Semiconductor Electrode Pad with CuAl Alloy Layers
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Solution Overview
Problem
Semiconductor devices experience defects and reliability issues at higher temperatures due to thermal deterioration and halogen-induced corrosion in the junction between electrode pads and bonding wires, particularly with aluminum and copper wire configurations.
Innovation Solution
A semiconductor device configuration featuring an electrode pad with aluminum as a major constituent and copper, coupled with a copper-containing bonding wire, and encapsulated with a halogen-free resin, utilizing multiple layers of copper-aluminum alloys with varying compositions to enhance junction reliability and electrical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gold wires are bonded to aluminum silicon alloy interconnects, then electrical connection is achieved, but peeling occurs at the junction when kept in higher temperature environment of 200 degree C. or higher
Solution Approach 1:
The patent employs a composite material structure consisting of multiple layers including a CuAl2 alloy layer, an Al-Cu-Si alloy layer, and an Al-Si alloy layer. This multi-layer composite structure prevents peeling at the wire-junction interface by creating a gradient of material properties that accommodate thermal expansion differences and reduce stress concentration at interfaces, thereby maintaining junction reliability at elevated temperatures up to 200 degree C. and higher.
Solution Approach 2:
The patent modifies the compositional parameters of the alloy layers, specifically controlling the copper content in the Al-Cu-Si alloy layer to be 0.1-10 wt% and silicon content to be 0.5-5 wt%. By optimizing these parameter ranges, the material achieves both mechanical strength to prevent peeling and thermal stability to resist corrosion at high temperatures, thus resolving the contradiction between reliability and operating temperature.
2Strength
If copper is added to aluminum electrode pad at high ratio to increase hardness, then compressive bonding is improved, but halogen-induced corrosion increases at higher temperatures
Solution Approach 1:
The patent optimizes the copper content parameter in the Al-Cu-Si alloy layer to be within 0.1-10 wt%, which provides sufficient hardness (70-100 Vickers hardness) to prevent peeling during compressive bonding, while simultaneously limiting copper-induced corrosion susceptibility. This parameter optimization resolves the contradiction between achieving adequate strength and minimizing halogen-induced corrosion at elevated temperatures.
Solution Approach 2:
The patent creates a multi-layer structure where each layer has different local composition and properties: the CuAl2 layer provides strong adhesion, the Al-Cu-Si layer provides optimized hardness and corrosion resistance, and the Al-Si layer provides thermal stability. This local quality differentiation allows the electrode pad to simultaneously achieve high strength and resistance to halogen-induced corrosion in different regions.
3Object-affected harmful factors
If brominated epoxy resin is used as fire retardant agent in encapsulating resin, then fire resistance is improved, but free bromine compounds are generated due to thermal decomposition
Solution Approach 1:
The patent replaces the brominated epoxy resin with an alternative encapsulating resin composition that does not contain bromine. This substitution eliminates the generation of free bromine compounds through thermal decomposition, thereby preventing corrosion of the Al-Cu-Si alloy layers while still providing the necessary fire retardant properties through alternative mechanisms, thus resolving the contradiction between fire resistance and harmful emissions.
Data Source
AI summary
A semiconductor device includes an electrode pad provided on a semiconductor chip, the electrode pad includes aluminum (Al) of between 50% wt. and 99.9% wt. and further includes copper (Cu), a coupling ball that primarily includes Cu, the coupling ball being coupled to the electrode pad so that a CuAl2 layer, a CuAl layer, a layer including one of Cu9Al4 and Cu3Al2, and the coupling ball are vertically stacked in this order on the electrode pad, and an encapsulating resin that includes a halogen of less than or equal to 1000 ppm, the encapsulating resin covering at least the electrode pad and a junction between the electrode pad and the coupling ball.