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Residues associated with soldering operations are common throughout the electronics manufacturing industry. Prevention is necessitated by MIL specs which require soldered assemblies to be free of all residues. Because of the large number of variables which contribute to residue formation, residues frequently appear under seemingly constant conditions, and detailed understanding of the materials and processes involved is needed for corrective action implementation. This paper presents the history of an investigation of white residue on solder masked printed wiring assemblies. The residue was determined to be flux related by experimentation and spectroscopic chemical analysis. Process modification testing was performed to evaluate the roles of flux identity, preheater temperatures and several cleaning process variables. Assemblies were subjected to humidity and temperature cycling, including periodic examination and electrical testing. Additionally, information learned during this investigation about a number of residue causes and cures is summarised.

Visible surface residues, commonly referred to as white residues, on soldered printed circuit assemblies are a very common but intermittent and unpredictable problem. Such residues, which are insoluble in normal solvents, are generally a rejectable condition. The chemistry of the deposition of white residues is complex; the deposits themselves are of a number of types and origins, and their incidence is associated with both materials and process parameters. This paper attempts to identify the different causes of the problem and suggest ways in which avoidance or removal is possible.

The purpose of this paper is to investigate the decomposition behavior of binary mixtures of organic activators commonly used in the no-clean wave flux systems upon their exposure to thermal treatments simulating wave soldering temperatures. The binary blends of activators were studied at varying ratios between the components.

Differential scanning calorimetry and thermogravimetric analysis were used to study the characteristics of weak organic acid (WOA) mixtures degradation as a function of temperature. The amount of residue left on the surface after the heat treatments was estimated by gravimetric measurements as a function of binary mixture type, temperature and exposure time. Ion chromatography analysis was used for understanding the relative difference between decomposition of activators in binary blends. The aggressivity of the left residue was assessed using the acidity indication gel test, and effect on reliability was investigated by DC leakage current measurement performed under varying humidity and potential bias conditions.

The results show that the typical range of temperatures experienced by electronics during the wave soldering process is not sufficient for the removal of significant activator amounts. If the residues contain binary mixture of WOAs, the final ratio between the components, the residue level and the corrosive effects depend on the relative decomposition behavior of individual components. Among the WOA investigated under the conventional wave soldering temperature, the evaporation and removal of succinic acid is more dominant compared to adipic and glutaric acids.

The findings are attributed to the chemistry of WOAs typically used as flux activators for wave soldering purposes. The results show the importance of controlling the WOA content and ratio between activating components in a flux formulation in relation to its tendencies for evaporation during soldering and the impact of its residues on electronics reliability.

The results show that the significant levels of flux residues can only be removed at significantly higher temperatures and longer exposure times compared to the conventional temperature range used for the wave soldering process. The potential corrosion issues related to insufficient flux residues removal will be determined by the residue amount, its composition and ratio between organic components. The proper time of thermal treatment and careful choice of fluxing formulation could ensure more climatically reliable product.

Agricultural food residues (agro-residues) receive low economic returns and experience disposal problems. The food production and processing is often not configured to supply agro-residues for production of bioenergy needed in food processing. The feasibility of utilising agro-residues through advances in postharvest technology for sustainable bioenergy conversion is reviewed. The paper aims to discuss this issue.

Agro-residues from maize, sugarcane and potatoes in five African countries were assessed from secondary data to identify suitable conversion technologies, energy products and configurations of bioenergy plants for applications in postharvest food processing.

Strategic alignment of postharvest technology to bioenergy production systems is vital to advancing both food production and bioenergy that benefit rural communities in Africa. High economic returns are possible when the bioenergy plants are either annexure to existing agro-processing operations or operate as a biorefinery.

Assessment of energy self-sufficiency of food production and processing systems is required.

Agro-residues for bioenergy production require investments in infrastructure for storage, transportation and processing of the residues, and development of new risk management techniques.

The rural communities will be energy secure resulting in food security through reduced postharvest losses and increased agricultural productivity.

The study stimulates innovative thinking in establishing sustainable bioenergy systems for food processes.

