Ultra-short vertically aligned carbon nanofibers transfer and application as bonding material
Artikel i vetenskaplig tidskrift, 2013
Purpose - The transferred carbon nanofibers (CNFs) can be applied in flip chip package as interconnect material, as an alternative to the conventional solder and conductive adhesive (CA) materials. Design/methodology/approach - The structure of CNFs was confirmed by transmission electron microscopy (TEM). The electrical performance of the vertically aligned carbon nanofibers (VACNFs) joint was measured by four points probe method and compared to conventional lead-free solder Sn3.0Ag0.5Cu, pure indium and silver CA. A shear test was carried out in order to evaluate the mechanical performance of VACNFs joint. After the shear test, the fracture surface was analyzed by scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS). Findings - The results showed a high success rate in the transfer of VACNFs from growth chip to target chip. The Au-coated CNF can be wetted well with melted indium during the transfer and bonding process. In-Au intermetallic compound (IMC) formed on the surface of CNF. The electrical and mechanical performance of VACNFs is comparable to that of the traditional interconnect materials. The fracture surface is located at the interface between VACNFs and chips. The stacked-cone structure of CNF can be confirmed from a cross-section of the break CNF by TEM. Originality/value - Ultra-short VACNFs were grown and first successfully transferred to the target chip using a process which required little pressure, low temperature and short time.