Purpose

The surface finish is an essential step in printed circuit boards design because it provides a solderable surface for electronic components. The purpose of this study to investigate the effects of different surface finishes during the soldering and ageing process.

Design/methodology/approach

The solder joints of Sn-4.0Ag-0.5Cu/Cu and Sn-4.0Ag-0.5Cu/electroless nickel/immersion silver (ENImAg) were investigated in terms of intermetallic (IMC) thickness, morphology and shear strength. The microstructure and compositions of solder joints are observed, and analyzed by using scanning electron microscopy (SEM-EDX) and optical microscope (OM).

Findings

Compounds of Cu₆Sn₅ and (Cu, Ni)₆Sn₅ IMC were formed in SAC405/Cu and SAC405/ENImAg, respectively, as-reflowed. When the sample was exposed to ageing, new layers of Cu₃Sn and (Ni, Cu)₃Sn₅ were observed at the interface. Analogous growth in the thickness of the IMC layer and increased grains size commensurate with ageing time. The results equally revealed an increase in shear strength of SAC405/ENImAg because of the thin layer of IMC and surface finish used compared to SAC405/Cu. Hence, a ductile fracture was observed at the bulk solder. Overall, the ENImAg surface finish showed excellent performance of solder joints than that of bare Cu.

Originality/value

The novel surface finish (ENImAg) has been developed and optimized. This alternative lead-free surface finish solved the challenges in electroless nickel/immersion gold and reduced cost without affecting the performance.

中文翻译：

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SAC405 / Cu和SAC405 / ENImAg焊点界面的金属间层结构的形成

目的

表面光洁度是印刷电路板设计中必不可少的步骤，因为它为电子元件提供了可焊接的表面。这项研究的目的是研究在焊接和老化过程中不同表面处理的影响。

设计/方法/方法

研究了Sn-4.0Ag-0.5Cu / Cu和Sn-4.0Ag-0.5Cu /化学镍/浸银（ENImAg）的焊点，包括金属间化合物（IMC）的厚度，形貌和剪切强度。观察焊点的微观结构和组成，并使用扫描电子显微镜（SEM-EDX）和光学显微镜（OM）进行分析。

发现

回流时分别在SAC405 / Cu和SAC405 / ENImAg中形成Cu ₆ Sn ₅和（Cu，Ni）₆ Sn ₅ IMC的化合物。当样品经受老化时，在界面处观察到新的Cu ₃ Sn和（Ni，Cu）₃ Sn _5层。IMC层厚度的类似增长和晶粒尺寸的增加与时效时间相对应。结果同样表明，与使用SAC405 / Cu相比，由于使用了IMC薄层和表面光洁度，SAC405 / ENImAg的剪切强度有所提高。因此，在块状焊料处观察到延性断裂。总体而言，ENImAg表面光洁度显示出的焊点性能优于裸铜。

创意/价值

已经开发和优化了新型表面光洁度（ENImAg）。这种替代的无铅表面光洁度解决了化学镀镍/浸金中的挑战，并在不影响性能的情况下降低了成本。