Pad Structure With Intermetallic Barrier For Galvanic Corrosion

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Solution Overview

Problem

Conventional printed circuit boards face issues with galvanic corrosion when different metals are in contact, leading to erosion of vias during etching, which can result in weakened structures and unreliable electrical connections.

Innovation Solution

A pad structure is developed with an insulating layer, a first metal layer containing an intermetallic compound layer of copper and tin, and a second metal layer with a gold layer, and a mounted structure with a tin-nickel intermetallic compound layer, which suppresses galvanic corrosion by using chemically stable materials that resist etching solutions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If different kinds of metals are in contact with each other in the via, then electrical connection is achieved, but galvanic corrosion occurs causing via erosion

Engineering Contradiction:

Improveelectrical connection reliabilityVSAvoidgalvanic corrosion

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent introduces a barrier metal layer (such as nickel or palladium) as an intermediary between dissimilar metals in the via structure. This intermediate layer prevents direct contact between metals with different electrode potentials, thereby eliminating the galvanic corrosion pathway while maintaining electrical conductivity through the via stack.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The via structure employs a composite material approach by stacking multiple metal layers with different properties - conductive metals for electrical connection, barrier metals for corrosion prevention, and etch-stop layers for structural integrity. This multi-layer composite structure simultaneously achieves electrical functionality and corrosion resistance.

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If etching is used to remove unnecessary via parts, then via shape is refined, but via erosion occurs due to galvanic corrosion

Engineering Contradiction:

Improvevia shape precisionVSAvoidvia strength

Core Design Contradiction:

Manufacturing precisionVSStrength

Solution Approach 1:

The patent applies preliminary protective actions by forming corrosion-resistant barrier layers and etch-stop layers before the etching process. These pre-formed layers protect the via structure from galvanic corrosion that would otherwise occur during etching, allowing aggressive etching conditions to be used for precise via shaping without compromising via strength.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The via structure incorporates cushioning layers (such as etch-stop layers or protective metal layers) that are positioned beforehand to absorb or prevent the harmful effects of etching processes. These layers act as a buffer that protects the underlying via structure from erosion while allowing the etching process to proceed for precise via formation.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Reliability

If multiple metal layers are formed for electrical connection, then conductivity is improved, but galvanic corrosion risk increases

Engineering Contradiction:

Improveelectrical connection reliabilityVSAvoidgalvanic corrosion susceptibility

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

Between each pair of dissimilar metal layers in the via stack, the patent introduces intermediary barrier layers (such as nickel, palladium, or other corrosion-resistant metals). These intermediate layers serve as galvanic isolation barriers that prevent electrochemical reactions between adjacent metals with different electrode potentials, thereby eliminating galvanic corrosion pathways while maintaining the multi-layer conductive structure.

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 effectively prevents undercut formation and maintains structural integrity and electrical reliability by minimizing galvanic corrosion, reducing the risk of voids and defects in the pad and mounted structures.

Implementation Method 1

conventionally, it is known that galvanic corrosion is generated when different kinds of metals are in contact with each other, depending on a combination of the metals

Methodology Applied

Scientific EffectGalvanic corrosion:

Implementation Method 2

a first metal layer formed on one surface of the insulating layer and including an intermetallic compound layer of copper and tin

Methodology Applied

Scientific EffectIntermetallic compound formation:

Implementation Method 3

a second metal layer formed on the first metal layer and including a gold layer

Methodology Applied

Scientific EffectCorrosion resistance:

Data Source

PatentUS9392703B2Pad structure and mounted structure

Publication Date: 2016.07.12 SHINKO ELECTRIC IND CO LTD

AI summary

A pad structure includes an insulating layer; a first metal layer formed on one surface of the insulating layer and including an intermetallic compound layer of copper and tin or a tin layer; and a second metal layer formed on the first metal layer and including a gold layer.