Au-Sn Solder Ball Junction Structure for Thin Reliable Joints
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Solution Overview
Problem
Existing joint structures using AuSn alloy solder pastes or sheet-shaped brazing materials face issues with partially unfused or foreign substance-inclusion joinings, difficulty in reducing joint thickness, and high Au usage, leading to impaired electrical and thermal conductivity and hermeticity.
Innovation Solution
A joint structure utilizing Au—Sn-based alloy solder balls with specific compositions and manufacturing methods to achieve a uniform eutectic alloy, preventing shrinkage cavities and allowing for precise control of joint thickness between 3 μm and 50 μm, thereby enhancing thermal conductivity and joint quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If AuSn alloy particles are dispersed in flux and used as solder paste, then the joining process can be performed, but partially unfused joining or foreign substance-inclusion joining occurs, impairing quality
Solution Approach 1:
The invention extracts and removes the flux component from the joining material, using only the AuSn alloy particles without flux dispersion. This eliminates the source of foreign substance inclusion while maintaining the joining capability through direct particle bonding.
Solution Approach 2:
The invention uses a consumable AuSn alloy sheet that is melted and consumed during the joining process, replacing the reusable solder paste with flux. The sheet material is entirely transformed into the joint, eliminating residual flux-related defects.
2Ease of manufacture
If solder paste is supplied to joining site by printing or discharging, then the joining can be performed, but the thickness of joint portion cannot be reduced
Solution Approach 1:
The invention changes the physical state and form of the joining material from a paste with flux to a solid sheet material with controlled thickness. By controlling the sheet thickness before melting, the final joint thickness is precisely controlled, enabling reduction to 3 μm or more and 50 μm or less.
3Ease of manufacture
If sheet-shaped brazing material is used, then the joining can be performed, but the thickness cannot be reduced because the material is hard and brittle
Solution Approach 1:
The invention changes the material composition parameters by using a AuSn-based alloy with specific Sn content (19-25 mass%) that provides eutectic or near-eutectic composition. This composition change improves ductility and processability while enabling thin joint formation, overcoming the brittleness issue of conventional sheet materials.
4Strength
If AuSn alloy particles are bonded together during reflow, then joining occurs, but foreign substances such as flux are included in the joining
Solution Approach 1:
The invention extracts and removes the flux component from the joining system entirely, using only pure AuSn alloy sheet material. This eliminates the source of foreign substance inclusion while maintaining strong joints through direct metallurgical bonding of the alloy particles.
5Ease of manufacture
If solder paste or brazing material is used, then joining can be performed, but the amount of Au used is high
Solution Approach 1:
The invention changes the alloy composition parameters by optimizing the Sn content to 19-25 mass%, creating a eutectic or near-eutectic composition. This allows for reduced Au content while maintaining joining performance, and the thin joint thickness (3-50 μm) further reduces the total quantity of Au required.
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 solution achieves high thermal conductivity and improved joint quality by forming a uniform eutectic alloy with Au—Sn-based alloy solder balls, reducing Au usage, and preventing appearance defects due to shrinkage cavities, while maintaining reliable electrical and thermal connectivity.
Implementation Method 1
forming a uniform eutectic alloy with Au—Sn-based alloy solder balls
Implementation Method 2
a thickness of the joint portion is 3 μm or more and 50 μm or less
Data Source
AI summary
Provided is a joint structure. The joint structure includes a first structure, and a second structure joined to the first structure via a joint portion formed of a Au—Sn-based alloy, wherein a thickness of the joint portion is 3 μm or more and 50 μm or less.