Due to the physical limitation of lithography process, industries are now faced with a dilemma of scaling down electronic component size. By using Through-Silicon-Via and Micro-Joints to achieve vertical stack of chips, three-dimensional integrated circuits (3D ICs) is therefore regarded as the savior that is able to extent Moore’s law or even create the era of More-than-Moore. In spite of such a promising prospect for 3D ICs, many issues also arise accompanying with the miniaturization of transistor in micro-bump. For example, solder in a micro joint will react quickly with substrate and then transform totally into intermetallic compound, and the mechanical properties of this joint are thus no longer dominated by solder itself but for IMC. Also, for some sensitive devices like bio-chip or optoelectronic devices will encounter the risk of bond failure due to heat localization at such small volume of electronic components. In order to prevent the failure caused by high temperature bonding process, the development of lead-free low-temperature solder material is of great importance. Indium, whose melting point is only about 156 ℃, can be used to overcome this difficulty. It's also worth mentioning that, indium processes not only low melting point but also high thermal and electrical conductivity, excellent ductility and self-alignment capability. All of these benefits mentioned above make it become one of the most competitive low-temperature solders nowadays. However, studies taking indium as solder material are much less than that of using Sn or Sn-Ag-Cu solder due to its nature softness.
As a result, I choose indium as a low-temperature solder material in my study while commonly-used Ni as substrate material. In this research, the interfacial reaction between solid nickel and liquid indium at 200 ℃, 225 ℃ and 250 ℃ are studied. Since the reliability of micro joints are predominated by intermetallic compounds unlike conventional flip-chip joints or ball grid array (BGA) joints, the mechanical properties of IMC in this Ni-In binary system are also explored by using nanoindenter.