Multilayer Electrode Structure for Lead-Free Solder Bonding
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Solution Overview
Problem
The use of lead-free solder bumps in semiconductor devices results in lower bonding strength and increased stress at the junction interface, leading to potential disconnection and reduced mounting reliability due to the formation of brittle ternary compound layers, especially when electroless plating is used.
Innovation Solution
A circuit board and semiconductor device design featuring a multilayer electrode structure with a copper layer, a nickel layer, and a tin-nickel alloy layer, where a tin layer is applied on top to form a barrier layer composed of a tin-nickel compound, preventing copper diffusion and enhancing bonding strength by placing the tin-nickel alloy layer between the nickel and ternary compound layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead-free solder bumps are used, then environmental compliance is improved, but bonding strength deteriorates
Solution Approach 1:
The patent applies composite materials by creating a multilayer electrode structure consisting of copper layer, nickel layer, and tin-nickel alloy layer. This composite structure is designed to provide both environmental compliance through lead-free solder compatibility and sufficient bonding strength through the synergistic properties of different metal layers, particularly the tin-nickel alloy layer that prevents brittle ternary compound formation.
Solution Approach 2:
The tin-nickel alloy layer serves as an intermediary between the nickel layer and the lead-free solder bump. This intermediate layer prevents direct contact between nickel and solder, thereby preventing the formation of brittle ternary compounds (Ni-Sn-Cu) that would otherwise reduce bonding strength. The intermediary layer maintains strong bonding while enabling lead-free solder usage.
2Productivity
If electroless plating is used for nickel layer formation, then manufacturing efficiency is improved, but junction interface stress increases
Solution Approach 1:
The patent changes the chemical composition parameters of the electrode layers, specifically introducing a tin-nickel alloy layer with controlled ratios of tin and nickel. This parameter change in the alloy composition prevents excessive stress formation at the junction interface while maintaining the manufacturing efficiency benefits of electroless plating for the nickel layer.
Solution Approach 2:
The electroless plated nickel layer is combined with the tin-nickel alloy layer to create a composite electrode structure. This composite approach maintains the high manufacturing efficiency of electroless plating while the tin-nickel alloy component reduces junction interface stress by preventing brittle compound formation and providing a more compliant interface.
3Stability of the object's composition
If copper diffusion prevention is enhanced, then electrode integrity is improved, but layer structure complexity increases
Solution Approach 1:
The nickel layer and tin-nickel alloy layer serve as intermediaries that prevent copper diffusion from the copper layer into the solder bump. Rather than using a single complex diffusion barrier, the patent uses these intermediate layers to achieve copper prevention while maintaining a manageable three-layer structure that balances integrity with complexity.
Solution Approach 2:
The electrode structure is segmented into distinct functional layers: copper layer for electrical conductivity, nickel layer for oxidation prevention and partial diffusion barrier, and tin-nickel alloy layer for solder bonding and additional diffusion prevention. This segmentation allows each layer to perform its specific function efficiently while maintaining overall electrode integrity.
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
This configuration ensures sufficient bonding strength between the lead-free solder bumps and the electrode, comparable to lead-containing solder embodiments, while preventing nickel and copper diffusion, thus improving mounting reliability and thermal fatigue resistance.
Implementation Method 1
a tin layer is applied on top to form a barrier layer composed of a tin-nickel compound, preventing copper diffusion
Implementation Method 2
preventing nickel and copper diffusion
Data Source
AI summary
There is provided a circuit board to which a solder ball composed of a lead (Pb)-free solder is to be connected, a semiconductor device including an electrode and a solder ball composed of a lead (Pb)-free solder disposed on the electrode, and a method of manufacturing the semiconductor device, in which mounting reliability can be improved by enhancing the bonding strength (adhesion strength) between the solder ball composed of a lead (Pb)-free solder and the electrode.