Search results

The purpose of the paper is to develop a methodology to characterize the rheological behaviour of macroscopic non-Brownian suspensions, like solder paste, based on microstructural evolution.

A structure-based kinetics model, whose parameters are derived analytically based on assumptions valid for any macroscopic suspension, is developed to describe the rheological behaviour of a given fluid. The values of the parameters are then determined based on experiments conducted at a constant shear rate. The parameter values, obtained from the model, are then adjusted using an optimization algorithm using the mean deviation from experiments as the cost function to replicate the measured rheology. A commercially available solder paste is used as the test fluid for the proposed method.

The initial parameter values obtained through the analytical model indicates a structural breakdown that is much slower than observations. But optimizing the parameter values, especially the ones associated with the structural breakdown, replicates the thixotropic behaviour of the solder paste reasonably well, but it fails to capture the structure build-up during the three interval thixotropy test.

The structural kinetics model tends to under-predict the structure build-up rate.

This study details a more realistic prediction of the rheological behaviour of macroscopic suspensions like solder paste, thermal interface materials and other functional materials. The proposed model can be used to characterize different solder pastes and other functional fluids based on the structure build-up and breakdown rates. The model can also be used as the viscosity definitions in numerical simulations instead of simpler models like Carreau–Yasuda and cross-viscosity models.

The rheological description of the solder paste is critical in determining its validity for a given application. The methodology described in the paper provides a better description of thixotropy without relying on the existing rheological measurements or the behaviour predicted by a standard power-law model. The proposed model can also provide transient viscosity predictions when shear rates vary in time.

Discusses the various methods that are used for measuring the viscosity of paints and inks in the laboratory environment and suggests what equipment is most suitable for different applications. Identifies the most common sources of errors in making measurements and emphasizes the importance of calibration in obtaining accurate and reproducible results.

The rheological properties of coating suspensions containing a blend of clay and CaCO3 as a pigment have been evaluated at 22°C, using a rheometer with shear rates from 0.5 to 100rpm. The state of dispersion of the pigment, the structure viscosity of the suspension as a result of pigment‐pigment or pigment‐binder interactions, and its behaviour by changing the solid content and ionic strength, were limited from the examination of the flow curves. The flow parameters for each suspension were calculated. The results showed that changes in solid content and ionic strength by the addition of divalent simple electrolyte (CaCl2) and pH level have a more profound effect on the flow parameters than that obtained by the addition of monovalent simple electrolyte (NaCl) or polyelectrolyte soluble polymers (CMC) with different degrees of substitution. The type of acid used to adjust the pH of the suspension also has a great influence on the flow parameters.

This paper presents a technique for mapping the modelling of manufacturing processes, in which process maps are used to represent information on the models and modelling technique (including assumptions used), process and equipment parameters, physical sub‐processes, process variables, and the process performance in terms of quality and/or defects. The mapping approach uses the top‐down methodology, in which any manufacturing process can be represented in a structured, multi‐layered manner, with each layer representing a different level of the modelling spectrum. This structure is designed to provide a clear overview of the process and sub‐processes, and their interactions, while the finer details of the modelling process are still presented at the lower levels of the map. This mapping approach is illustrated with the modelling of the Printing of Solder Paste for the reflow soldering of SMT devices. This case study shows how the mapping process can be used to identify the key research issues, specify the experimental work required, and also identify the analytical modelling techniques which are appropriate for each process (and sub‐process).

A measurement method has been developed to reveal the viscosity change of solder pastes during stencil printing. This paper aimed to investigate thixotropic behaviour, the viscosity change of a lead-free solder paste (Type 4).

The viscosity change of the solder paste during stencil printing cycles was characterised in such a way that the time-gap between the printing cycles was modelled with a rest period between every rheological measurement. This period was set as 15, 30 and 60 s during the research. The Cross model was fitted to the measurement results, and the η₀ parameter was used to characterise the viscosity change. The number of printing cycles necessary for reaching a stationary state in viscosity was determined for various rest periods.

It was found that the decrease in zero-shear viscosity is significant (25 per cent) in the first cycles, and it starts to become stationary at the sixth-seventh cycles. This means a printing process can provide the appropriate deposits only after the 7th cycle with the investigated Type 4 solder paste.

Time-dependent rheological behaviour of solder pastes was studied in the literature, but only the viscosity change over continuous time at constant shear rates was examined. The time-gap between stencil printing cycles was not considered, and thixotropic behaviour of solder pastes was also neglected. Therefore, the authors developed a measurement set which is able to model the effect of time-gap between printing cycles on the viscosity change of solder pastes.

The aim of this paper is to characterize the rheological properties of the flux media exposed to different levels of solicitation and to determine its influence on the rheology of the solder paste. The data obtained experimentally are fundamental for the development of numerical models that allow the simulation of the printing process of printed circuit boards (PCB).

Rheological tests were performed using the Malvern rheometer Bohlin CVO. These experiments consist of the analysis of the viscosity, yield stress, thixotropy, elastic and viscous properties through oscillatory tests and the capacity to recover using a creep-recovery experiment. The results obtained from this rheological analysis are compared with the rheological properties of the solder paste F620.