The purpose of this paper was to analyse typical printed circuit board assemblies (PCBAs) processed by reflow, wave or selective wave soldering for typical levels of process-related residues, resulting from a specific or combination of soldering processes. Typical solder flux residue distribution pattern, composition and concentration are profiled and reported. The effect of such contaminants on conformal coating was tested.

Presence of localized flux residues was visualized using a commercial residue reliability assessment testing gel test and chemical structure was identified by Fourier transform infrared spectroscopy, while the concentration was measured using ion chromatography, and the electrical properties of the extracts were determined by measuring the leak current using a twin platinum electrode set-up. Localized extraction of residue was carried out using a commercial critical contamination control extraction system.

Results clearly show that the amount and distribution of flux residues are a function of the soldering process, and the level can be reduced by an appropriate cleaning. Selective soldering process generates significantly higher levels of residues compared to the wave and reflow process. For conformal coated PCBAs, the contamination levels generated from the tested wave and selective soldering process are found to be enough to generate blisters under exposure to high humidity levels.

Although it is generally known that different soldering processes can introduce contamination on the PCBA surface, compromising its cleanliness, no systematic work is reported investigating the relative levels of residue introduced by various soldering processes and its effect on corrosion reliability.

For many years the analysis of contaminant residues on PWB surfaces has been of major importance to the industry. While the identification of residues left on metallic surfaces has proven to be relatively straightforward, the analysis of organic contamination of similar composition to that of the underlying board surface has not been as successful. Through the use of modern XPS instrumentation, the non‐ionic component of water soluble flux has been identified and differentiated from the chemically similar FR‐4 and soldermask substrates. This paper presents the XPS results for a series of experiments aimed at determining the location and relative concentration of water soluble flux residues on standard surface insulation resistance (SIR) comb patterns. The data show that the water soluble flux residue is not present as a uniform coating on the board surface but appears in localised sites in high concentrations while being absent in other locations. Through more aggressive cleaning procedures the sites of high residue concentration can be significantly reduced.

The purpose of this paper is to present a case report involving environmental performance analysis of a small Brazilian business from the foundry industry.

An environmental performance indicator was developed (I_epa) which is calculated taking into consideration the weighting of potential environmental impacts of each residue/sub product generated, the relative spatial dispersion which each residue/sub product can reach, and the adequacy evaluation of final allocation accomplished by the company for each residue/sub product.

Despite the evidence that the corporation do not conduct washing of gases emitted from the chimney of the foundry furnace, which consists an environmentally inadequate attitude, the result of I_epa=97.50 percent was obtained. This favorable result is due to the adequate allocation given to residues generated in greater volume in the process, the molding sand. This sand is addressed to an industrial landfill, which is an environmentally adequate practice and approved by competent environmental authorities.

The method used can be applied to measure the environmental impact generated by any business of the foundry sector industry.

The originality of the work is in the developed method, which takes into account: the potential impact of each residue/sub product generated, the amount of each residue/sub product generated in a given time period, the dispersion that each residue/sub product can attain, and the evaluation of eventual allocation of each residue/sub product.

Pesticide residue is a stubborn problem affecting the quality and safety of agricultural products in China, and has not yet been fundamentally resolved. The purpose of this paper is to study farmers' perception of pesticide residues, as well as the main factors affecting their perception from the viewpoint of farmers. Additionally, this research attempts to explore the basic characteristics of pesticide residues arising in the process of producing agricultural products under the prevailing policy background, so as to provide decision‐making references for the Chinese government to deepen the security management system of agricultural products.

The structural equation model (SEM) is an analytical tool for the observation and treatment of latent variables that are difficult to observe directly, and for the consideration of inevitable errors. This paper investigates the main factors affecting farmers' perception of pesticide residues in the investigated regions based on the SEM and samples of 241 farmers in six counties (cities and regions) of three districts in the Jiangsu Province of China.

According to the research, regional difference, farmers' gender, age, years of education, pesticide training and their own demand for safe agricultural products had different influences on their perception of pesticide residues. Additionally, it was difficult to measure the influence of family characteristics on farmers' perception of pesticide residues. Although the present paper only shows a preliminary study, its conclusion provides a reference value for the Chinese government to deepen the reform of the quality and safety regulatory system of agricultural products.

