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Article

C. Melton

A quantitative dynamic solder wettability measurement was used to evaluate the effects of reflow processing on the wettability parameters associated with two non‐lead…

Abstract

A quantitative dynamic solder wettability measurement was used to evaluate the effects of reflow processing on the wettability parameters associated with two non‐lead bearing solders, 96.5% Sn/3.5% Ag and 58% Bi/42% Sn. An experimental design approach employing full factorial experiments was formulated to investigate the solder wetting dependence of the reflow parameters: atmosphere, peak reflow temperature, time above liquidus and metallisation. Solder wettability was determined with respect to the final degree of spread and the extent of solder wetting onto the lands of surface mount components. The solder alloy composition of 96.5% Sn/3.5% Ag was found to exhibit better wetting characteristics than the 58% Bi/42% Sn alloy. This wetting behaviour was enhanced under the reflow conditions of a nitrogen atmosphere and the use of a gold metallisation. The wetting of the conventional 63% Sn/37% Pb solder alloy was improved over the comparatively processed 58% Bi/42% Sn alloy. However, the 63% Sn/37% Pb solder alloy displayed a greater sensitivity to reflow atmosphere than the 96.5% Sn/3.5% Ag alloy, which generally exhibited better wetting characteristics than the Sn/Pb alloy.

Details

Soldering & Surface Mount Technology, vol. 6 no. 2
Type: Research Article
ISSN: 0954-0911

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Article

Min Wu and Bailin Lv

Viscosity is an important basic physical property of liquid solders. However, because of the very complex nonlinear relationship between the viscosity of the liquid…

Abstract

Purpose

Viscosity is an important basic physical property of liquid solders. However, because of the very complex nonlinear relationship between the viscosity of the liquid ternary Sn-based lead-free solder and its determinants, a theoretical model for the viscosity of the liquid Sn-based solder alloy has not been proposed. This paper aims to address the viscosity issues that must be considered when developing new lead-free solders.

Design/methodology/approach

A BP neural network model was established to predict the viscosity of the liquid alloy and the predicted values were compared with the corresponding experimental data in the literature data. At the same time, the BP neural network model is compared with the existing theoretical model. In addition, a mathematical model for estimating the melt viscosity of ternary tin-based lead-free solders was constructed using a polynomial fitting method.

Findings

A reasonable BP neural network model was established to predict the melt viscosity of ternary tin-based lead-free solders. The viscosity prediction of the BP neural network agrees well with the experimental results. Compared to the Seetharaman and the Moelwyn–Hughes models, the BP neural network model can predict the viscosity of liquid alloys without the need to calculate the relevant thermodynamic parameters. In addition, a simple equation for estimating the melt viscosity of a ternary tin-based lead-free solder has been proposed.

Originality/value

The study identified nine factors that affect the melt viscosity of ternary tin-based lead-free solders and used these factors as input parameters for BP neural network models. The BP neural network model is more convenient because it does not require the calculation of relevant thermodynamic parameters. In addition, a mathematical model for estimating the viscosity of a ternary Sn-based lead-free solder alloy has been proposed. The overall research shows that the BP neural network model can be well applied to the theoretical study of the viscosity of liquid solder alloys. Using a constructed BP neural network to predict the viscosity of a lead-free solder melt helps to study the liquid physical properties of lead-free solders that are widely used in electronic information.

Details

Soldering & Surface Mount Technology, vol. 32 no. 3
Type: Research Article
ISSN: 0954-0911

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Article

Md Hasnine

This paper aims to investigate the effect of In and Sb additions on the thermal behavior and wettability of Sn-3.5Ag-xIn-ySb (x = 0, 1.0 and 1.5 Wt.%, y = 0, 1.0, 1.4 and…

Abstract

Purpose

This paper aims to investigate the effect of In and Sb additions on the thermal behavior and wettability of Sn-3.5Ag-xIn-ySb (x = 0, 1.0 and 1.5 Wt.%, y = 0, 1.0, 1.4 and 2.1 Wt.%) solder alloys.

Design/methodology/approach

The thermal behavior of the Pb-free solder alloys was studied using differential scanning calorimetry. Wetting balance experiments were performed in accordance with the IPC standard, IPC-TM-650 and at a temperature of 260°C. Also, a solder spread test was performed on a Cu surface finish using the JIS-Z-3197 solderability standard.

Findings

It is shown that among the selected Sn-3.5Ag-xIn-ySb (x = 0, 1.0 and 1.5 Wt.%, y = 0, 1.0, 1.4 and 2.1 Wt.%) alloys, Sn-3.5Ag-1.5In-1Sb showed the lowest melting point and the lowest undercooling temperature. The best wettability was achieved when the In and Sb contents were approximately 1.5 and 1.0 Wt.%, respectively. The effect of the combined addition of In and Sb on solder spreadability on a Cu substrate was also demonstrated.

Originality/value

It was found that adding approximately 1.5 and 1.0 Wt.% of In and Sb, respectively, in Sn-3.5Ag solder provided the best wetting performance and improved the solder spreadability.

Details

Soldering & Surface Mount Technology, vol. 30 no. 4
Type: Research Article
ISSN: 0954-0911

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Article

Liang Zhang, Song-bai Xue, Li-li Gao, Yan Chen, Sheng-lin Yu, Zhong Sheng and Guang Zeng

The purpose of this paper is to investigate the effects of minor addition of the rare earth (RE) element cerium, Ce, on the microstructures and creep properties of…

Abstract

Purpose

The purpose of this paper is to investigate the effects of minor addition of the rare earth (RE) element cerium, Ce, on the microstructures and creep properties of Sn-Ag-Cu solder alloys.

Design/methodology/approach

The pure Sn, Sn-Cu alloy, Sn-Ag alloy and Cu-Ce alloy were used as raw materials. Sn-Ag-Cu alloys with different contents of RE Ce were chosen to compare with Sn-Ag-Cu. The raw materials of Sn, Sn-Cu alloy, Sn-Ag alloy, Cu-Ce alloy were melted in a ceramic crucible, and were melted at 550°C ± 1°C for 40 minutes. To homogenize the solder alloy, mechanical stirring was performed every ten minutes using a glass rod. During the melting, KC1 + LiCI (1.3:1), were used over the surface of liquid solder to prevent oxidation. The melted solder was chill cast into a rod.

Findings

It is found that the microstructure exhibits smaller grains and the Ag3Sn/Cu6Sn5 intermetallic compound (IMC) phases are modified in matrix with the addition of Ce. In particular, the addition of 0.03 wt.% Ce to the Sn-Ag-Cu solder can refine the microstructures and decrease the thickness of the IMC layers of Sn-Ag-Cu solder alloys. Meanwhile, thermodynamic analysis showed that these phenomena could be attributed to the reduction of the driving force for Cu-Sn IMC formation due to the addition of Ce. Results calculated using the thermodynamic method are close to the above experimental data. Thus, the optimum content of Ce in Sn-Ag-Cu solder alloys should be about 0.030 percent. Additionally, the effect of Ce on the creep rupture life of Sn-Ag-Cu soldered joints was studied. It was found that the creep rupture life may be increased up to 7.5 times more than that of the original Sn-Ag-Cu alloy, when Ce accounts for 0.030 percent.

Originality/value

This paper usefully investigates the effects of the RE cerium (Ce), on the microstructures and creep properties of Sn-Ag-Cu solder alloys, optimizing the quantity of Ce in the Sn-Ag-Cu solder alloy through a thermodynamic method and by creep-rupture life testing.

Details

Soldering & Surface Mount Technology, vol. 22 no. 2
Type: Research Article
ISSN: 0954-0911

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Article

Ervina Efzan Mhd Noor and Amares Singh

The aim of the present study was to gather and review all the important properties of the Sn–Ag–Cu (SAC) solder alloy. The SAC solder alloy has been proposed as the…

Abstract

Purpose

The aim of the present study was to gather and review all the important properties of the Sn–Ag–Cu (SAC) solder alloy. The SAC solder alloy has been proposed as the alternative solder to overcome the environmental concern of lead (Pb) solder. Many researchers have studied the SAC solder alloy and found that the properties such as melting temperature, wettability, microstructure and interfacial, together with mechanical properties, are better for the SAC solder than the tin – lead (SnPb) solders. Meanwhile, addition of various elements and nanoparticles seems to produce enhancement on the prior bulk solder alloy as well. These benefits suggest that the SAC solder alloy could be the next alternative solder for the electronic packaging industry. Although many studies have been conducted for this particular solder alloy, a compilation of all these properties regarding the SAC solder alloy is still not available for a review to say.

Design/methodology/approach

Soldering is identified as the metallurgical joining method in electronic packaging industry which uses filler metal, or well known as the solder, with a melting point < 425°C (Yoon et al., 2009; Ervina and Marini, 2012). The SAC solder has been developed by many methods and even alloying it with some elements to enhance its properties (Law et al., 2006; Tsao et al., 2010; Wang et al., 2002; Gain et al., 2011). The development toward miniaturization, meanwhile, requires much smaller solder joints and fine-pitch interconnections for microelectronic packaging in electronic devices which demand better solder joint reliability of SAC solder Although many studies have been done based on the SAC solder, a review based on the important characteristics and the fundamental factor involving the SAC solder is still not sufficient. Henceforth, this paper resolves in stating all its important properties based on the SAC solder including its alloying of elements and nanoparticles addition for further understanding.

