Sn-0.5Cu(-x)Al Solder Alloys: Microstructure-Related Aspects and Tensile Properties Responses

Thiago Lima,Crystopher Brito,Bismarck Silva,Clarissa Da Cruz,José Spinelli,Rudimylla Da Silva Septimio,Guilherme De Gouveia,Noé Cheung

doi:10.3390/met9020241

Abstract

In this study, experiments were conducted to analyze the effect of 0.05 and 0.1 wt.% Al additions during the unsteady-state growth of the Sn-0.5wt.%Cu solder alloy. Various as-solidified specimens of each alloy were selected so that tensile tests could also be performed. Microstructural aspects such as the dimensions of primary, λ1, and secondary, λ2, dendritic arrays, and intermetallic compounds (IMCs) morphologies were comparatively assessed for the three tested compositions, that is, Sn-0.5wt.%Cu, Sn-0.5wt.%Cu-0.05wt.%Al, and Sn-0.5wt.%Cu-0.1wt.%Al alloys. Al addition affected neither the primary dendritic spacing nor the types of morphologies identified for the Cu6Sn5 IMC, which was found to be either globular or fibrous regardless of the alloy considered. Secondary dendrite arm spacing was found to be enlarged and the eutectic fraction was reduced with an increase in the Al-content. Tensile properties remained unaffected with the addition of Al, except for the improvement in ductility of up to 40% when compared to the Sn-0.5wt.%Cu alloy without Al trace. A smaller λ2 in size was demonstrated to be the prime microstructure parameter associated with the beneficial effect on the strength of the Sn-0.5wt.%Cu(-x)Al alloys.

Highlights

Solder alloys play a crucial role in the reliability of electronic systems
A number of studies related to the relationship of the microstructure–mechanical properties of solder alloys can be found in the literature [13,23,24], studies on the Sn–Cu–Al alloy system reporting on the microstructural development and resulting mechanical properties have not been developed far in the literature, especially in the case of high cooling rates
The aim of this investigation was to perform a systematic study to show the connection between cooling rate, microstructure, and the tensile response of the Sn-0.5wt.%Cu-xwt.%Al (x = 0.05 and 0.1 Al) solder alloys obtained through transient directional solidification using a water-cooled directional solidification system

Summary

Introduction

Solder alloys play a crucial role in the reliability of electronic systems. these alloys must provide a set of properties to fulfill both the mechanical and electrical demands, but should not increase the cost-effective production of electronic assemblies. A number of studies related to the relationship of the microstructure–mechanical properties of solder alloys can be found in the literature [13,23,24], studies on the Sn–Cu–Al alloy system reporting on the microstructural development and resulting mechanical properties have not been developed far in the literature, especially in the case of high cooling rates The aim of this investigation was to perform a systematic study to show the connection between cooling rate, microstructure, and the tensile response of the Sn-0.5wt.%Cu-xwt.%Al (x = 0.05 and 0.1 Al) solder alloys obtained through transient directional solidification using a water-cooled directional solidification system. This method allowed for a wide range of cooling rates to be investigated in a single experiment including those typical in soldering practice

Experimental Procedure

Solidification Thermal Parameters and Macrosegregation Profiles

Experimental plots theSn–Cu–Al

Dendritic Arrays and Their Evolutions along the Length of the Alloys Castings

Cu6 Sn5 Morphology

Conclusions