Effect of various Ni plating layers and aging on microstructure and shear strength of Sn–2.5Ag–2.0Ni solder joint Mao Wu ⁎, Xinbo He, Rafi-ud-din, Shubin Ren, Mingli Qin, Xuanhui Qu State Key Laboratory for Advanced Metals and Materials, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China abstract article info Article history: Received 4 November 2008 Accepted in revised form 11 March 2009 Available online 17 March 2009 Keywords: Electroless Ni plating Soldering SiC p /Al composite Aging Intermetallic compound (IMC) Sn–2.5Ag–2.0Ni alloy is used to solder silicon carbide reinforced aluminum matrix (SiC p /Al) composites substrate with various Ni coatings. An experimental study is carried out to assess the effects of various Ni coatings on the microstructure and reliability of solder joint. Three electroless Ni layers, including Ni–5 wt.%P, Ni–10 wt.%P and Ni–B, are investigated. The electroless Ni–B layer is found to have good wettability with solder and gives the lowest growth rate of Ni 3 Sn 4 IMCs during aging. The formation of Ni 2 SnP, which significantly affects the reliability of solder joints, is suppressed by using the low P content Ni–5 wt.%P layer. The electroless Ni–B layer has given the highest shear strength of solder joint while Ni–5 wt.%P layer yields the higher shear strength as compared to Ni–10 wt.%P layer. Growth of Ni 3 Sn 4 IMCs and formation of crack are observed to be the major sources of failure for the solder joint with Ni–5 wt.%P, whereas, the failure of Ni– 10 wt.%P solder joint is accounted for the formation of Ni 2 SnP, P-rich Ni layer and Kirkendall voids after long term aging. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Kovar alloy is one of the important microelectronic packaging materials that has been widely used in military and aerospace areas. However, kovar alloy has some inherent disadvantages such as low thermal conductivity and high density. Metal matrix composite, SiC p / Al composite is an ideal substitute for kovar alloy. SiC p /Al may possess a combination of novel properties, including a thermal expansion coefficient compatible to an electronic device or substrate, high thermal conductivity, low density as well as high mechanical strength. Such a combination of properties makes the composites a valuable packaging material for electronic applications. Main application fields of the material are heat sinks, substrates, enclosures and base plates of various power modules, where requirement for thermal management is high, and at the same time the limitation imposed to weight of the material is stringent. A comprehensive review on the composites, their properties as well as their applications in electronics industry may be found in Ref. [1]. An important beneficial property for these composites is thermal conductivity that can be changed within a wide range by addition of different amounts of SiC particles to the starting powder mixture. Most of the research about SiC p /Al composites revolves around its production techniques and less has been carried out about its post-processing techniques such as welding and heat treatment [1–8]. SiC p /Al composite can replace kovar alloy and is used in making seals and carriers of ceramic package for discrete transistors, diodes and integrated circuits. These package forms should offer accurate component placement, attachment, sealing, protection and various electrical, optical and fluidic interconnects. These assemblies usually have longer shelf-lives and require hermetic sealing. Package sealing can be obtained using a variety of materials including epoxies and solders [9]. Among these, Sn 95.5 Ag 2.5 Ni 2.0 solder is well suited for soldering optoelectronic devices and hermetic sealing applications. In this study, Sn 95.5 Ag 2.5 Ni 2.0 is aimed to join SiC p /Al composites lids and enclosures. In general, Au, Ni and Pt elements are the most common surface finishes selected to be soldered with Sn-based solder. However, the IMC layer tends to grow with time by solid-state diffusion, even at ambient temperatures, that adversely affects on the reliability of solder joints due to the excessive rise in thermal mismatch [10–14]. Ni is well-recognized as a good diffusion barrier between substrate and solder due to its negligible solubility in Sn-based solder as well as low growth rate of Sn–Ni intermetallic [15]. Therefore, conventional surface finishing metallization on the kovar alloy substrate is a Ni/ Au deposition by electroplating. However, it is difficult to deposit Ni layer on the SiC p /Al composites by electroplating due to the existence of the nonmetallic SiC particles. Therefore, an electroless Ni plating process is employed for the metallization of SiC p /Al composites. This process has the advantages of low cost, simple facility and conformal deposition of metallic coatings on complex components. In the case of electroless plating, SiC p /Al composites are metallized by exposing to plating solutions in the presence of a reductant. The electroless Ni–P is an important electroless deposition alloy in electronic and semicon- ductor device industries due to its excellent corrosion resistance, solderability, thermal stability and electrical property. During the Surface & Coatings Technology 203 (2009) 3011–3018 ⁎ Corresponding author. E-mail address: wumao1981@yahoo.cn (M. Wu). 0257-8972/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2009.03.014 Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat