Bi-Cu Joining Structure for High-Temperature Semiconductor Bonding
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Solution Overview
Problem
Existing joining materials for semiconductor elements fail to provide adequate heat resistance and stability under high-temperature conditions, leading to potential circuit breakdowns and crack failures due to thermal stress, especially when using GaN or SiC chips with high heat generation.
Innovation Solution
A joining structure and material comprising a first metal phase with Bi as the main component and a second metal phase containing Cu, dispersed in a three-dimensional network structure, forming an intermetallic compound with a Sn-Bi-In-based alloy, which maintains structural integrity at temperatures above 260°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional solder material (Au-20 mass % Sn) is used for joining semiconductor element to insulating substrate, then joining strength is achieved, but heat resistance is insufficient and solder material melts at high temperature causing semiconductor element to incline and potential circuit breakdown
Solution Approach 1:
The patent changes the material parameters of the joining material by using a eutectic alloy composition (Sn-3 mass % Ag-0.5 mass % Cu) with a specific melting point of 217°C, and controls the reflow soldering temperature to be higher than the melting point by 20°C to 40°C (237°C to 257°C). This parameter optimization ensures the joining material achieves adequate heat resistance while maintaining joining reliability.
Solution Approach 2:
The patent employs a composite joining material system consisting of multiple metal elements (Sn, Ag, Cu) forming a eutectic alloy. This composite material combines the advantages of each element: Sn provides low melting point and good wetting, Ag enhances strength and heat resistance, and Cu improves electrical conductivity and reduces oxidation. The synergistic combination achieves both heat resistance and joining stability.
2Speed
If GaN or SiC chips with high heat generation are used, then operational speed and output are improved, but thermal stress from linear expansion coefficient difference causes crack failure in joining part
Solution Approach 1:
The patent optimizes the thermal and mechanical parameters of the joining material by selecting a eutectic alloy composition with appropriate melting point, thermal conductivity, and coefficient of thermal expansion. The Sn-3 mass % Ag-0.5 mass % Cu composition provides balanced properties that reduce thermal stress while maintaining joining strength, enabling the system to withstand high-temperature operation of GaN and SiC chips.
Solution Approach 2:
The composite eutectic alloy joining material combines multiple metal elements with complementary properties. Ag and Cu additions to the Sn base improve the joining material's thermal conductivity and mechanical strength, while the eutectic composition ensures low melting point for easy processing. This composite structure effectively manages thermal stress from GaN and SiC chips during high-speed operation.
3Volume of moving object
If first joining part has small heat flux sectional area, then joining structure is compact, but heat release rate is insufficient for high heat generation semiconductor elements
Solution Approach 1:
The patent optimizes the thermal parameters of the joining material by selecting a eutectic alloy with high thermal conductivity. The Sn-3 mass % Ag-0.5 mass % Cu composition provides adequate thermal conductivity to facilitate heat dissipation from the semiconductor element through the joining part, reducing heat accumulation while maintaining a compact structure.
Solution Approach 2:
The composite eutectic alloy joining material incorporates Ag and Cu elements known for their high thermal conductivity into the Sn matrix. This composite structure enhances the heat flux capability of the joining part, enabling efficient heat transfer from high-power GaN and SiC semiconductor elements while maintaining a compact design with limited volume.
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 joining structure achieves high heat resistance and strength, preventing cracks and maintaining electrical conductivity even under high-temperature conditions, while reducing energy consumption and assembly time.
Implementation Method 1
a second metal phase containing Cu as a main component and containing Sn and In, the first metal phase is dispersed in the second metal phase
Implementation Method 2
forming an intermetallic compound with a Sn-Bi-In-based alloy
Data Source
AI summary
A joining structure including a joining part that joins two objects, in which the joining part includes a first metal phase containing Bi as a main component, the first metal phase having a granular shape with an average size of 0.5 μm to 5 μm, and a second metal phase containing Cu as a main component and containing Sn and In, the first metal phase is dispersed in the second metal phase, and the joining part has a metal composition ratio of Sn: 9.4 mass % to 19.4 mass %, Bi: 26.7 mass % to 36.7 mass %, In: 6.5 mass % to 16.5 mass %, and Cu: a balance.