Tin-Silver Plating Composition for Uniform Solder Bumps
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Solution Overview
Problem
The challenge is to develop a tin-silver plating solution that minimizes whisker generation and achieves uniform silver composition during high-speed plating, addressing issues with current density limitations and silver ion control in tin-silver solder bump manufacturing for flip chip mounting.
Innovation Solution
A tin-silver plating solution containing tin ions, silver ions, and an organic additive comprising a silver complexing agent, a tin carrier, and a crystal grain refiner, with specific chemical formulations and ratios, is used to stabilize the plating process and prevent silver precipitation, allowing for high-speed plating with controlled silver composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high current density is used during plating to increase plating speed, then productivity is improved, but manufacturing precision deteriorates due to poor plating control and void formation
Solution Approach 1:
The patent modifies the chemical composition parameters of the plating solution by introducing specific organic additives (complexing agents and crystal grain refiners) to enable high current density plating while maintaining surface quality. The complexing agent concentration is controlled at 0.01-10 g/L and crystal grain refiner at 0.01-5 g/L to achieve optimal plating characteristics at high current densities
Solution Approach 2:
The patent introduces organic additives as intermediary substances that mediate between the high current density electrical field and the metal ion deposition process. The complexing agents and crystal grain refiners act as intermediaries to control nucleation and growth, preventing direct harmful effects of high current density while maintaining high plating speed
2Manufacturing precision
If silver ion concentration is increased to achieve uniform silver composition, then manufacturing precision is improved, but reliability deteriorates due to precipitation on UBM layer and tin anode
Solution Approach 1:
The patent introduces a complexing agent as an intermediary substance that binds to silver ions in solution, preventing their direct precipitation on the UBM layer and tin anode. This intermediary complex keeps silver ions in solution at higher concentrations while controlling their deposition behavior to achieve uniform distribution without reliability issues
Solution Approach 2:
The patent changes the chemical state of silver from free ions to complexed ions by adding organic complexing agents. This parameter change in the chemical form of silver allows for higher effective silver content while preventing precipitation, thus achieving uniform composition without compromising reliability
3Ease of operation
If conventional tin-lead solder bumps are used to achieve good soldering characteristics, then ease of operation is improved, but reliability deteriorates due to whisker generation and RoHS compliance issues
Solution Approach 1:
The patent changes the alloy composition parameters by eliminating lead and using tin-silver alloys with controlled silver content (0.1-5 wt%). Combined with organic additives, this composition change maintains solderability while eliminating whisker generation and meeting RoHS requirements
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 solution effectively reduces whisker generation, ensures uniform silver composition, and enhances the surface roughness and solderability of tin-silver solder bumps, improving their reliability and processability, even at high current densities.
Implementation Method 1
the organic additive includes a silver (Ag) complexing agent represented by the following Chemical Formula 1
Implementation Method 2
a tin carrier represented by the following Chemical Formula 2
Implementation Method 3
a method of forming a tin-silver solder bump, including: exposing an under-bump-metallurgy structure to a plating bath containing a tin-silver plating solution
Implementation Method 4
a crystal grain refiner represented by the following Chemical Formula 3
Implementation Method 5
diminishing whisker generation in high-speed plating
Implementation Method 6
excessive hydrogen gas is generated from the plating electrode
Data Source
AI summary
As a tin-silver plating solution that contains a source of tin ions; a source of silver ions (Ag+); and an organic additive including a silver (Ag) complexing agent, a tin carrier, and a crystal grain refiner is provided, in the case of performing high-speed plating using the plating solution, the generation of whiskers is diminished, the composition of silver ions (Ag+) in the tin-silver plating solution is uniformly maintained, and thus a uniform silver composition in the formed tin-silver solder bumps can be achieved.