Al-Si Connection Material for Thermal Cycling and Bond Strength
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Solution Overview
Problem
Next-generation power semiconductor devices require Al connection materials with improved temperature cycle reliability and bonding strength to withstand rapid temperature changes and thermal stress, as conventional materials fail to maintain reliability in rapid temperature cycle tests and can cause bonding failures or chip damage.
Innovation Solution
An Al connection material containing 3.0% to 12.0% Si and 5 to 800 ppm of Sr, Eu, and Na, with specific ratios and distributions of Si phases and Al phases in the L cross-section, enhancing thermal fatigue resistance and bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-purity Al connection material is used, then electrical conductivity and cost are improved, but temperature cycle reliability deteriorates due to thermal stress
Solution Approach 1:
The patent changes the chemical composition parameters of the Al connection material by adding specific amounts of Si (0.01-5.0 mass%), Sr (0.003-0.03 mass%), Eu (0.003-0.03 mass%), and Na (0.003-0.03 mass%). This compositional modification enables the material to withstand thermal stress during temperature cycling while maintaining electrical conductivity, resolving the contradiction between reliability under thermal stress and material purity.
Solution Approach 2:
The patent creates a composite Al-based alloy material combining Al with Si, Sr, Eu, and Na elements. This composite structure provides both the electrical conductivity of Al and the thermal stress resistance through the synergistic effects of the alloying elements, particularly Si for strength and Sr/Eu/Na for controlling intermetallic compound formation and phase distribution.
2Strength
If Si content is increased to improve strength, then temperature cycle reliability is improved, but bonding strength deteriorates due to excessive intermetallic compound formation
Solution Approach 1:
The patent precisely controls the Si content parameter within 0.01-5.0 mass% and combines it with specific amounts of Sr, Eu, and Na. This parameter optimization ensures sufficient Si for thermal fatigue resistance while preventing excessive intermetallic compound formation that would harm bonding strength. The balanced composition achieves both requirements simultaneously.
Solution Approach 2:
The patent uses Sr, Eu, and Na elements to locally control the distribution and morphology of intermetallic compounds formed by Si. These elements modify the local microstructure to prevent harmful large-scale intermetallic formation while maintaining beneficial local reinforcement, thus preserving bonding strength while improving thermal fatigue resistance.
3Reliability
If Al connection material is strengthened by adding elements, then temperature cycle reliability is improved, but ease of manufacture deteriorates due to complex composition control
Solution Approach 1:
The patent defines specific numerical ranges for each alloying element (Si: 0.01-5.0%, Sr: 0.003-0.03%, Eu: 0.003-0.03%, Na: 0.003-0.03%) that can be directly used as manufacturing specifications. These clear parameter ranges simplify the manufacturing process by providing explicit targets for composition control, reducing the complexity of quality management while ensuring temperature cycle reliability.
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 material achieves excellent temperature cycle reliability and stable bonding strength, even under rapid temperature changes, reducing thermal stress and preventing bonding failures.
Implementation Method 1
a solid solution amount of Fe is 0.01 to 0.06%, a precipitation amount of Fe is 7 times or less the Fe solid solution amount
Implementation Method 2
an average value of a ratio between a short side length e and a long side length f (e/f) of a Si phase in an L cross-section
Implementation Method 3
thermal stress, which is caused by a thermal expansion difference between the Al connection material and the semiconductor chip, is repeatedly applied to the 1st bonding part
Implementation Method 4
wedge bonding is a method for applying ultrasonic vibrations and loads to the Al connection material via a jig (tool) made of metal, breaking surface oxide films of the Al connection material and an electrode material to expose new surfaces
Data Source
Figure 1~2
Figure 3
AI summary
To provide an Al connection material satisfying excellent temperature cycle reliability and favorable 1st bonding strength. The Al connection material containing 3.0% by mass or more and 12.0% by mass or less of Si, and containing 5 mass ppm or more and 800 mass ppm or less of one or more of Sr, Eu, and Na in total, in which an average value of a ratio between a short side length e and a long side length f (e/f) of a Si phase in an L cross-section (cross section in a center axis direction including a center axis) of the Al connection material is equal to or larger than 0.25 and equal to or smaller than 0.65.