There are many similar studies in overseas countries, but the application of SEM in the study of the main factors affecting farmers' perception of pesticide residues has not been completely reported previously in domestic literatures. The research assumption of this paper has practically verified that corresponding research conclusions of foreign scholars in this field have universality in China.

Powder bed fusion (PBF) additive manufacturing (AM) has facilitated the production of medical devices with intricate geometries and patient-matched features. The medical industry especially has leveraged complex geometries for orthopedic applications. However, these geometries increase the difficulty of manufacturing residue removal. Furthermore, PBF-specific methods for residue removal and quantification have not been developed yet. This study aims to assess the use of a novel challenge assembly to evaluate PBF residue removal protocols.

A novel modular PBF challenge assembly was evaluated for its ability to resolve differences in the residue removal techniques. Several metrics were adapted from consensus standards and applied to evaluate their suitability. Though the challenge assembly can incorporate multiple complex geometries and reticulated structures, this study used the test case of regular lattice structures and two generic residue removal protocols (RRPs).

The challenge assembly successfully represented increasingly complex residue removal scenarios, showing increasing amounts of residue remaining in parts of increasing density. Simultaneous examination of multiple geometries with different residue removal difficulties can be used to design production processes. Indirect estimates of extracted residue provided some information on residue remaining. However, they were not sufficient to evaluate the part because of the high variability and uncertainty. Additional metrics proved necessary to corroborate the results during a verification phase. A carefully selected panel of metrics could provide adequate information to validate a process.

This study evaluated and demonstrated a framework to assess RRPs for complex geometries. It showed that the results of single indirect metrics such as extracted residues may provide ambiguous results across a range of parts. PBF-specific metrics for residue removal and quantification would greatly improve repeatability and certainty.

For soldering, flux is essential because it enables the wetting of the molten solder. Fluxless soldering, i.e. residue-free soldering with the aid of gaseous activators, has been known for many years, but is only well established in the field of opto- and microwave electronics where the solder is applied as preform. In high-volume SMD applications where solder paste is printed, this technology is rarely used until now. The reducing effect of a gaseous activator like formic acid vapor on certain solder alloys is known in practice. However, the corresponding reactions which occur under soldering conditions in nitrogen atmosphere have so far not been systematically investigated for different solder alloys. This study aims to analyze the different chemical reaction channels which occur on the surface of different solders, i.e. catalytical dissociation of formic acid on the pure or oxidized metal surface and the formation and evaporation of metal formates. Based on this analysis, a residue-free solder process under formic acid is developed for solder paste applications.

In this paper, different solder alloys (SnAgCu, SnPb, BiSn, In) were analyzed with thermal gravimetric analysis (TGA) under formic acid flow. Details on mass change depending on the soldering temperature are presented. Activation temperatures are estimated and correlated to the soldering processes. Based on the analysis, fluxless solder pastes and suitable soldering processes are developed and presented. Major paste properties such as printability are compared to a commercial flux solder paste. High-power flip chip LEDs which can be assembled directly on a printed circuit board are used to demonstrate the fluxless soldering. Likewise, the soldering results of standard paste and fluxless paste systems after a reflow process are evaluated and compared.

The experimental results show that TGA is an efficient way to gain deeper understanding of the redox processes which occur under formic acid activation, i.e. the formation of metal formates and their evaporation and dissociation. It is possible to solder residue-free not only with preforms but also with a fluxless solder paste. The resulting solder joints have the same quality as those for standard solder paste in terms of voids detected by X-ray and mechanical shear strength.

In the fluxless soldering process, the reduction of oxide layers, and therefore the wetting of the solder spheres, is enabled by gaseous formic acid. After the soldering process, no cleaning process is necessary because no corrosive residues are left on the circuit boards and components. Therefore, soldering using solder paste without aggressive chemical ingredients has a high market potential. Expensive preforms could be replaced by paste dispensing or paste printing.