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The purpose of this paper is to investigate the influence of the properties of new compositions of fluxes for selective soldering on lead-free solder joints quality and microstructures as well as showing which flux properties are the most important.

The three different types of fluxes were tested, which differed in composition, solids content, amount and type of activators added. The selective soldering process was done with the use of lead-free solder SAC 305. The test boards had two coatings SnCu (HASL) or Au/Ni. Basic chemical and physical properties of fluxes were examined according to the relevant standards. Different types of components from the bulky ones, demanding more heat, to the smaller ones were used during the assembly process. AOI and X-ray analyses as well as cross-sections and SEM analyses were utilized to deeply assess the quality and microstructure of the investigated solder joints.

The results showed that information about density or static activity of flux is not enough for correct flux assessment. The dynamic activity of flux measured by wetting balance method is the best for this, especially in the case when there is short soldering time and heat transfer is hindered. The quality and the microstructure of lead-free solder joints are related not only with wetting properties of the flux used for soldering but also with other properties like solids content in a flux.

It is suggested that further studies are necessary for the confirmation of the practical application, especially of the reliability properties of the joints obtained with the use of the elaborated fluxes.

The results showed that type of flux (ORL or ROL) as well as minor changes in their dynamic activity and solids content might have significant influence on quality of solder joints and their microstructure. It was noted that selective soldering is demanding technique and optimization of soldering process for different type of components and fluxes is important.

Establishes a quantitative evaluation method on solder bridging in microsoldering using a printed wiring board with comb pattern conductors. Bridge tests were conducted by immersing the comb pattern board into a molten solder bath. The total length of solder bridge between conductors against the total length between conductors was measured as a measure of the occurrence of solder bridging. The occurrence of bridging depended on the number of immersions, flux activity including solid content, conductor spacing, solder bath temperature and solder composition. The increase in number of immersion enhanced bridging. The rosin flux without activators showed higher bridging than the activated flux. Sn‐37Pb solder showed lower bridging than Sn‐3.5Ag‐5Bi solder. Solder bridging was found to be closely correlated with wettability, therefore, the improvement of wettability could be effective to suppress solder bridging. The proposed method is believed to be suitable for the quantitative evaluation of solder bridging.

PCB manufacturers are switching from the use of RMA fluxes in their soldering and rework processes to low residue type (i.e., ‘no‐clean’) fluxes. Unfortunately, successful changeover is not simply a matter of substituting a no‐clean into an existing RMA process. Soldering process parameters must change, necessitating an understanding of the interplay between flux chemistry and heat delivery. Higher temperatures can result in an effective decrease in the concentration of the active fluxing agents. Also, data show a decrease in the inherent wetting force of a no‐clean flux with increasing temperature. These two factors reduce fluxing action below the rate of oxidation occurring at the solder connection and the soldering iron tip. These can lead to incomplete surface cleaning and inefficient heat transfer, resulting in poorly soldered connections. Lower solder joint defect rates are obtained with no‐clean solders and fluxes when soldering temperatures are reduced to a minimum.

The aim of this work is to investigate the decomposition behaviour of the activator species commonly used in the wave solder no-clean flux systems and to estimate the residue amount left after subjecting the samples to simulated wave soldering conditions.

Changes in the chemical structure of the activators were studied using Fourier transform infrared spectroscopy technique and were correlated to the exposure temperatures within the range of wave soldering process. The amount of residue left on the surface was estimated using standardized acid-base titration method as a function of temperature, time of exposure and the substrate material used.

The study shows that there is a possibility of anhydride-like species formation during the thermal treatment of fluxes containing weak organic acids (WOAs) as activators (succinic and DL-malic). The decomposition patterns of solder flux activators depend on their chemical nature, time of heat exposure and substrate materials. Evaporation of the residue from the surface of different materials (laminate with solder mask, copper surface or glass surface) was found to be more pronounced for succinic-based solutions at highest test temperatures than for adipic acid. Less left residue was found on the laminate surface with solder mask (∼5-20 per cent of initial amount at 350°C) and poorest acid evaporation was noted for glass substrates (∼15-90 per cent).

The findings are attributed to the chemistry of WOAs typically used as solder flux activators. The results show the importance WOA type in relation to its melting/boiling points and the impact on the residual amount of contamination left after soldering process.

The results show that the evaporation of the flux residues takes place only at significantly high temperatures and longer exposure times are needed compared to the temperature range used for the wave soldering process. The extended time of thermal treatment and careful choice of fluxing technology would ensure obtaining more climatically reliable product.

This paper outlines the composition of water soluble fluxes for the electronics industry and their methods of use when wave soldering and reflowing tinned coatings and solder pastes. Process optimisation is facilitated by the Taguchi method. Three types of cleaning machinery are evoked, with varying results. It is shown that the energy/time relationship is important to ensure adequate cleaning quality. A number of fallacious arguments are debunked. Methods of water purification and the problems of effluent treatment for all sizes of installation are addressed. Doubt is expressed as to the viability of closed‐circuit water recycling except for the largest installations or where exceptional conditions prevail. It is shown that water soluble fluxes and their subsequent aqueous removal are unlikely to make any significant contribution to the Greenhouse Effect. The overall cost of their use is substantially similar to that of rosin fluxes with CFC‐113 azeotropes at 1986 prices. Cleanliness control under production and laboratory conditions is discussed with reference to both ionic contamination testing, including its use for SMDs, and SIR analysis, especially at low voltages, including non‐destructive production SIR testing. Reliability of the assembled circuits is shown to be at least as good as that with more traditional soldering and cleaning methods, frequently better, and this is the case even for military and aerospace applications. The paper concludes that, now that quality water soluble solder pastes are available, this method is most likely to become the workhorse for the majority of electronics applications.

Recent developments in synthetic resin based non‐corrosive fluxes for soft soldering have coincided with completion of the work of the international flux standard committee. With the increasing usage of surface mounted components these special synthetic resin‐based, zero‐halide, low solids fluxes can be used to leave minimal residues after soldering, which without removal do not affect long‐term reliability of soldered assemblies. Similar chemistry has been applied to devise flux cored solders and solder pastes which also leave minimal, safe residues, thereby avoiding cleaning processes.

This study aims to synthesize polyethylene glycol (PEG)-rosin derivatives from rosin and PEG for the production of solid soldering fluxes. The PEG-rosin derivatives would be water soluble, and the resulting solid soldering fluxes would have reasonable wetting ability when combined with a low-halide-content activator.

This paper presents a synthetic process for PEG-rosin derivatives. The reaction conditions (including catalyst type, catalyst concentration, reaction temperature and PEG type) were optimized for the synthesis of PEG-rosin derivatives. The chemical and physical properties of PEG-rosin derivatives were characterized by Fourier transform infrared spectroscopy, carbon-13 nuclear magnetic resonance spectrometry, differential scanning calorimetry and gel permeation chromatography. The production and characteristics of water-soluble rosin fluxes (WSRFs) were studied according to the standards of the Japanese Industrial Standards (JIS) Committees.

WSRs were successfully synthesized from rosin and PEG using 2 per cent ZnO as a catalyst, with a 2:1 molar ratio of rosin:PEG at 250°C over 9 h. The resulting WSRs were completely soluble in water. As the PEG3000-rosin had the highest melting point (55.2°C), it was chosen for the preparation of the WSRFs. Activators such as succinic acid, glutaric acid, ethylamine hydrochloride and diethylamine hydrobromide were selected for use in the production of the fluxes. It was found that WSRF 09 and WSRF 04 gave the best performance with the lead-free Sn-0.7Cu solder alloy in terms of good solderability, low halide content (less than 1,500 ppm), high insulation resistance and low corrosion. These fluxes were applied to produce solder pastes with Sn-3.0Ag-0.5Cu alloy and they passed the performance tests as expected for solder paste.

Further studies are necessary on large-scale production and to compare the performance of these fluxes to those from conventional water-soluble fluxes currently available in the market. Application of these fluxes on low-temperature solder alloys such as SnZn and SnBi (Ren et al., 2016) worth further study.

The classification of flux systems according to the JIS 3283 standard does not specify PEG-rosin derivatives in the flux; nevertheless, ranking of the flux systems based on the halide content and corrosion properties of activators would be useful information when selecting flux systems for electronics soldering in water-washable applications. The application of these fluxes in solder paste gave very promising results and is worth investigating into more detail, as well as field test.

