Viscoelastic properties of solder pastes (original) (raw)
Related papers
Rheological characterization of a solder paste for surface mount applications
Rheologica Acta, 2006
Solder pastes used in surface mount soldering techniques (SMT) are very complex suspensions containing high volumes of metallic powder in a carrier fluid. The rheological complexity results largely from the carrier fluid itself, which is a suspension of colloidal particles. In this work, we have characterized the rheological properties of a typical carrier fluid and its solder paste containing 64 vol.% metallic powder. A six-blade vane geometry was used to avoid wall slip and sample fracture. All measurements were carried out following pre-shearing and rest time in order to obtain reproducible results. Steady shear experiments showed that the solder paste was highly shearthinning and thixotropic. In oscillatory shear, the linear viscoelastic domain was found to be very narrow for both the suspending fluid and the paste. Frequency sweep tests in the linear domain revealed a gel-like structure with a nearly constant G′ for the suspending fluid and a slightly increasing G′ for the solder paste. From creep experiments, a yield stress of about 40 Pa was determined for the suspending fluid at temperatures between 25 and 40°C, and of 100 Pa at 4°C. A much larger yield stress, 480 Pa, was determined for the solder paste at 25°C.
Rheology of F620 solder paste and flux
Soldering & Surface Mount Technology, 2018
Purpose 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). Design/methodology/approach 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. Findings 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 ...
Journal of Materials Processing Technology, 2009
Solder pastes and isotropic conductive adhesives (ICAs) are widely used as a principal bonding medium in the electronic industry. This study investigates the rheological behaviour of the pastes (solder paste and isotropic conductive adhesives) used for flip-chip assembly. Oscillatory stress sweep test are performed to evaluate solid characteristic and cohesiveness of the lead-free solder pastes and isotropic conductive adhesive paste materials. The results show that the G (storage modulus) is higher than G (loss modulus) for the pastes material indicating a solid like behaviour. It result shows that the linear visco-elastic region for the pastes lies in a very small stress range, below 10 Pa. In addition, the stress at which the value of storage modulus is equal to that of loss modulus can be used as an indicator of the paste cohesiveness. The measured cross-over stress at G = G shows that the solder paste has higher stress at G = G compared to conductive adhesives. Creep-recovery test method is used to study the slump behaviour in the paste materials. The conductive adhesive paste shows a good recovery when compared to the solder pastes.
2016
Industry standards such as J-STD-005 and JIS Z 3284-1994 call for the use of viscosity measurement(s) as a quality assurance test method for solder paste. Almost all solder paste produced and sold use a viscosity range at a single shear rate as part of the pass fail criteria for shipment and customer acceptance respectively. As had been reported many times, an estimated 80% of the defects associated with the surface mount technology process involve defects created during the printing process. Viscosity at a single shear rate could predict a fatal flaw in the printability of a solder paste sample. However, false positive single shear rate viscosity readings are not unknown. Intuitively, solder paste is subjected to several shear rates during the printing process. A squeegee forcing paste into an aperture may be the highest, and most critical strain rate applied to solder paste during the process. Separation of the stencil from the printed circuit card may be the second most important...
Rheological characterisation and printing performance of Sn/Ag/Cu solder pastes
Materials & Design, 2009
Lead-free solder paste printing process accounts for majority of the assembly defects in the electronic manufacturing industry. The study investigates rheological behaviour and stencil printing performance of the lead-free solder pastes (Sn/Ag/Cu). Oscillatory stress sweep test was carried out to study the visco-elastic behaviour of the lead-free solder pastes. The visco-elastic behaviour of the paste encompasses solid and liquid characteristic of the paste, which could be used to study the flow behaviour experienced by the pastes during the stencil printing process. From this study, it was found that the solid characteristics (G 0 ) is higher than the liquid characteristic (G 00 ) for the pastes material. In addition, the results from the study showed that the solder paste with a large G 0 = G 00 has a higher cohesiveness resulting in poor withdrawal of the paste during the stencil printing process. The phase angles (d) was used to correlate the quality of the dense suspensions to the formulation of solder paste materials. This study has revealed the value of having a rheological measurement for explaining and characterising solder pastes for stencil printing. As the demand for lead free pastes increases rheological measurements can assist with the formulation or development of new pastes.
