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.
Highlights
IntroductionGas-atomized solder powders are several tens of micrometers small, even smaller solder powders are required to meet the demands of more advanced solder bumps for high microelectronic package loading [3,4,5,6]
Fabricating small-sized solder powders is an essential approach to constituting more compact solder bump arrays, because the solder bump size on a packaging substrate decreases as a result of the miniaturization of electronic components, and the pitch distance drops to the submicron level [1,2]. gas-atomized solder powders are several tens of micrometers small, even smaller solder powders are required to meet the demands of more advanced solder bumps for high microelectronic package loading [3,4,5,6]
Bi–Sn solder system; it predicated on the formation of Ga0.9In0.1, BiIn, and In0.2Sn0.8 intermetallic compounds (IMCs) according to the Ga–In, Bi–In, and In–Sn interfacial reactions
Summary
Gas-atomized solder powders are several tens of micrometers small, even smaller solder powders are required to meet the demands of more advanced solder bumps for high microelectronic package loading [3,4,5,6]. In addition to the gas atomization process, a facile ball-milling process can be used for fabricating smaller-sized solder powders [7]. This method, which imparts high impact energy, can only be applied to brittle materials and is limited to ductile solder powders [7]. During alloy formation, the Bi solder constituent reacts with the Metals 2016, 6, 74; doi:10.3390/met6040074 www.mdpi.com/journal/metals
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