Silica particles are used as a filler material in electronic underfills to reduce coefficient of thermal expansion of the underfill-epoxy matrix. In traditional underfills, the size of silica particles is in the micrometer range. Reduction in particle sizes into the nanometer range has the potential of attaining higher volume fraction particle loading in the underfills and greater control over underfill properties for higher reliability applications. Presently, no-flow underfills have very low or no filler content because micron-size filler particles hinder solder joint formation. Nano-silica underfills have the potential of attaining higher filler loading in no-flow underfills without hindering solder interconnect formation [9], [16].In this paper, property prediction models based on representative volume element (RVE) and modified random spatial adsortion have been developed. The models can be used for development of nano-silica underfills with desirable thermo-mechanical properties. Temperature dependent thermo-mechanical properties of nano-underfills have been evaluated and correlated with models in a temperature range of 175 C to +150 C. Properties investigated include, temperature dependent stress-strain, creep and stress relaxation behavior. Nano-underfills on 63Sn37Pb eutectic and 95.5Sn3.5Ag1.0Cu leadfree flip-chip devices have been subjected to thermal shock tests in the range of 55 C to 125 C and 55 C to 150 C, respectively. The trade-offs between using nano-fillers instead of micron-fillers on thermo-mechanical properties and reliability has been benchmarked.Index Terms-Coefficient of thermal expansion (CTE), representative volume element (RVE), system in package (SIP).
Vertically Aligned Carbon Nanotube arrays (also termed as VACNTs or CNT forest) have recently found to be transformable to a reflective mirror from a naturally black absorber. The feature of improved reflectance can be attained by the controllable tip bending process using the bottom surface of a rotated cylindrical tool (the process called micromechanical bending (M2B)). In this paper, the polarized light reflectance of bent and compacted region of the CNT forest using M2B method has been investigated. We observed that reflectance from the processed CNT zone was highly dependent on the angle of incidence and polarization state of the incident laser. For the first time, the refractive index of the tip bent CNT forests by M2B method was investigated and found to be in a range of ~1.8.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.