The rheological properties of solder and solar pastes and the effect on stencil printing
Rheologica Acta, 2000
Solar and solder pastes are widely used in the electronics industry. Solder paste is the principal joining medium in the assembly of surface mount components, whilst solar paste is used in the manufacture of semiconductor solar cells in the photo-voltaic industry. The stencil printing of both solder and solar pastes is a very important and critical stage in the assembly process. With miniaturisation of components, this is likely to continue. The challenge in stencil printing at such dimensions is in achieving repeatable deposition of both solar and solder pastes from print to print. To meet this challenge requires an understanding of the flow behaviour of both solar and solder pastes. The rheological properties of solar and solder pastes have been evaluated through three different types of experiments. Existing models were applied to compare their rheological behaviour under these schemes. One striking difference was that solar paste showed a higher viscosity than solder paste. Both solar and solder pastes were found to be non-Newtonian materials, showing a decrease in viscosity with increasing shear rates. In this paper we investigate the rheological properties of both solder and solar paste under steady shear and creep-recovery tests.
Measurements of solder paste viscosity during its tempering and aging
Proceedings of the 2014 37th International Spring Seminar on Electronics Technology, 2014
Solder paste printing is one of the most important steps in the surface mount technology, which has high influence on the resulting quality of solder joints. To achieve a good joint quality, the solder paste should have specific properties like adhesion, viscosity, size of the solder alloy particles, amount of flux etc. This paper is focused on the measurement of the solder paste viscosity during its tempering and aging with possibility of regeneration of solder paste properties by jelly flux. Three types of solder pastes were used in the experiment: Sn95.5Ag4Cu0.5, Sn96.5Ag3Cu0.5 and Sn62Pb36Ag2. Viscosity of solder paste is measured from storing temperature to the ambient temperature. Aging of solder pastes is made in ambient atmosphere. Regeneration of solder paste properties after aging was done by adding of jelly flux Amtech 4300/LF-4300-TF. The viscosity of pure solder paste before aging, pure solder paste after aging and solder paste after aging regenerated by jelly flux was measured by rotation viscometer Brookfield Synchroelectric Viscometer, model HBT. The article describes if the addition of jelly flux to the aged solder pastes regenerates their properties.
2007
The lack of understanding relating to the correlation between paste characteristics and print performance presents a challenge with regards to accurately predicting the outcome of the printing process. One such paste characteristic, the abandon time, is critical in reducing defects on a modern assembly line, due to the requirement of achieving an acceptable print after a delay in production. This study concerns the investigation of the abandon time for different lead-free solder paste formulations used for flip- chip assembly. The objective of the study is to determine the length of time a paste could be plausibly left on the stencil before the quality of print degrades. In the study, a series of viscosity and oscillation shear tests were carried out to aid with understanding the nature of the pastes. Results show that for all the pastes, there is a degradation of the pastes elastic and viscous behaviour after a period of 50 hours, thus demonstrating a breakdown in paste structure, which can be correlated to the deterioration of pastes printing quality. The results also show that increasing the length of the abandon time leads to an increase in the incidence of paste bridging, which is correlated to the decrease in storage and loss modulus from the oscillatory tests. The utility of the results of the study is in assisting paste manufacturers and process engineers in the identification of the process window with respect to the paste property changes with various abandon time scenarios, such as those experienced within a typical industrial production line.
Wall-slip effects in SnAgCu solder pastes used in electronics assembly applications
2009
Solder paste is the most important strategic bonding material used in the assembly of surface mount components in electronics manufacturing. As the trend towards miniaturisation of electronic products continues, there is an increasing demand for better understanding of the flow and deformation that is, the rheological behaviour of solder paste formulations. Wall slip plays an important role in characterising the flow behaviour of solder paste materials. The problem of wall slip arises due to the various attractive and repulsive forces acting between the solder particles and the walls of the measuring geometry. These interactions could lead to the presence of a thin solvent layer adjacent to the wall, which gives rise to slippage. In rheological measurements, slip effects can generally be avoided by using roughened surfaces for measuring geometries. In this paper, a novel technique is developed to study the effect of wall slip in the rheological measurements of lead-free solder paste. The viscosity and oscillatory data obtained for three different solder paste samples (from measuring geometries of different surface roughness) have been analysed and compared. In viscosity measurements, slip effects were dominant at low shear rates and the use of serrated surfaces was found to be quite effective in minimizing slip effects. Oscillatory measurements were also affected by roughening the surfaces of measuring geometries.
Flow processes in solder paste during stencil printing for SMT assembly
Journal of Materials Science: Materials in Electronics, 1995
Solder paste is used for reflow soldering of Surface Mount Devices (SMDs). In this paper we discuss how the various stages of the stencil printing cycle affect the rheological properties of the solder paste. First the heat generated in the paste roll is examined to see what effect it has on solder paste rheology, then we analyse in detail the process of paste withdrawal from a metal mask stencil and discuss those properties of solder paste that lead to a good print in terms of the size and shape of the solder paste particles, and their packing. In order to do this, we review some of the experiments and phenomena that have been shown to occur in dense suspensions, and see what aspects of that work are applicable to solder paste printing.