Hongjin Jiang

Low temperature carbon nanotube film transfer via conductive polymer composites

A low temperature process for transferring carbon nanotube (CNT) film from a silicon wafer to a copper surface via conductive polymer composites is proposed. The morphologies and electrical properties of the transferred CNT films were studied. An ohmic contact was formed between a CNT film and a highly conductive polymer composite and the resistance of the as-transferred CNT film was 0.08 Ω, while a semiconductor joint was formed between a CNT film and a high resistivity polymer composite.

Synthesis of Ag-Cu alloy nanoparticles for lead-free interconnect materials

Silver-copper alloy nanoparticles were synthesized via the polyol process in preparation for the conductive fillers in electrically conductive adhesives. UV absorption and TEM observations showed that the synthesized silver-copper nanoparticles had a randomly mixed alloy structure rather than a core-shell structure, although bulk silver and copper cannot form a solid solution at room temperature.

Ultra high conductivity of isotropic conductive adhesives

Electrical properties of the isotropic conductive adhesives filled with micron sized silver flakes and nanosized silver particles were investigated. By using appropriate surfactants, the resistivity of the silver flakes and silver nanoparticles incorporated conductive adhesives was dramatically reduced to as low as 5 times 10-6 Omega.cm. Morphology studies showed that the decreased resistivity resulted from the sintering of silver nanoparticles. The contact resistance of the conductive adhesives under 85degC/85%RH was significantly stable with respect to aging time due to the further sintering of silver nanoparticles

Carbon fibers from poly (p-phenylene benzobisthiazole) (pbzt) fibers: conversion and morphological aspects

Abstract Conversion of highly oriented stiff-chain Poly ( p -phenylene benzobisthiazole) (PBZT) fibers to carbon fibers was investigated in both batch and continuous processes. The PBZT-based carbon fiber shows a structure somewhat different from those of conventional carbon fibers, with well-defined fibrils and micro-fibrils oriented along the fiber direction. There exists also a sheath-core structure. The fiber surface shows a large amount of microvoids. These morphological features appear to be directly related to features in the precursor fibers. The prospects for producing useful new carbon fiber morphologies from these precursors are discussed.

Thermal Conductivity Enhancement of Epoxy Composites by Interfacial Covalent Bonding for Underfill and Thermal Interfacial Materials in Cu/Low-K Application

Nowadays with enhanced performance and reduced profile, electronics and photonics devices demand efficient heat dissipation and low operation temperature. Thereby, instead of traditional fillers (e.g., fused silica), thermally conductive silicon carbide (SiC) particles and multiwall carbon nanotubes (MWNTs) are applied here as fillers in composites for underfill and thermal interfacial materials (TIMs), respectively. SiC particles are coated with an ultrathin layer of silicon oxide by thermal oxidation at 800°C in air and consequently functionalized by γ-glycidoxypropyl-trimethoxysilane in order to graft epoxides on their surface. Moreover, MWNTs were chemically functionalized with carboxyls and hydroxyls in a concentrated acid mixture. Transmission electron microscopy, Fourier-transform infrared spectrascopy, and thermogravimetric analysis characterization indicates that both of the fillers are successfully functionalized, which makes their surface reactive with epoxy resin, resulting in interfacial covalent chemical bonding between the thermally conductive fillers and epoxy resin. It is found that interfacial chemical bonding across the interface between these functionalized fillers and polymer matrix can promote significant thermal conductivity enhancement of epoxy composites, which is promising for underfill and TIMs in Cu/low-K application.

Tin/silver/copper alloy nanoparticle pastes for low temperature lead-free interconnect applications

Chemical reduction methods were used to synthesize tin/silver/copper (SnAgCu) alloy nanoparticles with various sizes. The thermal properties of the SnAgCu alloy nanoparticles were studied by differential scanning calorimetry. Both the particle size dependent melting temperature and latent heat of fusion have been observed. The as-synthesized SnAgCu alloy nanoparticles were dispersed into an acidic type flux to form the nano solder pastes. Their wetting properties on the cleaned copper surface were studied. It was found that the nanoparticle pastes completely melted and wetted on the copper surface and the tin and copper intermetallic compounds formed. These low melting point SnAgCu alloy nanoparticles could be used for low temperature lead-free interconnect applications.

A Novel Nanocomposite With Photo-Polymerization for Wafer Level Application

A novel nanocomposite photo-curable material which can act both as a photoresist and a stress redistribution layer applied on the wafer level was synthesized and studied. In the experiments, 20-nm silica fillers were modified by a silane coupling agent through a hydrolysis and condensation reaction and then incorporated into the epoxy matrix. A photo-sensitive initiator was added into the formulation which can release cations after ultraviolet exposure and initiate the epoxy crosslinking reaction. The photo-crosslinking reaction of the epoxy made it a negative tone photoresist. The curing reaction of the nanocomposites was monitored by a differential scanning calorimeter with the photo-calorimetric accessory. The thermal mechanical properties of photo-cured nanocomposites thin film were also measured. It was found that the moduli change of the nanocomposites as the filler loading increasing did not follow the Mori-Tanaka model, which indicated that the nanocomposite was not a simple two-phase structure as the composite with micron size filler. The addition of nano-sized silica fillers reduced the thermal expansion and improved the stiffness of the epoxy, with only a minimal effect on the optical transparency of the epoxy, which facilitated the complete photo reaction in the epoxy.

Low Temperature Carbon Nanotube Film Transfer via Conductive Adhesives

A low temperature process for transferring carbon nanotube (CNT) film from a silicon wafer to a copper surface via conductive adhesives is proposed. Both the close-and open-ended CNT films were successfully transferred to a desirable substrate. The morphologies and electrical properties of the transferred CNT films were studied. An ohmic contact was formed between a CNT film and a highly conductive adhesive, while a semiconductor joint was formed between a CNT film and a high resistivity adhesive.

Novel Nonconductive Adhesives/Films With Carbon Nanotubes for High-Performance Interconnects

Novel nonconductive adhesives/films (NCAs/NCFs) with carbon nanotubes (CNTs) for high performance interconnects were developed. A small amount of CNTs (0.03 wt%) was dispersed into the NCAs/NCFs to increase the thermal conductivities and at the same time to decrease the coefficient of thermal expansion (CTE) for high thermo-mechanical reliability of the NCAs/NCFs interconnect joints. The thermal mechanical analyzer measurements showed that the CTE value of the 0.03 wt% CNTs filled NCAs/NCFs was significantly decreased. Current-voltage characterizations showed that the current carrying capabilities of the CNTs (0.03 wt%) filled NCAs/NCFs were increased 14% comparing to the unfilled NCAs/NCFs due to the more efficient thermal dissipation.

Surface treatment of MWCNT array and its polymer composites for TIM application

The multiwalled carbon nanotube (MWCNT) surface chemistry changes by microwave and UV/ozone treatments were studied and the treatment effects on the thermal conductivity of their polymer nanocomposites were investigated. Contact angle measurements, X-ray photoelectron spectroscopy (XPS) and Raman spectra were used for the CNT surface characterization. The surface functionalization and the CNT purification/annealing should be balanced for improving the thermal transport property of the MWCNT/polymer nanocomposites.