Preparation of Property-Controlled Bi-Based Solder Powders by a Ball-Milling Process

Abstract

Three kinds of Bi-based solder powders with different chemical compositions of binary Bi-Sn, ternary Bi-Sn-In, and quaternary Bi-Sn-In-Ga were prepared using a gas atomization process and subsequently ball-milled for smaller-size fabrication. In particular, only the quaternary Bi-Sn-In-Ga solder powders were severely broken to the size of less than 10 µm in a polyhedral shape due to the presence of the constitutional element, the degree of overall oxidation, and the formation of solid solution, which had affected the fractured extent of the Ga-containing solder powders. Furthermore, a melting point also decreased by the addition of In and/or Ga into the binary Bi-Sn solder system, resulting in a melting point of 60.3˝C for the Bi-Sn-In-Ga solder powders. Thus, it was possible that fractured Bi-Sn-In-Ga solder powders were appropriate for the adhesion of more compact solder bump arrays, enabling reflowing at the low temperature of 110˝C on a flexible polyethylene terephthalate (PET) substrate.

Low Melting Temperature Solder Materials for Use in Flexible Microelectronic Packaging Applications

“…For example, the formation of an eutectic alloy with 42 wt.% Sn and 58 wt.% Bi can lead to a melting point decrease to 138°C due to the shift to the eutectic temperature [3,4]. Due to the melting point drop according to the size decrease, the size reduction effect can also be used to synthesize a low melting point solder [4].…”

“…To be specific, two types of Bi-based micropowders, composed of binary Bi-Sn and ternary merits, including high wetting behavior, large creep resistance, and low coefficient of thermal expansion [12][13][14]. However, the relatively low mechanical strength and melting temperature (138°C) of these materials require improvement for their more effective use in flexible interconnection applications [3,15]. Comparatively, Sn-In solder, which has a low melting temperature (118 °C), has excellent electrical and thermal properties [12,16].…”

“…Ternary Bi-Sn-In micropowders and nanoparticles were prepared as a composite solder material via gas atomization process and a chemical reduction method, respectively [3,4]. To be specific, two types of Bi-based micropowders, composed of binary Bi-Sn and ternary merits, including high wetting behavior, large creep resistance, and low coefficient of thermal expansion [12][13][14].…”

“…Bi-based solder powders with three chemical compositions (binary Bi-Sn, ternary Bi-Sn-In, and quaternary Bi-Sn-In-Ga alloy systems) were fabricated using a gas atomization technique; subsequently, the powders were further ball-milled to fabricate smaller-sized particulates; in particular, the diameter of those in the Bi-Sn-In-Ga powders became less than 10 μm with an irregular shape due to the nature of intrinsic brittleness, the degree of surface oxidation, and the formation of Ga intermetallic compound (IMC), all of which produced fractures of the Ga-containing powders [3].…”

“…In particular, the use of wearable devices requires the development of novel solders that can be reflowed at low temperature to avoid thermal damage to the usually temperature-sensitive components in these flexible devices, such as organic light-emitting diodes (OLEDs), polymer light-emitting diodes (PLEDs), and so on [3][4][5][6]. Thus, it is worthwhile to design a low melting temperature solder for more advanced interconnection technology and thus to impart more reliability to the solder bumps between future organic-or polymer-based microchips and flexible substrates.…”