Abstract
Multi-walled carbon nanotube (MWCNT)/indium–tin–bismuth (In–Sn–Bi) composite nanostructures in which In–Sn–Bi nanoparticles have been penetrated by the MWCNT arrays were synthesized using a chemical reduction method. The incorporation of 0.6 wt% MWCNTs with high electrical conductivity into the In-based solder resulted in low minimum electrical resistivity (19.9 ± 1.0 µΩ·cm). Despite being reflowed at the relatively low temperature of 110 °C, the composite solder nanostructures were able to form mechanically stable solder bumps on a flexible polyethylene terephthalate (PET) substrate due to the MWCNT arrays with a high thermal conductivity of 3000 W/(m·K) and In–Sn–Bi nanoparticles with a low melting temperature of 98.2 °C. Notably, the composite solder bumps exhibited high flexibility (17.7% resistance increase over 1000 cycles of operation in a bending test) and strong adhesion strength (0.9 N average shear strength in a scratch test) on the plastic substrate because of the presence of mechanically flexible and strong MWCNTs dispersed within the solder matrix materials. These overall properties are due to the improved diffusivity of the composite solder nanostructures by the cover of the In–Sn–Bi nanoparticles along the MWCNT arrays and the network structure formation of the composite solder bumps.
Highlights
The ever-rising demand for slim, compact, and lightweight electronic components in flexible microelectronic packaging requires more advanced solder bumps with higher electrical and thermal performance, and stronger mechanical strength[1,2,3,4,5,6,7,8]
Novel Multi-walled carbon nanotube (MWCNT)/In–Sn–Bi composite nanostructures of incorporated MWCNT arrays with high electrical and thermal conductivity and reinforced In–Sn–Bi nanoparticles with a low melting temperature of 98.2 °C were synthesized using a chemical reduction method for attachment to a flexible polyethylene terephthalate (PET) substrate
The composite solder with 0.6 wt% MWCNTs achieved low electrical resistivity (19.9 ± 1.0 μΩ·cm) because MWCNTs behaved like an “express tunnel” for rapid electron transfer in contrast with the “turbulent traffic” of the In–Sn–Bi reference solder with much higher electrical resistivity (36.0 ± 0.7 μΩ·cm)
Summary
The ever-rising demand for slim, compact, and lightweight electronic components in flexible microelectronic packaging requires more advanced solder bumps with higher electrical and thermal performance, and stronger mechanical strength[1,2,3,4,5,6,7,8]. Many studies have focused on their interfacial interactions because the difference in the work function between the MWCNT arrays and the solder constituents gives rise to an electron-transfer barrier that impedes electron tunneling, causing high contact resistance[18] There is another challenge which must be overcome to increase the reactivity of the MWCNT arrays to the solder constituents; due to the chemical inertness of MWCNTs along with low reactivity and poor diffusivity, their surfaces bond weakly with solder constituents necessary for promoting the interconnectability of electronic components[19]. These issues have been severely restricting factors for many potential applications of composite solders (including carbon nanotubes) requiring good electrical conductivity and adhesive properties. We demonstrated via bending and scratch tests that the formation of a network structure of composite solder bumps is a key mechanism in revealing their high flexibility and strong adhesive strength when reflowed on the flexible PET substrate
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