Homogeneous Bi Distribution in Sn-Bi Solder Plating for Semiconductor Bumps
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Solution Overview
Problem
In high-density semiconductor packaging, the concentration gradient of Bi in Sn-based solder alloys on Cu core balls leads to uneven melting, causing positional shifts and potential short circuits due to volume expansion differences between the inner and outer circumference sides during the reflow process.
Innovation Solution
A core material with a Bi concentration ratio in the solder plating layer set between 91.4% to 106.7% ensures homogeneous Bi distribution, preventing early melting on the inner circumference side and minimizing volume expansion differences, thereby maintaining the core's position and preventing short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a plating treatment is performed with a concentration gradient where Bi content decreases towards the inner side and increases towards the outer side, then the manufacturing complexity is reduced, but uneven melting occurs during reflow causing positional shifts and potential short circuits
Solution Approach 1:
The patent applies homogeneity by maintaining uniform Bi concentration throughout the solder plating layer. The specification requires Bi content to be 3-10 mass% across the entire layer, eliminating the concentration gradient found in conventional approaches. This uniform distribution ensures simultaneous melting during reflow, preventing the inner circumference side from melting earlier than the outer side, thereby avoiding positional shifts and short circuits while maintaining manufacturing feasibility
2Ease of manufacture
If a solder plating layer with Bi concentration gradient is used to simplify manufacturing, then production ease is improved, but the reliability decreases due to early melting and positional shifts
Solution Approach 1:
The patent eliminates the Bi concentration gradient to achieve uniform composition throughout the solder plating layer. By maintaining consistent Bi content (3-10 mass%) across the entire layer, the melting behavior becomes uniform during reflow processing. This prevents the reliability issue where the inner circumference side melts earlier than the outer side, which would cause the core material to shift position and potentially create short circuits between electrodes
3Ease of manufacture
If the Bi content in the solder plating layer is increased towards the outer side to facilitate manufacturing, then production simplicity is improved, but melting uniformity deteriorates causing adhesive defects
Solution Approach 1:
The patent applies homogeneity by maintaining uniform Bi concentration (3-10 mass%) throughout the solder plating layer, preventing the composition instability caused by concentration gradients. This uniform composition ensures consistent melting behavior during reflow, eliminating the adhesive defects that occur when the outer side melts at different times than the inner side, while keeping the plating process simple and manufacturable
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 homogeneous Bi distribution in the solder plating layer ensures uniform melting and reduces the risk of positional shifts, ensuring high-quality semiconductor packages without adhesive defects or short circuits.
Implementation Method 1
an electric solder plating layer of an (Sn-Bi)-based solder alloy made of Sn and Bi on a surface of the core, the electric solder plating layer being subjected to electric solder plating
Implementation Method 2
forming the bump electrode by heating the mounted core material
Implementation Method 3
when the core material in which the Sn-based solder alloy made of Sn and Bi is plated and coated on the surface of the Cu ball, is mounted on each of the electrodes of the semiconductor chip, and the reflow process is performed thereon
Data Source
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AI summary
[Problem] [Means for solving the Problem] A core material includes a core 12 and a solder plating layer 16 of an (Sn-Bi)-based solder alloy made of Sn and Bi covered on a surface of the core. Bi in the solder plating layer 16 is distributed in the solder plating layer at a concentration ratio in a predetermined range of, for example, 91.7% to 106.7%. Bi in the solder plating layer is homogeneous, and thus, a Bi concentration ratio is in a predetermined range over the entire range including an inner circumference side and an outer circumference side in the solder plating layer. Therefore, any situation does not occur in which the inner circumference side is earlier melted than the outer circumference side and a volume expansion difference occurs between the inner circumference side and the outer circumference side, and thus, the core material is flicked off. Since the whole of the solder plating layer is almost homogeneously melted, positional shift of the core material due to a shift in the melting timing does not occur, and thus, there is no concern of a short circuit between the electrodes or the like due to the positional shift or the like.