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This paper aimed to investigate the effects of nano-copper particles on the melting behaviors, wettability and defect formation mechanism of the Sn58Bi composite solder pastes.

In this paper, the mechanical stirring method was used to get the nano-composite solder pastes.

Experimental results indicated that the addition of 3 wt.% (weight percentage) 50 nm copper particles showed limited effects on the melting behaviors of the Sn58Bi composite solder paste. The spreading rate of the Sn58Bi composite solder paste showed a decreasing trend with the increase of the weight percentage of 50 nm copper particles from 0 to 3 wt.%. With the addition of copper particles of diameters 50 nm, 500 nm or 6.5 μm into the Sn58Bi solder paste, the porosities of the three types of solder pastes showed a similar trend. The porosity increased with the increase of the weight percentage of copper particles. Based on the experimental results, a model of the void formation mechanism was proposed. During reflow, the copper particles reacted with Sn in the matrix and formed intermetallic compounds, which gathered around the voids produced by the volatilization of flux. The exclusion of the voids was suppressed and eventually led to the formation of defects.

This study provides an optimized material for the second and third level packaging. A model of the void formation mechanism was proposed.

The purpose of this paper is to investigate risk dimensions affecting food risk perceptions and to develop effective risk communication strategies based on their risk perceptions dimensions. The reason for writing this paper is that applying single risk communication strategy for public often fails because food risks are systemic risks and public perceptions toward them consist of multiple dimensions. Launching an effective risk communication need to investigate the perception dimensions of the target audience.

A total of 2,673 parents of 3-14-year-old children from the rural area of Sichuan province in China were chosen as target audience. Based on the survey conducted about parents’ food risk perceptions, this study used factor-cluster analysis method to segment parents to sub-clusters with significantly different risk perception dimensions. Parents’ representative demographic characteristics within each cluster were further identified through cross-tabs analysis with χ² tests.

All the parents could be segmented into four sub-clusters, namely, sensitive parents, dependent parents, familiarity-oriented parents and institutional distrust parents, according to their risk perception difference on five dimensions. A series of risk communication strategies were specifically designed for each cluster based on their risk perception features as well as demographic characteristics.

The insight derived from this study described a deeper image of public risk perceptions and provided suggestions for risk communication launchers to pinpoint the risk perception as well as perception dimensions of the target audience and accordingly develop effective risk communication strategies.