Lead-Free Solder Bump Ag Content Optimization
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Solution Overview
Problem
Lead-free solder materials with high Ag content face issues such as increased melting point, stress reliability problems, and crack formation due to thermal damage, especially in large die sizes and Cu post technology, which affects the performance and reliability of semiconductor devices.
Innovation Solution
A lead-free solder with controlled Ag content between 1.2 wt% and 1.6 wt% is used, adjusting the reflow temperature between 240° C and 280° C to optimize bump hardness and reduce crack formation, while forming intermetallic compounds and voids, thereby enhancing the reliability of semiconductor devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If high Ag content lead-free solder is used, then melting point increases, but thermal damage and crack formation occur
Solution Approach 1:
The patent optimizes the Ag content parameter within a specific range (2.0-4.5 weight percent) and controls reflow temperature (240-260°C) to achieve the desired balance between melting point and crack resistance, rather than using high Ag content which causes thermal damage
2Temperature
If high Ag content lead-free solder is used, then melting point increases, but stress reliability problems occur
Solution Approach 1:
The patent controls Ag content within 2.0-4.5 weight percent and reflow temperature between 240-260°C to optimize the solder's mechanical properties, achieving adequate stress reliability while maintaining appropriate melting characteristics for the semiconductor device
3Reliability
If Ag content is controlled between 2.0-4.5 wt%, then crack resistance improves, but melting point is lower than high Ag content
Solution Approach 1:
The patent selects Ag content in the range of 2.0-4.5 weight percent and reflow temperature of 240-260°C to achieve crack resistance while maintaining an appropriate melting point for the specific application, balancing reliability and thermal characteristics
4Ease of manufacture
If reflow temperature is increased, then soldering effectiveness improves, but uncompleted ball-shape formation and voids occur
Solution Approach 1:
The patent optimizes reflow temperature within 240-260°C to achieve complete ball-shape formation and minimize voids while ensuring adequate soldering effectiveness, rather than using higher temperatures that cause manufacturing defects
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 controlled Ag content in the lead-free solder improves crack resistance and thermal stress management, ensuring better performance and reliability of semiconductor devices by adjusting the reflow temperature to prevent uncompleted ball-shape formation and voids, thus addressing the reliability issues associated with high Ag content.
Implementation Method 1
The bumps themselves, based on the material used, are classified as solder bumps... The binary Sn—Ag alloy is used as the lead-free solder with Ag between 2.0 ̃4.5 weight percent, which melts at a temperature between 240 ̃260° C.
Implementation Method 2
A solder alloy is still necessary for capping the bump structure and jointing electronic components... The controlled Ag content in the lead-free solder improves crack resistance and thermal stress management
Data Source
AI summary
A semiconductor device includes a semiconductor substrate, a pad region on the semiconductor substrate, a passivation layer over the semiconductor substrate and at least a portion of the pad region, and a bump structure overlying the pad region. The passivation layer has an opening defined therein to expose at least another portion of the pad region. The bump structure is electrically connected to the pad region via the opening. The bump structure includes a copper layer and a SnAg layer overlying the copper layer. The SnAg layer has a melting temperature higher than the eutectic temperature of Sn and Ag.