Nanocopper Based Solder-Free Electronic Assembly

Abstract

CuantumFuse nano copper material has been used to assemble functional LED test boards and a small camera board with a 48 pad CMOS sensor quadflat no-lead chip and a 10 in flexible electronics demo. Drop-in replacement of solder, by use of stencil printing and standard surface mount technology equipment, has been demonstrated. Applications in space and commercial systems are currently under consideration. The stable copper-nanoparticle paste has been examined and characterized by scanning electron microscopy and high-resolution transmission electron microscopy; this has shown that the joints are nanocrystalline but with substantial porosity. Assessment of reliability is expected to be complicated by this and by the effects of thermal and strain-enhanced coarsening of pores. Strength, creep, and fatigue properties were measured and results are discussed with reference to our understanding of solder reliability to assess the potential of this nano-copper based solder alternative.

Novel approach to copper sintering using surface enhanced brass micro flakes for microelectronics packaging

“…In addition, the higher melting point of Cu (1085 °C) would mean a higher sintering temperature compared to Ag, when working with particles of comparable morphologies. Solutions to tackle these challenges in Cu sintering range mainly from using reducing atmosphere (H2 or formic acid enriched N2) during sintering [7][8][9][10], using reducing binders in pastes [11,12], oxidationreduction bonding processes [13], Cu core shell particles with Ag/Sn outer layers [14,15] and phosphating Cu nanoparticles [16]. While these solutions are promising at laboratory scale experiments, the high sintering temperatures (> 300 °C) and the intensive and expensive process of development of Cu nanoparticles are challenges in upscaling to real-world applications.…”

Enhanced copper micro/nano-particle mixed paste sintered at low temperature for 3D interconnects

“…9 Thus, various aspects of copper nanoparticles paste used for interconnects formation are actively studied as reported by Tan and Cheong 11 and Yamakawa et al 12 However, several studies have consistently reported the issue of mechanical cracking in the joints formed by copper nanoparticles paste which results in low bond strength and reliability. 13,14 Cracks persist during paste drying partly because of the densification stress imposed by solvents evaporation. Soft particles tend to deform and form pores, while hard particles develop cracks to release stress.…”

Investigation of nano-copper for electronic packaging application : solder metallization and die attach

“…These detached particles or layers of particles will eventually react with Sn under extended reflow time. As has been studied by Schnabl, the sintered NC has porous structure and nano-size grains [46]. This porous structure is not very dense and some of them have cracks on the surface.…”

“…The FIB-polished NC sample is shown in Figure 2.9. The porous structure gives sintered NC better failure resistance, though its fatigue failure is brittle type like IMC (Intermetallic) failure [46]. In the future, more investigation is needed for the properties of porous NC and other porous metals [45].…”

“…Martin Advanced Technology Center. This paste has also been studied in K. Schnabl et al [46]. The raw CuantumFuse TM Paste has to be washed before utilization.…”