D
Figure 2
AI summary
Embodiments include semiconductor packages and a method of forming the semiconductor packages. A semiconductor package includes a resist layer disposed on a conductive layer. The semiconductor package also has a bump disposed on the conductive layer. The bump has a top surface and one or more sidewalls. The semiconductor package further includes a surface finish disposed on the top surface and the one or more sidewalls of the bump. The semiconductor package may have the surface finish surround the top surface and sidewalls of the bumps to protect the bumps from Galvanic corrosion. The surface finish may include a nickel-palladium-gold (NiPdAu) surface finish. The semiconductor package may also have a seed disposed on a top surface of the resist layer, and a dielectric disposed on the seed. The dielectric may surround the sidewalls of the bump. The semiconductor package may include the seed to be an electroless copper seed.