Mg-Gradient Copper Alloy Plate for Reliable Sn Plating

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Solution Overview

Problem

Copper alloy containing Mg faces challenges in balancing mechanical strength and electrical conductivity, with solder wettability and electrical connection reliability deteriorating after Sn plating and heating treatment due to Mg oxidation and diffusion.

Innovation Solution

A copper alloy plate with a controlled Mg concentration gradient in the surface layer, where the surface Mg concentration is 30% or less of the bulk concentration, preventing oxidation and diffusion into the plating film, and a plating film-attached copper alloy plate with a Mg concentration in the plating film of 10% or less, formed using electrolytic plating with specific current density and reflow treatment to enhance adhesiveness and solder wettability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If Mg is added to copper alloy to improve mechanical strength and electrical conductivity, then strength and conductivity are improved, but solder wettability and electrical connection reliability deteriorate due to Mg oxidation and diffusion into plating film

Engineering Contradiction:

Improvemechanical strengthVSAvoidelectrical connection reliability

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent applies local quality by creating a non-uniform Mg concentration distribution within the copper alloy plate. The surface layer contains suppressed Mg concentration (10-30 mass ppm) to prevent oxidation and ensure good solder wettability, while the inner portion maintains higher Mg concentration (0.03-3 mass%) to provide mechanical strength and electrical conductivity. This spatial differentiation of Mg concentration resolves the contradiction between strength improvement and reliability maintenance.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent segments the copper alloy plate into two distinct regions: a surface layer and an inner portion, each with different Mg concentration ranges. This segmentation allows the surface layer to optimize for soldering performance while the inner portion optimizes for mechanical and electrical properties, thereby resolving the contradiction between strength enhancement and connection reliability.

Inventive Principle:

Principle #1Segmentation

2Reliability

If Sn plating and heating treatment is performed to improve electrical connection reliability, then connection reliability is improved, but solder wettability and plating film adhesiveness deteriorate due to Mg diffusion into plating film

Engineering Contradiction:

Improveelectrical connection reliabilityVSAvoidplating film peeling

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent applies preliminary anti-action by pre-suppressing Mg concentration in the surface layer before plating and heating treatments are performed. By controlling the surface Mg concentration to 10-30 mass ppm in advance, the patent prevents Mg from diffusing into the plating film during subsequent heating processes, thereby avoiding plating film peeling and maintaining good solder wettability while still achieving reliable electrical connections.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The patent implements preliminary action by establishing the desired Mg concentration gradient in the copper alloy plate before plating and heating treatments. This preliminary control of Mg distribution ensures that when plating and heating are subsequently performed, Mg does not diffuse into the plating film, thus preventing adhesiveness deterioration and maintaining plating film integrity.

Inventive Principle:

Principle #10Preliminary action

3Strength

If uniform Mg concentration is maintained throughout the copper alloy plate to ensure mechanical strength, then strength is maintained, but surface oxidation occurs leading to poor solder wettability

Engineering Contradiction:

Improvemechanical strengthVSAvoidsurface oxidation

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

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 solder wettability and adhesiveness of the plating film, maintaining mechanical characteristics and reducing the risk of plating film peeling, thereby enhancing electrical connection reliability.

Implementation Method 1

Mg is easy to be diffused to the surface of the plating film by heating

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 2

Mg on the surface of the copper alloy plate before plating becomes oxide Mg immediately

Methodology Applied

Scientific EffectOxidation: Oxidation

Implementation Method 3

formed using electrolytic plating with specific current density

Methodology Applied

Scientific EffectElectroplating: Electroplating

Data Source

PatentUS11781234B2Copper alloy plate, plating film-attached copper alloy plate, and methods respectively for manufacturing these products

Publication Date: 2023.10.10 MITSUBISHI MATERIALS CORP

AI summary

A copper alloy plate including 0.3 mass % or more and 1.2 mass % or less of Mg, 0.001 mass % or more and 0.2 mass % or less of P, and the balance Cu with inevitable impurities in a thickness center portion in a plate thickness direction; Mg concentration on a plate surface is 30% or less of bulk Mg concentration at the thickness center portion; a surface layer part having a depth from the plate surface to where it is 90% of the bulk Mg concentration is provided; and in the surface layer part, the Mg concentration increases from the plate surface toward the thickness center portion with a concentration gradient 1.8 mass %/μm or more and 50 mass %/μm or less.