No‐clean flux printed board appraisal tests were conducted with all materials used in the production process. Metallic growths during environmental testing revealed that there was incompatibility between some materials used. Initial tests with two solder resists and several fluxes showed that one non solder resisted board, soldered using a synthetically activated (SA) flux, had surface insulation resistance (SIR) two decades higher than those using low solids flux (LSF) or other SAs. For boards with solder resist, the SIR of those soldered using LSFs was higher, however, than those using SA fluxes. SIR dependence on temperature and humidity was investigated. Results demonstrated that the dominant factor to determine the SIR of a no‐clean board was the characteristics of the board substrate finish. SIR changes with condensation were logged and found to be significant for solder resist finishes. Tests proved that reducing the contamination levels under and on top of the solder resist, by using hot de‐ionised water rinsing, enabled the calculated minimum SIR level to be achieved for spray fluxed boards and minimised the possibility of metallic growth. Visual examination proved to be at least as important as SIR testing. No‐clean processes were appraised using sequential environmental conditions with differing SIR pass levels. As a result of this appraisal a maximum ionic contamination level of 0·5 μg/cm2 NaCl equivalent and Dl water rinses, before and after solder resist added, will be introduced. Ionic contamination tests indicated that contamination levels reduced with elapsed time, probably due to ionic molecules locking more firmly into the board surface structure. A novel method for SIR measurements at any voltage, developed by the author, is described. It is hoped that this paper will further the understanding of no‐clean flux issues and highlight potential solutions and pitfalls.

The purpose of this paper is to investigate the wettability and intermetallic (IMC) layer formation of Sn-3.0Ag-0.5Cu (SAC305)/CNT/Cu solder joint according to the formulation of solder paste because of different types of fluxes.

Solder pastes were prepared by mixing SAC305 solder powder with different flux and different wt.% of carbon nanotube (CNT). Fourier transform infrared spectroscopy was used to identify functional groups from different fluxes of as-formulated solder paste. The solder pastes were then subjected to stencil printing and reflow process. Solderability was investigated via contact angle analysis and the thickness of cross-sectionally intermetallic layer.

It was found that different functional groups from different fluxes showed different physical behaviour, indicated by contact angle value and IMC layer thickness. “Aromatic contain” functional group lowering the contact angle while non-aromatic contain functional group lowering the thickness of IMC layer. The higher the CNT wt.%, the lower the contact angle and IMC layer thickness, regardless of different fluxes. Relationship between contact angle and IMC layer thickness is found to have distinguished region because of different fluxes. Thus it may be used as guidance in flux selection for solder paste formulation.

However, detail composition of the fluxes was not further explored for the scope of this paper.

The quality of solder joint of SAC305/CNT/Cu system, as indicated by contact angle and the thickness of IMC layer formation, depends on existence of functional group of the fluxes.

This paper aims to investigate the effect different fluxes have on the mechanical properties of lead-free solders, specifically Sn-Zn-Bi solder alloy. The solder billets were soldered in between copper substrates and flux was applied. The mechanical tests carried out on the solder alloys were tensile and shear tests. They were experimented on with different fluxes, namely, water-soluble (paste), rosin mildly activated (RMA) and insoluble (RMA) flux. From these experiments, the ultimate tensile strength, shear strength, elongation, yield stress, Young’s modulus and the stress-strain curve are derived. The results showed that solder billets that were soldered onto copper substrates with water-soluble flux yielded the highest ultimate tensile strength and shear strength values of 9.9961 MPa and 118.836 MPa, respectively. Billets soldered using RMA flux had the highest values of elongation and Young’s modulus, 0.306 mm and 50,257.295 MPa, respectively. However, on viewing the failure of all the specimens under an optical microscope and scanning electron microscope (SEM), specimens soldered using water-soluble flux possessed the least deformities, depicting their higher level of mechanical properties, entailing their strength and ductility, deeming them as the most suitable flux for microelectronic applications.

The solder billets were soldered in between copper substrates and flux was applied. The mechanical tests carried out on the solder alloys were tensile and shear tests. They were experimented on with different fluxes, namely, water-soluble (paste), RMA and insoluble flux (RMA) flux. From these experiments, the ultimate tensile strength, shear strength, elongation, yield stress, Young’s modulus and the stress-strain curve are derived.

The results showed that solder billets that were soldered onto copper substrates with water-soluble flux yielded the highest ultimate tensile strength and shear strength values of 9.9961 MPa and 118.836 MPa, respectively.

This paper demonstrated that water-soluble fluxes gave the better strength and were most suitable for microelectronics applications.