Ionic Metal Activation with Sulfur Compounds for Electroless Plating

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Solution Overview

Problem

Conventional methods for electroless metal deposition on printed circuit boards and IC substrates face challenges due to the sensitivity of palladium/tin colloids to air and high costs, and ionic metal activation requires excessive reducing agents, leading to economic and ecological inefficiencies.

Innovation Solution

A process involving ionic metal activation using a solution comprising metal ions like ruthenium, rhodium, or palladium, combined with thiols, thioethers, or sulphur-containing heterocycles, and boron-based reducing agents to reduce metal ions adsorbed on substrates, reducing the excess of reducing agents needed and minimizing decomposition.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If palladium/tin colloid is used for activation, then electroless metal deposition can be initiated, but the colloid is sensitive to air and has high cost

Engineering Contradiction:

Improveactivation effectivenessVSAvoidair sensitivity

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent replaces expensive and air-sensitive palladium/tin colloid with a more economical activation system using metal ions (such as Pd2+, Ru3+, Rh3+) combined with sulfur-containing compounds. The metal ions are adsorbed onto the substrate and then reduced in situ by sulfur compounds to form metallic particles that initiate electroless deposition. This approach uses cheaper, more stable materials while maintaining activation effectiveness.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Reliability

If ionic metal activation is used with reducing agents, then metal ions can be reduced on the surface, but excessive reducing agents are required leading to economic and ecological inefficiencies

Engineering Contradiction:

Improveactivation efficiencyVSAvoidreducing agent excess

Core Design Contradiction:

ReliabilityVSLoss of substance

Solution Approach 1:

The patent employs sulfur-containing compounds (thiols, thioethers, sulphur-containing heterocycles) that serve dual functions: they act as adsorbents for metal ions and simultaneously serve as reducing agents to convert metal ions to metallic particles on the substrate surface. This self-service mechanism eliminates the need for separate reducing agents and their associated excess usage problems, improving both economic and ecological efficiency.

Inventive Principle:

Principle #25Self-service

3Stability of the object's composition

If tin(II) ions are used to stabilize palladium colloid, then colloidal structure is maintained, but tin(II) oxidizes to tin(IV) causing colloid instability

Engineering Contradiction:

Improvecolloidal structure stabilityVSAvoidcolloid stability

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The patent replaces the unstable palladium/tin colloid system with a fresh activation system where metal ions are adsorbed and reduced in situ on each substrate. This eliminates the need for pre-stabilized colloids that suffer from oxidation issues, using instead a on-demand activation approach with sulfur-containing compounds that provide both adsorption and reduction functions.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 process achieves efficient metal deposition with improved economic and ecological outcomes by reducing the excess of reducing agents required, maintaining process results such as coverage, conductivity, and adhesion, while lowering the decomposition rate of reducing agents.

Implementation Method 1

Methodology Applied

Scientific EffectAdsorption: Adsorption

Implementation Method 2

treating the surface of said substrate obtained from step (b) with a treatment solution comprising i) at least one additive selected from the group consisting of thiols, thioethers, disulphides and sulphur containing heterocycles, and ii) at least one reducing agent suitable to reduce the metal ions adsorbed on the surface of said substrate

Methodology Applied

Scientific EffectReduction: Reduction

Implementation Method 3

treating the surface obtained from step (c) of said substrate with a metallizing solution comprising a solvent and at least one source of metal ions to be deposited thereon such that a metal or metal alloy is deposited thereon

Methodology Applied

Scientific EffectElectroless plating: Deposition (physical)

Data Source

PatentUS10975474B2Process for depositing a metal or metal alloy on a surface of a substrate including its activation

Publication Date: 2021.04.13 ATOTECH DEUT GMBH & CO KG

AI summary

A process for depositing metal or metal alloy on a substrate including treating the substrate surface with an activation solution comprising a source of metal ions so the metal ions are adsorbed on the substrate surface, treating the obtained substrate surface with a treatment solution containing an additive selected from thiols, thioethers, disulphides and sulphur containing heterocycles, and a reducing agent suitable to reduce the metal ions adsorbed on the substrate surface selected from boron based reducing agents, hypophosphite ions, hydrazine and hydrazine derivatives, ascorbic acid, iso-ascorbic acid, sources of formaldehyde, glyoxylic acid, sources of glyoxylic acid, glycolic acid, formic acid, sugars, and salts of aforementioned acids; and subsequently treating the substrate surface with a metallizing solution comprising a source of metal ions to be deposited such that a metal or metal alloy is deposited thereon.