Au-Sn Alloy Bump Void Control via Sn-Rich Crystal Phase
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Solution Overview
Problem
Au—Sn alloy bumps produced using a paste with 20 mass % Sn and the balance Au and unavoidable impurities often contain large voids, which lead to unreliable jointing due to cracking, necessitating the development of bumps without voids larger than 30% of the bump diameter.
Innovation Solution
The production of Au—Sn alloy bumps involves mixing Au—Sn alloy powder with flux and subjecting it to reflow treatment, where the powder composition contains Sn: 20.5 to 23.5 mass % and a structure with 0.5 to 30 area % Sn-rich primary crystal phase, ensuring no large voids by controlling the mixing and atomization process to prevent Au-rich primary crystal phase growth and enhance flowability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional Au—Sn alloy powder with 20 mass % Sn composition is used for producing Au—Sn alloy bumps, then the bumps can be formed through reflow treatment, but large residual voids are generated in the interior of the bumps
Solution Approach 1:
The invention changes the compositional parameters by specifying Sn content of 20.5 to 23.5 mass % (narrowing the range around the conventional 20 mass %) and controls the microstructural parameters by limiting Sn-rich primary crystal phase to 0.5 to 30 area %. These parameter changes optimize the melting behavior and crystal growth during reflow, preventing large void formation while maintaining jointing reliability
Solution Approach 2:
The invention applies local quality control by specifying the distribution and amount of Sn-rich primary crystal phase within the alloy powder structure. By controlling that 0.5 to 30 area % of Sn-rich primary crystal phase is crystallized in the matrix, the local microstructure is optimized to control void formation during reflow, addressing the void issue without compromising overall bump integrity
2Ease of manufacture
If Au—Sn alloy powder is obtained by gas-atomizing process with 20 mass % Sn composition, then the powder can be used for solder paste, but large residual voids remain in the produced bumps
Solution Approach 1:
The invention modifies the compositional parameters by adjusting Sn content to 20.5 to 23.5 mass % and controls the microstructural parameters by limiting Sn-rich primary crystal phase to 0.5 to 30 area %. These parameter changes optimize the melting behavior and crystal growth during reflow, preventing large void formation while maintaining jointing reliability
3Productivity
If reflow treatment is applied to Au—Sn alloy paste to form bumps, then the bumps can be created on substrate surface, but large voids are trapped in the interior
Solution Approach 1:
The invention applies preliminary action by pre-controlling the microstructure of the Au—Sn alloy powder before the reflow process. By ensuring that 0.5 to 30 area % of Sn-rich primary crystal phase is crystallized in the matrix before reflow, the alloy is prepared in advance to melt and flow properly, enabling void-free bump formation during the subsequent reflow treatment
Solution Approach 2:
The invention optimizes the compositional parameters (Sn: 20.5 to 23.5 mass %) and microstructural parameters (Sn-rich primary crystal phase: 0.5 to 30 area %) to control the melting and solidification behavior during reflow, enabling efficient bump formation without trapped voids
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 method results in Au—Sn alloy bumps with reduced voids, enhancing the reliability of semiconductor device joints and reducing defective product rates, thereby lowering production costs.
Implementation Method 1
subjecting the Au—Sn alloy paste to reflow melting and forming Au—Sn alloy bumps on the surface of the substrate
Implementation Method 2
a structure containing 0.5 to 30 area % of Sn-rich primary crystal phase crystallized in the matrix
Data Source
AI summary
An Au—Sn alloy bump that does not include large voids and a method of producing the same are provided. The Au—Sn alloy bump that does not include large voids comprises a composition containing Sn: 20.5 to 23.5 mass % and the balance Au and unavoidable impurities, and a structure where 0.5 to 30 area % of Sn-rich primary crystal phase is crystallized in the matrix.