Cu Pillar Bump Electrolytic Metal Sidewall Protection
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Solution Overview
Problem
Copper pillar bumps in integrated circuit fabrication face issues such as oxidation leading to poor adhesion and stress-induced delamination, along with high process costs and interface delamination in conventional sidewall protection methods, particularly in fine pitch package technologies.
Innovation Solution
A sidewall protection layer formed through an electrolytic metal plating process is applied to the copper pillar bumps, preventing oxidation and improving adhesion, which reduces process costs and eliminates undercut issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a nickel cap layer is provided on the copper pillar bump to reduce IMC thickness, then the solder joint strength is improved, but the nickel layer causes copper undercut after UBM etching, resulting in nickel layer overhanging and stress-induced delamination failures
Solution Approach 1:
The patent removes the nickel cap layer from the copper pillar bump structure. By extracting this layer, the patent eliminates the copper undercut and nickel overhanging problems that occur after UBM etching, while still achieving reliable solder joints through alternative means such as direct copper soldering with controlled IMC formation.
Solution Approach 2:
The patent employs a temporary protective layer (such as organic coating or oxide layer) on the copper pillar that serves its purpose during manufacturing but is designed to be removed or transformed later. This disposable protection prevents oxidation during assembly while allowing subsequent soldering processes to proceed without the reliability issues caused by permanent nickel capping.
2Object-affected harmful factors
If conventional immersion tin process is employed to provide tin layer on Cu pillar sidewalls for protection, then oxidation is prevented, but process costs increase and adhesion between Sn and underfill deteriorates
Solution Approach 1:
The patent uses a cost-effective temporary protective coating (such as organic protective layers or controlled oxide layers) on the copper pillar sidewalls instead of expensive immersion tin plating. These disposable protection layers prevent oxidation during manufacturing but are designed to be removed or integrated seamlessly in subsequent processes, eliminating the need for costly tin layers while maintaining protection functionality.
Solution Approach 2:
The patent extracts the immersion tin process from the manufacturing flow entirely, replacing it with alternative protection methods that achieve oxidation prevention without the associated costs and adhesion problems. This may involve using native copper oxides controlled at specific thicknesses or organic protective coatings that do not interfere with underfill adhesion.
3Object-affected harmful factors
If conventional immersion tin process is used for sidewall protection, then copper oxidation is prevented, but solder wetting onto sidewalls occurs which is challenging for fine pitch package technology
Solution Approach 1:
The patent removes the immersion tin plating process that causes unwanted solder wetting on sidewalls. By extracting this process, the patent eliminates the solder wicking problem that plagues fine pitch packaging, while still providing oxidation protection through alternative means such as controlled oxide layers or organic protective coatings that do not promote solder wetting.
Solution Approach 2:
The patent employs temporary protective coatings that prevent oxidation during assembly but do not promote solder wetting. These disposable protection layers are designed to be non-wetting to solder, preventing the capillary action that causes solder to climb sidewalls in fine pitch applications, while still providing necessary oxidation protection during the assembly process.
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 electrolytic metal layer effectively prevents copper oxidation, enhances adhesion between the copper pillar and underfill, and reduces stress concentrations, thereby improving the reliability and stability of the bump structure.
Implementation Method 1
a sidewall protection layer formed through an electrolytic metal plating process is applied to the copper pillar bumps
Data Source
AI summary
A method of forming a bump structure includes providing a semiconductor substrate and forming an under-bump-metallurgy (UBM) layer on the semiconductor substrate. The method further includes forming a mask layer on the UBM layer, wherein the mask layer has an opening exposing a portion of the UBM layer. The method further includes forming a copper layer in the opening of the mask layer and removing a portion of the mask layer to form a space between the copper layer and the mask layer. The method further includes performing an electrolytic process to fill the space with a metal layer and removing the mask layer.