Intrinsic Diffusivities Ratio Analysis in the Al-Cu System

M.V Yarmolenko

doi:10.15330/pcss.21.4.720-726

Abstract

Copper and aluminium electric corrosion rates are investigated experimentally at room temperature and at temperature 100oC. It is founded that copper corrosion is higher than aluminium corrosion, and ratio of electric corrosion rates, kCu/kAl , decreases with temperature increasing. It is calculated that copper corrosion rate is approximately equal to aluminium corrosion at temperature about 300oC due to Cu2+ ions are less mobile than Cu+ ions. It is obvious physically: the higher temperature is, the grater atoms’ displacements in crystal lattice, Cu atoms can diffuse without two electrons, and Cu2+ ions more strongly interact with crystal lattice than Cu+ ions. A theoretical method to calculate intrinsic diffusivities ratio in double multiphase systems is proposed. The method involves the Kirkendall plane displacement and the general phases thickness only. Intrinsic diffusivities ratios in the Al-Cu system are calculated using literature experimental data. Diffusion activation energies and pre-exponential coefficients for the Cu-Al system are calculated combining literature experimental results. Analysis of literature data shows that the Kirkendall shift changes sign at temperature about 460oC in the Cu-Al system because of intrinsic diffusivities ratio, DCu*/DAl*, dependence from temperature. Such result agrees with copper and aluminium electric corrosion rates investigation. 

Highlights

The Cu-clad Al (CA) wire, where the CA wire is an Al wire coated with Cu (≈ 15μm thickness), is widely used for electronic parts as a conductive material in the automobile industry
That copper electric corrosion is higher than aluminium electric corrosion in approximately two times at temperatures less than 40 оС [3, 4], so thin Al layer can prevent copper electric corrosion
Equations 28 correspond to obtained results [14]. it should be Q1 < Q2, Q1 < Q3, and Q3 < Q2 because of K1 > K2, K1 > K3, and K3 > K2 if Copper corrosion is higher than aluminium corrosion, and ratio of electric corrosion rates, kCu/kAl, decreases with temperature increasing

Summary

Introduction

The Cu-clad Al (CA) wire, where the CA wire is an Al wire coated with Cu (≈ 15μm thickness), is widely used for electronic parts as a conductive material in the automobile industry. It was proved experimentally that thin Al pad (≈ 1 μm thickness) can prevent gold and copper corrosion, because intermetallics formation rate in Au-Al system is much more higher than intermetallics formation rate in Cu-Al system, so it is possible to use Cu instead of Au for wire bonding in microelectronics packaging, and Cu has higher electric conductivity, higher thermal conduction, and lower material cost than Au [2] It was founded experimentally, that copper electric corrosion is higher than aluminium electric corrosion in approximately two times at temperatures less than 40 оС [3, 4], so thin Al layer can prevent copper electric corrosion. QAl > QCu because Cu+ ions have higher mobilities than Al3+ ions

Method

Analysis for the Al-Cu system

Findings

Diffusion activation energy calculation in the Cu-Al system