Purpose

The purpose of this paper is to investigate the effect of fullerene (FNS) reinforcements on the microstructure and mechanical properties of 96.5Sn3Ag0.5Cu (SAC305) lead-free solder joints under isothermal ageing and electrical-migration (EM) stressing.

Design/methodology/approach

In this paper, SAC305 solder alloy doped with 0.1 Wt.% FNS was prepared via the powder metallurgy method. A sandwich-like sample and a U-shaped sample were designed and prepared to conduct an isothermal ageing test and an EM test. The isothermal ageing test was implemented under vacuum atmosphere at 150°C, whereas the EM experiment was carried out with a current density of 1.5 × 10⁴ A/cm². The microstructural and mechanical evolutions of both plain and composite solder joints after thermal ageing and EM stressing were comparatively studied.

Findings

A growth of Ag₃Sn intermetallic compounds (IMCs) in solder matrix and Cu-Sn interfacial IMCs in composite solder joints was notably suppressed under isothermal ageing condition, whereas the hardness and shear strength of composite solder joints significantly outperformed those of non-reinforced solder joints throughout the ageing period. The EM experimental results showed that for the SAC305 solder, the interfacial IMCs formulated a protrusion at the anode after 360 h of EM stressing, whereas the surface of the composite solder joint was relatively smooth. During the stressing period, the interfacial IMC on the anode side of the plain SAC305 solder showed a continuous increasing trend, whereas the IMC at the cathode presented a decreasing trend for its thickness as the stressing time increased; after 360 h of stressing, some cracks and voids had formed on the cathode side. For the SAC305/FNS composite solder, a continuous increase in the thickness of the interfacial IMC was found on both the anode and cathode sides; the growth rate of the interfacial IMC at the anode was higher than that at the cathode. The nanoindentation results showed that the hardness of the SAC305 solder joint presented a gradient distribution after EM stressing, whereas the hardness data showed a relatively homogeneous distribution in the SAC305/FNS solder joint.

Originality/value

The experimental results showed that the FNS reinforcement could effectively mitigate the failure risk in solder joints under isothermal ageing and high-current stressing. Specifically, the FNS particles in solder joints can work as a barrier to suppress the diffusion and migration of Sn and Cu atoms. In addition, the nanoidentation results also indicated that the addition of the FNS reinforcement was very helpful in maintaining the mechanical stability of the solder joint. These findings have provided a theoretical and experimental basis for the practical application of this novel composite solder with high-current densities.

中文翻译：

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等温老化和高电流应力下96.5Sn-3Ag-0.5Cu /富勒烯复合焊料的性能

目的

本文的目的是研究在等温老化和电迁移（EM）应力下，富勒烯（FNS）增强剂对96.5Sn3Ag0.5Cu（SAC305）无铅焊点的组织和力学性能的影响。

设计/方法/方法

本文通过粉末冶金法制备了掺杂0.1％（重量）FNS的SAC305钎料合金。设计并制备夹心样样品和U形样品以进行等温老化测试和EM测试。等温老化测试是在150°C的真空环境下进行的，而EM实验是在1.5×10 ⁴  A / cm ²的电流密度下进行的。比较研究了热老化和EM应力作用后的普通和复合焊点的微观结构和力学演变。

发现

Ag ₃的生长在等温老化条件下，焊料基体中的锡金属间化合物（IMC）和复合焊点中的Cu-Sn界面IMC受到显着抑制，而在整个时效期间，复合焊点的硬度和剪切强度明显优于非增强型焊点。EM实验结果表明，对于SAC305焊料，EMC应力360 h后，界面IMC在阳极处形成了突起，而复合焊点的表面相对光滑。在应力期间，普通SAC305焊料阳极侧的界面IMC呈连续增加趋势，而阴极的IMC随应力时间的增加呈现出厚度减小的趋势。经过360小时的压力，在阴极侧形成一些裂纹和空隙。对于SAC305 / FNS复合焊料，在阳极侧和阴极侧都发现界面IMC的厚度连续增加。阳极上的界面IMC的生长速率高于阴极上的。纳米压痕结果表明，SCM305焊点的硬度在EM应力后呈现梯度分布，而硬度数据显示SAC305 / FNS焊点的分布相对均匀。

创意/价值

实验结果表明，FNS增强材料可以有效降低等温老化和大电流应力下焊点的失效风险。具体而言，焊点中的FNS颗粒可作为阻挡层来抑制Sn和Cu原子的扩散和迁移。此外，纳米鉴定结果还表明，添加FNS增强剂对保持焊点的机械稳定性非常有帮助。这些发现为这种新型高电流密度复合焊料的实际应用提供了理论和实验基础。