Quantitative Assessment of Water Contaminants in the Rupsha River of Khulna Region for Irrigation Usage

Water samples were collected from the Rupsha river of Khulna region to determine ionic contamination for irrigation purpose. The chemical analyses included pH, EC, TDS and ions. pH values of water samples were slightly alkaline in nature. Samples were rated as fresh water based on TDS values. Samples were high salinity and low alkalinity hazards expressing C3S1. Regarding SAR and SSP values, samples were excellent and good classes, respectively. Samples were free from RSC and were very hard class. Regarding PI values, samples were under class-II implying 75% maximum soil permeability. Ca, Mg, Na, Cu, Ni, Zn, HCO3, SO4 and PO4 levels in samples were within safe limit. Cd, Cr and Cl ions in water samples were above the permissible limit and were treated as water contaminants for irrigation. From the present findings, it is noted that the detected ions as water contaminants should be considered for irrigation usage toward food safety. J. Environ. Sci. & Natural Resources, 11(1-2): 145-151 2018

Impact of titanium dioxide nanoparticles on purification and contamination of nematic liquid crystals

We have investigated the impact of titanium dioxide nanoparticles on the ionic contamination of liquid crystals. Nematic liquid crystals with high and low initial ionic contamination have been examined. It has been shown that titanium dioxide nanoparticles reduced the ion density of liquid crystals with high initial ionic contamination from 134.5 × 1012 cm−3 to 63.2 × 1012 cm−3. In the case of liquid crystals with low initial ionic contamination, the nanoparticles led to an insignificant increase of ion density from 19.8 × 1012 cm−3 to 25.7 × 1012 cm−3.

Case Study—Failure Analysis of a Printed Circuit Board Latent Failure and Resulting Implication of Weaknesses in Panel Coupons and Lot DPA

Multiple, independent, system level test failures that occurred around the same time were traced back to a short circuit on the same type of printed circuit board (PCB). The PCBs were removed from the application and sent to the authors' lab for analysis. This paper reviews the analysis techniques and results that led to the failure mechanism being identified. The discussion focuses on steps taken to exonerate the authors' lab and processes as possible sources of contamination. Additional investigation that leads to the conclusion that the issue is systemic is also covered. The paper then focuses on the containment effort as well as root cause identification at the manufacturers. It was concluded that the failure mechanism causing the short circuit in the failed PCB is due to ionic contamination trapped inside the PCB. The normal chemistry required to process the plated through holes contaminated the voids/fractures created by drilling process.

Solderability and Reliability Evolution of No-Clean Solder Fluxes For Selective Soldering

Flux consumption for wave soldering tends to decrease, mainly due to its gradual replacement by reflow soldering methods (i.e. pin-in-paste) in many electronics applications. However, in several cases, wave soldering still remains a must, with an increasing share of “selective” soldering processes, either using wave frames with dedicated apertures or solder fountains. Such processes are more challenging for the fluxes in terms of reliability under operation, since some chemistries remaining on the printed circuit boards after soldering may promote corrosion. Thus, flux manufacturers had to adapt their formulations to minimize such issues while keeping an efficient activation level, with several types of alloys (tin-lead, tin-silver-copper and low/no-silver) and associated with the numerous types of finishes encountered. The paper will cover the types of flux used in the electronic industry according to their chemistry and activation level (rosin-based, halides, alcohol-based or water-based flux…), and their characteristics with reference to standards. The limits of current standards will be discussed in regards to the last generation solder fluxes. Then, the development of two low-residue new generation fluxes, an alcohol-based flux and a true VOC-free flux, will be described, according to requirements: the lab tests results (surface tension, spread tests, wettability tests…) will be presented and discussed. Reliability will be especially investigated through surface insulation resistance, electro-chemical migration test, ionic contamination as well as Bono tests to determine the candidates able to provide high processability combined with chemical inertness of residues. Finally, the performance of flux will be assessed through customer tests, involving several types of boards, finishes and different solder alloys and wave equipment.