Solder Bump Metal Cap Layer for Short Prevention
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Solution Overview
Problem
The semiconductor industry faces challenges in achieving high-quality and reliable lead-free solder bumps for finer pitches and larger interconnect densities, with a high risk of shorts occurring during fabrication and flip-chip assembly.
Innovation Solution
A bump formation process involving the use of a metal cap layer with a higher melting point than the solder material, which is formed over the solder bump to act as a spring and prevent deformation, maintaining uniform stand-off height and reducing shorting and bridging issues, while using lead-free solder materials like SnAg and SnCu.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If lead-free solder bumps are used for finer pitches and larger interconnect densities, then environmental safety and worker safety are improved, but the risk of shorts between solder bumps during fabrication and assembly increases
Solution Approach 1:
A metal cap layer (such as nickel, palladium, or gold) is deposited over the lead-free solder bump to serve as an intermediary protective layer. This cap layer prevents direct contact between adjacent solder bumps, eliminating the shorting risk while maintaining the environmental and safety benefits of lead-free soldering.
Solution Approach 2:
The invention changes the physical and chemical parameters of the solder bump structure by adding a metal cap layer with different melting point and conductivity properties. This parameter change (adding a protective overlay) resolves the shorting issue without compromising the lead-free advantage.
2Reliability
If solder bumps are used for flip-chip bonding, then electrical connection between chip and substrate is achieved, but deformation of solder bumps during assembly may occur
Solution Approach 1:
The metal cap layer acts as a protective intermediary shell over the solder bump, maintaining its shape during assembly processes. This cap layer prevents deformation while allowing the solder bump to perform its electrical connection function.
Solution Approach 2:
The metal cap layer is applied beforehand to the solder bump to provide mechanical protection and shape maintenance during subsequent assembly operations, preventing deformation before it can occur.
3Productivity
If interconnect density is increased, then circuit performance is improved, but the risk of shorts between adjacent solder bumps increases
Solution Approach 1:
The metal cap layer serves as a protective intermediary that enables higher interconnect density by preventing shorts between closely spaced solder bumps, thus allowing increased circuit performance without compromising 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
The process enhances the reliability and quality of lead-free solder bumps by maintaining uniform stand-off height and reducing shorting and bridging problems, improving the overall performance and density of semiconductor devices.
Implementation Method 1
a metal cap layer with a higher melting point than the solder material, which is formed over the solder bump to act as a spring and prevent deformation
Implementation Method 2
A thermal reflow of the solder material layer is performed
Data Source
AI summary
A semiconductor device includes a solder bump overlying and electrically connected to a pad region, and a metal cap layer formed on at least a portion of the solder bump. The metal cap layer has a melting temperature greater than the melting temperature of the solder bump.