Semiconductor Solder Joints Using Segmented Sn-Ag and Sn-Cu Layers
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Solution Overview
Problem
The existing semiconductor devices using Pb-free solders face issues with thermal stress relaxation and fatigue resistance due to the use of Sn—Ag and Sn—Cu alloys, leading to potential cracks and delamination, especially with low-k films, and the high cost and difficulty in controlling Ag plating for solder bump formation.
Innovation Solution
A method for manufacturing semiconductor devices using a Sn alloy with controlled compositions of Ag and Cu for the solder connecting part, where the preliminary solder layer contains Ag and the solder bump contains Cu, improving both thermal stress relaxation and fatigue resistance, while reducing manufacturing costs through stacked plating techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a Sn—Ag alloy is used for the solder bump, then the connection strength is improved, but the creeping property decreases and thermal stress relaxation is insufficient
Solution Approach 1:
The invention applies different alloying strategies to different components of the solder connection system. The solder bump uses Sn—Ag alloy for high strength, while the preliminary solder layer uses Sn—Cu alloy for good creepability and thermal stress relaxation. This local differentiation allows each component to optimize its function, resolving the contradiction between connection strength and thermal stress relaxation.
Solution Approach 2:
The invention creates a composite solder connection system by combining Sn—Ag alloy solder bumps with Sn—Cu alloy preliminary solder layers. This composite approach leverages the complementary properties of both alloys: Ag provides strength enhancement while Cu provides creep resistance and thermal stress relaxation, together achieving both high connection strength and reliable thermal stress management.
2Reliability
If a Sn—Cu alloy is used for the solder bump, then the creeping property and thermal stress relaxation are improved, but the solder embrittles and fatigue resistance decreases
Solution Approach 1:
The invention assigns different material functions to different components: the preliminary solder layer (fixed position) uses Sn—Cu for optimal creepability and thermal stress relaxation, while the solder bump (subject to thermal cycling) uses Sn—Ag for superior fatigue resistance. This spatial differentiation of material properties resolves the contradiction between thermal stress relaxation and fatigue resistance.
3Manufacturing precision
If electrolytic plating of alloy is used for solder bump formation, then the solder bump quality is improved, but the manufacturing cost increases and solution lifetime decreases
Solution Approach 1:
The invention segments the solder formation process into two independent plating steps: first forming a Cu layer, then forming an Ag layer. This segmentation allows each plating step to use optimized parameters and materials, improving overall solder bump quality while enabling better cost control and extended solution lifetime compared to single-step alloy plating.
Solution Approach 2:
The invention performs preliminary Cu plating before Ag plating. This preliminary action creates a foundation layer that prevents direct contact between the Ag plating solution and the substrate, extending the Ag plating solution lifetime. Additionally, the Cu layer serves as a diffusion barrier, ensuring high-quality solder bumps with controlled composition.
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 method effectively suppresses cracks and delamination in semiconductor devices, enhances fatigue resistance, and reduces manufacturing costs by optimizing the composition and formation of the solder connecting part, ensuring reliable performance under thermal cycles.
Implementation Method 1
melting the preliminary solder layer and the solder bump by heating to a temperature equal to or higher than melting points thereof
Data Source
AI summary
In one embodiment, a preliminary solder layer made of a Sn alloy is formed on a connecting pad of a wiring substrate. A solder bump made of a Sn alloy is formed on an electrode pad of a semiconductor chip. After contacting the preliminary solder layer and the solder bump, the preliminary solder layer and the solder bump are melted by heating to a temperature of their melting points or higher to form a solder connecting part made of a Sn alloy containing Ag and Cu. Only the preliminary solder layer of the preliminary solder layer and the solder bump is composed of a Sn alloy containing Ag.