AT-265

Solder/Cu joints are important components responsible for interconnection in microelectronics. Construction of the solder/Cu joints through liquid/solid (L/S) reactions accompanies the formation of the Cu-Sn intermetallic compounds (IMCs) at the joint interface. The Cu6Sn5 IMC exhibits remarkable distinctions in thickness and morphology upon increasing the L/S reaction time. Effects of the initial characteristics of thickness and morphology on the growth kinetics of Cu6Sn5 during subsequent isothermal aging were investigated. SAC305 solder was reflowed on a Cu electroplated layer at 265 °C for 1 to 60 min to produce the Cu6Sn5 IMC with different thickness and morphology at the SAC305/Cu interface. The as-fabricated SAC305/Cu joint samples were aged at 200 °C for 72 to 360 h to investigate the growth kinetics of Cu6Sn5. The results show that the initial characteristics of thickness and morphology significantly influenced the growth kinetics of Cu6Sn5 during the subsequent solid/solid (S/S) reaction. A prolonged L/S reaction time of 60 min (L/S-60) produced a scallop-type Cu6Sn5 IMC with a larger grain size and a thicker thickness, which reduced the quantity of fast diffusion path (grain boundary) and the magnitude of concentration gradient, thus slowing down the growth rate of Cu6Sn5. According to the growth kinetics analysis, the growth rate constant of Cu6Sn5 could be remarkably reduced to 0.151 µm/h0.5 for the L/S-60 sample, representing a significant reduction of 70 % compared to that of the L/S-1 sample (0.508 µm/h0.5 for L/S reaction time of 1 min).

Ultraviolet C (UVC) radiation is a widely used technology for the disinfection of surfaces, air flows, water and other liquids. Although extensive research has been conducted on the UV tolerance of bacteriophages used as surrogates for waterborne viruses, limited information is available on phages relevant to food processing. Phages of dairy starters may reach high numbers in dairy facilities and cause fermentation failure with great economic losses for the dairy industry. Here, the UV tolerance of virulent phages, belonging to the 936-group (Skunavirus) of Lactococcus lactis subsp. diacetylactis F7/2, was assessed, employing both host infectivity loss and qPCR assays. A highly heat-tolerant phage (P680) and a less heat-tolerant phage (P008) were exposed to UV radiation at 265 nm (UVC), 285 nm (UVB) and 365 nm (UVA), respectively, in an aqueous suspension, using UV Light-Emitting-Diodes (LEDs) in a static set-up. UVC at 265 nm achieved the highest total inactivation, leading to a 4 log10 reduction of the phage titer at a UV dose of 327 and 164 mJ/cm2 for P680 and P008, respectively. UVB at 285 nm achieved similar inactivation levels, while UVA at 365 nm did not cause major reductions. Phages were also suspended in yoghurt serum of pH 5.5 and pH 7.0 and exposed to UVC radiation at 265 nm. The heat-tolerant phage P680 was more UV tolerant for all wavelengths, matrices and pH values tested. A higher aggregation degree together with less DNA damage was observed for both phages at pH 5.5, especially for phage P680, indicating a UV light-shielding effect. Interestingly, there were indications of some phage survivors exhibiting higher UV tolerance on re-exposure, pointing out a need for further investigation. Our results show that UV LEDs emitting at 265 nm and 285 nm are efficient in reducing the phage population significantly, but also underline that 936-type phages are relatively UV resistant. A further understanding of the main factors influencing UV efficiency could enable future use of the UV technology as an alternative or complement to thermal treatment for phage inactivation.

The risk of sepsis through bacterial transmission is one of the most serious problems in platelet transfusion. In processing platelet concentrates (PCs), several methods have been put into practice to minimize the risk of bacterial transmission, such as stringent monitoring by cultivation assays and inactivation treatment by photoirradiation with or without chemical agents. As another potential option, we applied a light-emitting diode (LED) with a peak emission wavelength of 265 nm, which has been shown to be effective for water, to disinfect PCs. In a bench-scale UV-LED exposure setup, a 10-min irradiation, corresponding to an average fluence of 9.2 mJ/cm2, resulted in >2.0 log, 1.0 log, and 0.6 log inactivation (mean, n = 6) of Escherichia coli, Staphylococcus aureus, and Bacillus cereus, respectively, in non-diluted plasma PCs. After a 30-min exposure, platelet counts decreased slightly (18 ± 7%: mean ± SD, n = 7); however, platelet surface expressions of CD42b, CD61, CD62P, and PAC-1 binding did not change significantly (P>0.005), and agonist-induced aggregation and adhesion/aggregation under flow conditions were well maintained. Our findings indicated that the 265 nm UV-LED has high potential as a novel disinfection method to ensure the microbial safety of platelet transfusion.