The results have shown that the flux is viscoelastic in nature and shear thinning. The viscosity does not decrease with increasing solicitations, except in the case where the flow is withdrawn directly from the bottle. Even if the solder paste shows a thixotropic behavior, this is not the case of the flux, meaning that this property is given by the metal particles. Furthermore, the oscillatory tests proved that the flux presents a dominant solid-like behavior, higher than the solder paste, meaning that the cohesive/tacky behavior of the solder paste is given by the flux.

To complement this work, printing tests are required.

This work demonstrates the importance of the rheological characterization of the flux in order to understand its influence in the solder paste performance during the stencil printing process.

The purpose of this paper is to develop a quality control tool based on rheological test methods for solder paste and flux media.

The rheological characterisation of solder pastes and flux media was carried out through the creep‐recovery, thixotropy and viscosity test methods. A rheometer with a parallel plate measuring geometry of 40 mm diameter and a gap height of 1 mm was used to characterise the paste and associated flux media.

The results from the study showed that the creep‐recovery test can be used to study the deformation and recovery of the pastes, which can be used to understand the slump behaviour in solder pastes. In addition, the results from the thixotropic and viscosity test were unsuccessful in determining the differences in the rheological flow behaviour in the solder pastes and the flux medium samples.

More extensive rheological and printing testing is needed in order to correlate the findings from this study with the printing performance of the pastes.

The rheological test method presented in the paper will provide important information for research and development, quality control and production staff to facilitate the manufacture of solder pastes and flux media.

The paper explains how the rheological test can be used as a quality control tool to identify the suitability of a developmental solder paste and flux media used for the printing process.

The purpose of this paper is to investigate the effect of different viscosity models (Cross and Al-Ma’aiteh) and different printing speeds on the numerical results (e.g. pressure over stencil) of a numerical model regarding stencil printing.

A finite volume model was established for describing the printing process. Two types of viscosity models for non-Newtonian fluid properties were compared. The Cross model was fitted to the measurement results in the initial state of a lead-free solder paste, and the parameters of a Al-Ma’aiteh material model were fitted in the stabilised state of the same paste. Four different printing speeds were also investigated from 20 to 200 mm/s.

Noteworthy differences were found in the pressure between utilising the Cross model and the Al-Ma’aiteh viscosity model. The difference in pressure reached 33-34% for both printing speeds of 20 and 70 mm/s and reached 31% and 27% for the printing speed of 120 and 200 mm/s. The variation in the difference was explained by the increase in the rates of shear by increasing printing speeds.

Parameters of viscosity model should be determined for the stabilised state of the solder paste. Neglecting the thixotropic paste nature in the modelling of printing can cause a calculation error of even approximately 30%. By using the Al-Ma’aiteh viscosity model over the stabilised state of solder pastes can provide more accurate results in the modelling of printing, which is necessary for the effective optimisation of this process, and for eliminating soldering failures in highly integrated electronic devices.

A series of articles dealing, in as simple a way as possible, with the basic facts of lubrication, lubricants, their selection and prescription, specification, application, and testing. This series is primarily intended for students, engineering personnel who may be unfamiliar with certain aspects and others who, one way or another, are interested in this important subject. Part One in our March 1965 Issue dealt with Friction, Lubrication and Wear. Part Two in July dealt with Mineral Oils and their Additives. Part Three, in September and October dealt with Lubricating Greases. Part Four in December and January covered the Purpose and Significance of Lubricant Tests.

The purpose of this paper was to promote the use of residual moringa seed powder (RMSP) for the enhancement of cereal-based products. RMSP is usually discarded after seed-oil extraction. This work also promotes zero-waste and rheological approaches.

In search of novel and sustainable food products with high nutritional value, cold-pressed Moringa oleifera Lam. seeds residue (RMSP) was used for incorporation in muffin formulations. Wheat flour was partially substituted (0%, 1%, 3%, 5%, 7% and 9%) by RMSP. Sodium (Na), calcium (Ca) and iron (Fe) contents were quantified through atomic absorption spectrometry; protein, through the Kjeldahl method followed by AACC Method 46–13.01; and, fat content, by a modified version of AACC Method 30–25.01a. Analysis of variance (ANOVA) and Tukey tests were performed to determine significant differences between formulations at 95% reliability using Minitab® software. Furthermore, simple viscosity studies of the dough mixture were carried in a Brookfield DV-III Ultra Rheometer; Matlab® curve-fitting tool was used for obtaining the best non-Newtonian equation that modeled experimental data. Subsequently, computational fluid dynamics (CFD) simulations of non-Newtonian fluids along a segmented pipe were carried out in Comsol Multiphysics® software to depict the importance of modeling non-Newtoning fluids for downstream processes.

RMSP significantly (p < 0.0001) increased protein and Fe content for the 7% and 9% formulations; it dramatically changed Na and Ca content in all formulations, while fat remained constant.

The development of this type of product is an opportunity for communities that grow and harvest moringa as well as for food industries which can take advantage of moringa by-products for several subsequent processing.

For the first time, it was found that dough formulations with RMSP presented a pseudo-plastic and thixotropic behavior. In addition, the use of lignocellulosic by-products such as RMSP incorporates an added value to food products. In this case, it was demonstrated that moringa seed residue enhanced nutritional value to muffins and provided coagulant/flocculant action, which is essential during dough preparation.