Conductive Pillar Solder Bump Formation via Gas Barrier
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for forming fine solder bumps using the Injection Molded Solder (IMS) method face challenges such as gas outgassing from resist masks, leading to incomplete solder filling, contamination, and increased risk of solder leakage due to high injection pressures, which result in non-uniform and defective solder bumps.
Innovation Solution
The method involves forming conductive layers on the side walls of the resist layer openings to block gas emanation, using metals with solder wettability and higher melting points than the molten solder, which suppress outgassing, allow lower pressure solder injection, and dissolve into the solder for easy resist removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If injection pressure is increased to improve solder filling, then solder filling rate is improved, but solder leakage risk increases
Solution Approach 1:
A release agent layer is introduced as an intermediary between the resist mask and the solder. This release agent has controlled outgassing properties that allow the solder to fill the openings effectively while preventing excessive gas pressure buildup that would cause solder leakage. The release agent mediates the interaction between the resist mask and solder, enabling lower injection pressures to be used.
Solution Approach 2:
The invention changes the chemical and physical parameters of the interface between the resist mask and solder by applying a release agent layer. This layer has specific surface energy and outgassing characteristics that differ from both the resist mask and the solder, allowing optimization of the filling process. The release agent's controlled outgassing rate and surface properties enable solder to wet and fill openings at lower pressures, reducing leakage risk while maintaining high filling rates.
2Manufacturing precision
If injection pressure is increased to improve solder filling, then solder filling rate is improved, but resist material deformation occurs
Solution Approach 1:
The release agent layer serves as a protective intermediary between the resist mask structure and the injected solder. It allows solder to fill the openings effectively while the layer itself absorbs and distributes the pressure, preventing the high forces from deforming the resist material structure.
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 achieves high solder filling rates with reduced leakage risk, enabling the formation of uniform and low-defect solder bumps by maintaining vacuum conditions and preventing electrode surface contamination.
Implementation Method 1
conductive layers which cover at least side walls of the resist layer in the openings is formed before injecting solder to block gas emanating from the resist layer
Implementation Method 2
the solder does not wet and spread to the electrode pads
Implementation Method 3
make it easier to solder injection into the openings at a lower pressure
Implementation Method 4
the conductive layers dissolve into the molten solder in IMS process, it is possible to expose the resist surface
Data Source
AI summary
A method of forming solder bumps includes preparing a substrate having a surface on which a plurality of electrode pads are formed, forming a resist layer on the substrate, the resist layer having a plurality of openings, each of the openings being aligned with a corresponding electrode pad of the plurality of electrode pads, forming a conductive pillar in each of the openings of the resist layer, forming conductive layers to cover at least side walls of the resist layer in the openings to block gas emanating from the resist layer, filling molten solder in each of the openings in which the conductive layers has been formed and removing the resist layer.