Tin Silver Alloy Electrolyte for Uniform Copper Pillar Solder Caps
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Solution Overview
Problem
Existing methods for depositing tin silver alloys onto copper pillars often result in irregular dendrites, leading to defective solder caps and increased waste, as they require sophisticated and accurate deposition methods to achieve uniformity, especially at high current densities.
Innovation Solution
An aqueous composition comprising tin ions, silver ions, unsubstituted or substituted bis(aminophenyl)disulfides, and a specific sulfhydryl-containing compound, such as 2,2'-dithiodianiline, is used for electrolytic deposition, which suppresses dendrite formation and ensures uniformity of solder caps and bumps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional electrolytic deposition methods are used to deposit tin silver alloy onto copper pillars, then the deposition process can be performed, but irregular dendrites form leading to defective solder caps and increased waste
Solution Approach 1:
The patent modifies the chemical parameters of the electrolyte by introducing specific organic complexing agents (carboxylic acids with 2-5 carbon atoms, sulfonic acids with 1-5 carbon atoms, and their salts) to change the deposition characteristics. This alters the electrochemical environment to suppress dendrite formation and achieve uniform solder cap deposition without requiring sophisticated control systems.
Solution Approach 2:
The patent uses organic complexing agents as intermediaries between the tin/silver ions and the copper pillar substrate. These complexing agents form stable complexes with the metal ions, controlling their release and deposition rates during electrolysis, thereby preventing direct uncontrolled deposition that causes dendrites.
2Productivity
If high current densities are applied during electrolytic deposition to increase productivity, then deposition speed increases, but dendrite formation is exacerbated leading to more defects
Solution Approach 1:
The patent changes the electrolyte composition parameters by adding specific organic acids and their salts, which modify the electrical and chemical properties of the solution. This allows the system to handle high current densities without causing dendrite formation, as the complexing agents buffer the electrochemical reactions and maintain uniform current distribution.
Solution Approach 2:
The patent prepares the electrolyte in advance with organic complexing agents that pre-condition the metal ions for controlled deposition. This cushioning effect is built into the electrolyte composition before deposition begins, preventing dendrite formation even when high current densities are subsequently applied to increase productivity.
3Manufacturing precision
If sophisticated and accurate deposition methods are used to achieve uniform solder caps, then manufacturing precision improves, but device complexity and process difficulty increase
Solution Approach 1:
The patent simplifies the deposition process by changing the electrolyte composition to include readily available organic acids and salts. This chemical parameter change inherently provides uniform deposition without requiring sophisticated control systems, complex equipment, or highly skilled operators, thus reducing device complexity while maintaining high manufacturing precision.
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 prevents dendrite formation and achieves high uniformity of tin silver solder caps and bumps, even at high current densities, reducing defective products and improving the quality of solder caps on copper pillars.
Implementation Method 1
an aqueous composition for depositing a tin silver alloy... a method for electrolytically depositing such an alloy onto a substrate
Implementation Method 2
WO 03/046260 A2 relates to an electrolysis bath for electrodepositing silver-tin alloys... an aliphatic complexing agent having a sulfide group and an amino group is used as a complexing agent
Data Source
Figure 1~2
Figure 3
AI summary
The present invention refers to aqueous composition for depositing a tin silver alloy, the composition comprising (a) tin ions, (b) silver ions, (c) at least one first compound independently selected from the group consisting of unsubstituted bis(aminophenyl)disulfides, substituted bis(aminophenyl)disulfides, unsubstituted dipyridyldisulfides, and substituted dipyridyldisulfides, (d) at least one second compound of formula (II) and salts thereof, wherein independently X denotes a C1 to C10 alkyl moiety comprising one or more than one sulfhydryl group, R1 denotes hydrogen, methyl, ethyl, linear C3 to C5 alkyl, branched C3 to C5 alkyl, unsubstituted phenyl, substituted phenyl, unsubstituted benzyl, or substituted benzyl, and R2 denotes methyl, ethyl, linear C3 to C5 alkyl, branched C3 to C5 alkyl, unsubstituted phenyl, substituted phenyl, unsubstituted benzyl, or substituted benzyl.