The impact of paste alloy, paste volume, and surface finish on solder joint

IF 1.6 4区工程技术 Q3 ENGINEERING, ELECTRICAL & ELECTRONIC Microelectronics Reliability Pub Date : 2024-07-24 DOI:10.1016/j.microrel.2024.115457

Abdallah Alakayleh , Sa'd Hamasha , Ali Alahmer

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Abstract

The reliability of solder joints is significantly influenced by the microstructure of SAC (Sn-Ag-Cu) solders, which is affected by various factors, including paste alloy, paste volume, and surface finish. This study explores the impact of these factors on the microstructure, thickness of the intermetallic compound (IMC) layer, hardness, and macro void presence in as-reflowed joints. Three lead-free solder alloys, namely SAC305 (Sn - 3.0Ag - 0.5Cu), SAC-Bi (Sn - 3.0Ag - 3.0Bi - 0.8Cu), and SAC-Bi-Sb (Sn - 3.4Ag - 3.2Bi - 3.0Sb - 0.7Cu), were tested with varying solder paste-to-sphere ratios with electroless nickel immersion gold (ENIG) and organic solderability preservative (OSP) surface finishes. ENIG involves applying a thin layer of gold over a layer of nickel on the copper surfaces. Whereas OSP is a thin organic coating designed to protect copper surfaces from oxidation. The evaluation incorporated the analysis of Ag₃Sn particles, IMC thickness, and voids through scanning electron and optical microscopy and X-ray images. Additionally, microhardness was assessed by indenting seven solder joints using the Phase II Model 900–391,391 micro-Vickers hardness tester. The study revealed that the SAC305 exhibited a higher presence of Ag₃Sn particles than SAC-Bi and SAC-Bi-Sb. A direct proportionality was observed between paste volume and the quantity of Ag₃Sn particles. Conversely, an inverse relationship was identified between paste volume and IMC layer thickness, resulting in a thinner IMC layer with higher paste volume, regardless of the paste alloy used. Furthermore, the use of ENIG led to a reduction in IMC thickness, attributed to the inhibitory effect of the Ni barrier. Doped alloys, specifically SAC-Bi and SAC-Bi-Sb, displayed superior microhardness compared to SAC305, owing to the strengthening and hardening effects of Bi and Sb. Regarding solder voiding, a noteworthy observation indicated that an increase in the quantity of solder paste resulted in the formation of larger voids.

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锡膏合金、锡膏量和表面光洁度对焊点的影响

SAC（锡-银-铜）焊料的微观结构对焊点的可靠性有很大影响，而微观结构又受多种因素的影响，包括焊膏合金、焊膏量和表面光洁度。本研究探讨了这些因素对回流焊点的微观结构、金属间化合物（IMC）层厚度、硬度和宏观空隙存在的影响。测试了三种无铅焊料合金，即 SAC305（Sn - 3.0Ag - 0.5Cu）、SAC-Bi（Sn - 3.0Ag - 3.0Bi - 0.8Cu）和 SAC-Bi-Sb（Sn - 3.4Ag - 3.2Bi - 3.0Sb - 0.7Cu），测试时采用了不同的焊膏与球体比率，以及无电解镍浸金（ENIG）和有机可焊性防腐剂（OSP）表面处理。ENIG 是在铜表面的镍层上镀一薄层金。而 OSP 是一种薄薄的有机涂层，旨在保护铜表面免受氧化。评估包括通过扫描电子显微镜、光学显微镜和 X 射线图像分析 AgSn 颗粒、IMC 厚度和空隙。此外，还使用第二阶段 900-391,391 型显微维氏硬度计对七个焊点进行了压痕测试，以评估其显微硬度。研究显示，与 SAC-Bi 和 SAC-Bi-Sb 相比，SAC305 显示出更高的 AgSn 颗粒含量。浆料体积与 AgSn 颗粒数量之间呈正比关系。相反，浆料体积与 IMC 层厚度之间存在反比关系，无论使用何种浆料合金，浆料体积越大，IMC 层越薄。此外，ENIG 的使用导致 IMC 厚度减小，这归因于镍屏障的抑制作用。与 SAC305 相比，掺杂合金（特别是 SAC-Bi 和 SAC-Bi-Sb）显示出更高的显微硬度，这归因于 Bi 和 Sb 的强化和硬化效应。在焊料空洞方面，一个值得注意的观察结果表明，焊膏数量的增加会导致形成更大的空洞。

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来源期刊

Microelectronics Reliability 工程技术-工程：电子与电气

CiteScore

3.30

自引率

12.50%

发文量

342

审稿时长

68 days

期刊介绍： Microelectronics Reliability, is dedicated to disseminating the latest research results and related information on the reliability of microelectronic devices, circuits and systems, from materials, process and manufacturing, to design, testing and operation. The coverage of the journal includes the following topics: measurement, understanding and analysis; evaluation and prediction; modelling and simulation; methodologies and mitigation. Papers which combine reliability with other important areas of microelectronics engineering, such as design, fabrication, integration, testing, and field operation will also be welcome, and practical papers reporting case studies in the field and specific application domains are particularly encouraged. Most accepted papers will be published as Research Papers, describing significant advances and completed work. Papers reviewing important developing topics of general interest may be accepted for publication as Review Papers. Urgent communications of a more preliminary nature and short reports on completed practical work of current interest may be considered for publication as Research Notes. All contributions are subject to peer review by leading experts in the field.