镀Sn-3.0Ag-0.5Cu钎料/Co-P与镀Ni-Co-P的界面反应

T. Daito, H. Nishikawa, T. Takemoto, T. Matsunami
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引用次数: 1

摘要

为了应对健康和安全问题,无铅焊接已成为电子封装中的一种流行技术。与含铅焊料相比,日本广泛使用的Sn- 3.0质量% ag -0.5质量%Cu (SAC,除特别注明外均为质量%)焊料的冲击可靠性较低,这是由于焊料合金硬度高,在界面处产生较高的应力集中。一般来说,冲击可靠性与焊接/碰撞冶金(UBM)界面上形成的反应层的形貌和厚度之间存在相关性。最常见的UBM是在铜衬垫上化学镀镍磷。化学镀镍磷作为铜和焊料之间的扩散阻挡层。然而,由于镍的扩散,在焊料和化学Ni-P之间的界面形成富p层。焊点的失效与这些层的生长和脆性有关,影响焊点的机械可靠性。最近,一种新的UBM组成被提出作为扩散屏障(1-4)。例如,Magagnin等人报道,与化学镀Ni-P和Sn-Ag-Cu合金相比,化学镀Co-P强烈限制了相互扩散和金属间化合物的形成。此外,Co-P样品在界面处没有形成富p层(4)。研究反应层形貌与UBM之间的关系具有重要意义。本研究旨在阐明Co-P和Ni-Co-P对钎料/UBM界面反应层形貌的影响。2. 本研究采用实验SAC焊料(0.3 g)。在FR-4 pcb (25.0×25.0×1.6 mm)上制备了化学Co-P(Au) (3.1 Pm)和化学Ni-Co-P(Au) (5.2 Pm)成品Cu板。化学镀Ni-P(Au) (5.0 Pm)衬底也被用作基准衬底。这些衬底被镀金以避免钴和镍表面氧化。实验过程如图1所示,将底物浸泡在4%盐酸溶液中120秒,然后用去离子水冲洗。然后,将焊料置于衬底中央,并将活性助焊剂(0.01 ml)滴在焊料上。将试样置于氮气气氛下的辐射炉中,按照图2所示的温升曲线进行加热。回流峰温度为513 K,样品在490 K以上停留115 s。焊接后,用光学显微镜(OM)测量焊料在UBM上的扩散面积。进行了三次测试,以获得每个样品的平均值。然后,切割试样,并对试样的横截面进行抛光,观察焊料与UBM的界面。用扫描电镜观察了界面处的反应层。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Interfacial reaction between Sn-3.0Ag-0.5Cu solder/Co-P plating and Ni-Co-P plating
In response to health and safety concerns, lead-free soldering has become a popular technology in electronics packaging. Compared with the lead-containing solders, Sn- 3.0mass%Ag-0.5mass%Cu (SAC, all mass% unless specified otherwise) solder widely used in Japan has a relatively low impact reliability owing to the solder alloy hardness that induces a high stress concentration at the interface. In general, there is a correlation between the impact reliability and the morphology and thickness of the reaction layer formed at the solder/under bump metallurgy (UBM) interface. The most common UBM is electroless Ni-P plating over copper pad. Electroless Ni-P acts as a diffusion barrier layer between the copper and the solder. However, due to nickel diffusion, P-rich layers form at the interface between the solder and electroless Ni-P. Solder joint failure is related to the growth of these layers and to their brittleness and affects the mechanical reliability of joints. Recently, a new composition of UBM is proposed as diffusion barrier 1-4) . For instance, Magagnin et al. reported that electroless Co-P strongly limits interdiffusion and intermetallic compounds formation as compared with the electroless Ni-P with Sn-Ag-Cu alloy. Furthermore, in the Co-P samples, P-rich layers did not form at the interface 4) . It is important to investigate the relationship between morphology of reaction layer and UBM. This study aims to clarify the effect of Co-P and Ni-Co-P on the morphology of reaction layer formed at the solder/UBM interface. 2. Experimental SAC solder (0.3 g) was used in this study. Electroless Co-P(Au) (3.1 Pm) and electroless Ni-Co-P(Au) (5.2 Pm) finished Cu plates on FR-4 PCBs (25.0×25.0×1.6 mm) were prepared as UBM. Electroless Ni-P(Au) (5.0 Pm) substrate was also used as a reference substrate. These substrates were plated with gold to avoid oxidation of the cobalt and nickel surface. The experimental procedure is shown in Fig. 1 .T he substrate was immersed in 4% HCl solution for 120 s and then rinsed with deionized water. Then, solder was put on the center of the substrate and activated flux (0.01 ml) was dropped on the solder. The test specimen was put into a radiation furnace in a nitrogen atmosphere and heated according to the temperature rise profile shown in Fig. 2. The reflow peak temperature was 513 K with the sample above 490 K for 115 s. After soldering, the spreading area of the solder on the UBM was measured by using the optical microscope (OM).�Three tests were conducted to obtainan average value for each specimen. Then, specimens were cut and the cross-section of the specimens was polished to observe the interface between the solder and UBM. The reaction layer at the interface was observed by scanning electron microscope (SEM).
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