Materials Science and Engineering B60 (1999) 112 – 117 Chemical synthesis and properties of nanocrystalline Cu – Fe – Ni alloys J. Stolk *, A. Manthiram Texas Materials Institute, ETC 9.104, The Uniersity of Texas at Austin, Austin, TX 78712, USA Received 8 October 1998; received in revised form 25 January 1999; accepted 1 February 1999 Abstract The chemical reduction of Cu 2 + , Fe 3 + , and Ni 2 + ions with sodium borohydride in aqueous solution followed by heat treatments at 300–900°C in a H 2 atmosphere was investigated to obtain nanocrystalline Cu – Fe – Ni, which may have low thermal expansion and enhanced thermal and electrical conductivities. The samples were characterized by X-ray diffraction, optical microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, thermomechanical analysis, and electrical conductivity measurements. Thermal conductivity was estimated using the Wiedemann – Franz law. Sintering lead to the formation of a Cu-rich phase and a  –(Fe, Ni) Invar phase. The growth and stability of the Cu and  –(Fe, Ni) Invar phases and the effects of composition on the properties of Cu – Fe – Ni alloys were investigated. © 1999 Elsevier Science S.A. All rights reserved. Keywords: Synthesis; Properties; Nanocrystalline Cu – Fe – Ni alloys 1. Introduction One of the greatest challenges facing the microelec- tronics industry is the thermal expansion mismatch among the materials used in electronic devices and components. Differences in the coefficients of thermal expansion (CTE) may result in high interfacial shear strains and premature failure of electronic assemblies. The problem lies in the inherent difference in the CTE of metallic versus nonmetallic materials. A particular problem that plagues the electronics industry is the fatigue failure of solder joints due to a CTE mismatch between the printed wiring boards (PWB) and surface- mounted components such as leadless ceramic chip carriers (LCCC) and high performance flip chips, which are mounted directly to the PWB without the use of a ceramic package. Low CTE metals or alloys such as Invar offer one possible solution to the CTE mismatch problem by effectively reducing the thermal expansion mismatch between the surface components and the printed wiring boards during thermal cycling of the board assembly. The disadvantage of these materials is that they typi- cally have low thermal and electrical conductivities and cause additional problems in heat dissipation and cur- rent flow. In order to take advantage of low CTE materials, much attention is now focused on con- strained core technology (CCT), in which composites are produced from a combination of materials with low CTE and materials with high conductivity. The result is a structure with balanced properties that can effectively serve as both a core constraining material and a heat dissipation path. Among the materials examined for use in CCT applications are clad or roll-bonded copper – In- var–copper (CIC) [1–3], extruded copper–Invar pow- der composites [4], copper-infiltrated tungsten or molybdenum powder metallurgy (PM) composites [5], silver – Invar [6], composites of copper with titanium – nickel [7], beryllium – beryllia [6], and a variety of metal – ceramic composites [6,8]. Many of these core- constraining materials are currently available in com- mercial multilayer circuit boards. Although many layered or PM composites offer at- tractive properties, their manufacturing or material costs can often be quite high. Homogeneous alloys of Cu, Fe, and Ni may offer an attractive alternative to the composites currently used to lower the CTE of printed wiring boards. The Cu–Fe–Ni ternary phase * Corresponding author. 0921-5107/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII:S0921-5107(99)00022-7