Purpose

This study aims to investigate the effect of bismuth addition (up to 30 Wt%) on the microstructure and electrical conductivity of a commercial lead-free alloy (SAC405) near the solder/substrate soldered joint. The system under study is referred in this work as (SAC405 + xBi)/Cu, as Cu is the selected substrate in which the solder was casted. The electrical resistivity of this system was investigated, considering Bi addition effect on the local microstructure and chemical composition gradients within that zone.

Design/methodology/approach

Solder joints between Cu substrate and SAC405 alloy with different levels of Bi were produced. The electrical conductivity along the obtained solder/substrate interface was measured by four-point probe method. The microstructure and chemical compositions were evaluated by scanning electron microscopy/energy dispersive spectroscopy analysis.

Findings

Two different electrical resistivity zones were identified within the solder interface copper substrate/solder alloy. At the first zone (from intermetallic compound [IMC] until approximately 100 μm) the increase of the electrical resistivity is gradual from the substrate to the solder side. This is because of the copper substrate diffusion, which established a chemical composition gradient near the IMC layer. At the second zone, electrical resistivity becomes much higher and is mainly dependent on the Bi content of the solder alloy. In both identified zones, electrical resistivity is affected by its microstructure, which is dependent on Cu and Bi content and solidification characteristics.

Originality/value

A detailed characterization of the solder/substrate zone, in terms of electrical conductivity, was done with the definition of two variation zones. With this knowledge, a better definition of processing parameters and in-service soldered electronic devices behavior can be achieved.

中文翻译：

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Bi的添加对SAC405焊接结构的电和微观结构性能的影响

目的

这项研究的目的是研究添加铋（最高30 Wt％）对靠近焊料/基板焊接点的商用无铅合金（SAC405）的微观结构和电导率的影响。在这项工作中，正在研究的系统称为（SAC405 + xBi）/ Cu，因为Cu是铸造焊料的选定衬底。考虑到Bi添加对该区域内局部微观结构和化学成分梯度的影响，研究了该系统的电阻率。

设计/方法/方法

在铜基体和具有不同Bi含量的SAC405合金之间建立了焊点。沿着获得的焊料/基板界面的导电率通过四点探针法测量。通过扫描电子显微镜/能量色散光谱分析法评价其微观结构和化学组成。

发现

在焊料界面铜基板/焊料合金中确定了两个不同的电阻率区域。在第一个区域（从金属间化合物[IMC]直到大约100μm），电阻率的增加是从基板到焊料侧的。这是由于铜基板的扩散，在IMC层附近建立了化学成分梯度。在第二区域，电阻率变得更高，并且主要取决于焊料合金的Bi含量。在两个确定的区域中，电阻率均受其微观结构的影响，微观结构取决于Cu和Bi的含量以及凝固特性。

创意/价值

根据两个导电区域的定义，对焊料/基板区域的导电性进行了详细的表征。有了这些知识，就可以更好地定义加工参数和使用中的焊接电子设备的性能。