Tin Alloy Electroplating Solution for Flip Chip Solder Bumps

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Solution Overview

Problem

Conventional flip-chip packaging processes face challenges such as defectiveness, yield issues, height variations, and the formation of empty spaces and cracks in intermetallic compound layers during the formation of solder bumps, which affect the quality and reliability of electronic devices.

Innovation Solution

A tin-based electroplating solution containing tin methanesulfonate, methanesulfonic acid, a fluorinated surfactant, and optional silver methanesulfonate, along with aromatic polyoxyalkylene ether and water, is used to form solder bumps on a metal-based under bump metallurgy layer, enhancing current efficiency, preventing cracks and empty spaces, and ensuring high flatness and reduced height variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional electroplating solutions are used to form solder bumps, then the plating process can be completed, but height variations and defects occur in the formed bumps

Engineering Contradiction:

Improvebump height uniformityVSAvoidbump quality

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent modifies the electroplating solution composition by incorporating specific surfactants and adjusting chemical parameters to achieve uniform bump formation. The solution contains tin salts, surfactants, and other additives in controlled concentrations to optimize plating uniformity and eliminate defects.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Surfactants are introduced as intermediary substances in the electroplating solution to mediate between the electroplating process and the substrate surface. These surfactants improve wetting and distribution of the plating material, ensuring uniform bump formation without height variations.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If conventional electroplating solutions are used, then plating can proceed, but cracks and empty spaces form in the intermetallic compound layers

Engineering Contradiction:

Improveplating process continuityVSAvoidintermetallic compound layer integrity

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent uses surfactants as intermediary agents in the electroplating solution to prevent crack formation and empty space development in intermetallic compound layers. These surfactants ensure uniform material distribution and adhesion during plating, maintaining layer integrity while preserving process continuity.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The electroplating solution composition is optimized with specific concentrations of surfactants and chemical additives to control the plating process parameters. This prevents defects such as cracks and voids in the intermetallic compound layers while maintaining efficient plating production.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If high-speed plating is implemented to increase productivity, then output improves, but manufacturing precision deteriorates

Engineering Contradiction:

Improveplating speedVSAvoidbump flatness and height consistency

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent employs surfactants as intermediary substances that enable high-speed plating while maintaining precision. These surfactants ensure uniform material distribution and wetting even at elevated plating speeds, preventing defects and maintaining bump flatness and height consistency throughout the high-productivity process.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 improves the quality and reliability of solder bumps by enhancing current efficiency, preventing cracks and empty spaces, and achieving high flatness and reduced height variations, making it suitable for high-speed plating applications.

Implementation Method 1

0.01 to 100 mg/L of a fluorinated surfactant

Methodology Applied

Scientific EffectSurface tension reduction: Surfactant

Implementation Method 2

improving current efficiency

Methodology Applied

Scientific EffectWetting: Wetting

Implementation Method 3

tin-based electroplating solution that is used to form tin-based solder bumps on a metal-based UBM layer by electroplating

Methodology Applied

Scientific EffectElectroplating: Electroplating

Implementation Method 4

form solder bumps... by electroplating

Methodology Applied

Scientific EffectElectrochemical reduction: Electrolysis

Implementation Method 5

0.5 to 60 g/L of an aromatic polyoxyalkylene ether

Methodology Applied

Scientific EffectGrain refinement:

Data Source

PatentUS9871010B2Tin alloy electroplating solution for solder bumps including perfluoroalkyl surfactant

Publication Date: 2018.01.16 APCT

AI summary

Disclosed is a tin-based electroplating solution for forming solder bumps of a flip chip package. The tin-based electroplating solution includes tin methanesulfonate, silver methanesulfonate, methanesulfonic acid, a fluorinated surfactant, an aromatic polyoxyalkylene ether, and water. Also disclosed is a method for forming solder bumps by using the electroplating solution. The method includes (1) electroplating a silicon wafer having a protective layer through which an electrode pad is exposed and an under bump metallurgy (UBM) layer with a copper or copper/nickel plating solution to form copper or copper/nickel pillars on the under bump metallurgy layer and (2) electroplating the pillars with the tin-based electroplating solution to form solder bumps.