Findings

Various Pb-free solders have been studied and investigated to overcome the health and environmental concern of the SnPb solder. In terms of the melting temperature, the SAC solder seems to possess a high melting temperature of 227°C than the Pb solder SnPb. Here, the melting temperature of this solder falls within the range of the average reflow temperature in the electronic packaging industry and would not really affect the process of connection. A good amendment here is, this melting temperature can actually be reduced by adding some element such as titanium and zinc. The addition of these elements tends to decrease the melting temperature of the SAC solder alloy to about 3°C. Adding nanoparticles, meanwhile, tend to increase the melting temperature slightly; nonetheless, this increment was not seemed to damage other devices due to the very slight increment and no drastic changes in the solidification temperature. Henceforth, this paper reviews all the properties of the Pb-free SAC solder system by how it is developed from overcoming environmental problem to achieving and sustaining as the viable candidate in the electronic packaging industry. The Pb-free SAC solder can be the alternative to all drawbacks that the traditional SnPb solder possesses and also an upcoming new invention for the future needs. Although many studies have been done in this particular solder, not much information is gathered in a review to give better understanding for SAC solder alloy. In that, this paper reviews and gathers the importance of this SAC solder in the electronic packaging industry and provides information for better knowledge.

Originality/value

This paper resolves in stating of all its important properties based on the SAC solder including its alloying of elements and nanoparticles addition for further understanding.

Details

Soldering & Surface Mount Technology, vol. 26 no. 3
Type: Research Article
ISSN: 0954-0911

Keywords

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Article

Dhafer Abdul Ameer Shnawah, Suhana Binti Mohd Said, Mohd Faizul Bin Mohd Sabri, Irfan Anjum Badruddin and Fa Xing Che

The purpose of this paper is to investigate the effects of small additions (0.1 and 0.3 wt%) of Fe on the bulk alloy microstructure and tensile properties of low…

Abstract

Purpose

The purpose of this paper is to investigate the effects of small additions (0.1 and 0.3 wt%) of Fe on the bulk alloy microstructure and tensile properties of low Ag‐content Sn‐1Ag‐0.5Cu lead‐free solder alloy.

Design/methodology/approach

Sn‐1Ag‐0.5Cu, Sn‐3Ag‐0.5Cu and Sn‐1Ag‐0.5Cu containing 1 and 3 wt.% Fe solder specimens were prepared by melting pure ingots of Sn, Ag, Cu and Fe in an induction furnace and subsequently remelting and casting to form flat dog‐bone shaped specimens for tensile testing. The solder specimens were subjected to tensile testing using an INSTRON tester with a loading rate 10‐3 s‐1. To obtain the microstructure, the solder samples were prepared by dicing, molding, grinding and polishing processes. The microstructural analysis was carried out using scanning electron microscopy/Energy Dispersive X‐ray spectroscopy. Electron backscatter diffraction (EBSD) analysis was used to identify the IMC phases.

Findings

In addition to large primary β‐Sn grains, the addition of Fe to the SAC105 alloy formed large circular shaped FeSn2 IMC particles located in the eutectic regions. This had a significant effect in reducing the elastic modulus and yield strength and maintaining the elongation at the SAC105 level. Moreover, the additions of Fe resulted in the inclusion of Fe in the Ag3Sn and Cu6Sn5 IMC particles. The additions of Fe did not have any significant effect on the melting behaviour.

Research limitations/implications

The paper provides a starting‐point for studying the effect of minor additions of Fe on the drop impact and thermal cycling reliability of SAC105 alloy considering the bulk alloy microstructure and tensile properties. Further investigations should be undertaken in the future.

Originality/value

The effect of Fe addition on the bulk alloy microstructure and tensile properties of the SAC105 alloy has been studied for the first time. Fe‐containing SAC105 alloy may have the potential to increase the drop impact and thermal cycling reliability compared with the standard SAC105 alloy.

Details

Soldering & Surface Mount Technology, vol. 24 no. 4
Type: Research Article
ISSN: 0954-0911

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Article

Dhafer Abdul Ameer Shnawah, Mohd Faizul Bin Mohd Sabri, Irfan Anjum Badruddin and Suhana Said

The purpose of this paper is to discuss the reliability of board level Sn‐Ag‐Cu (SAC) solder joints in terms of both thermal cycling and drop impact loading conditions…

Abstract

Purpose

The purpose of this paper is to discuss the reliability of board level Sn‐Ag‐Cu (SAC) solder joints in terms of both thermal cycling and drop impact loading conditions, and further modification of the characteristics of low Ag‐content SAC solder joints using minor alloying elements to withstand both thermal cycle and drop impact loads.

Design/methodology/approach

The thermal cycling and drop impact reliability of different Ag‐content SAC bulk solder will be discussed from the viewpoints of mechanical and micro‐structural properties.

Findings

The best SAC composition for drop performance is not necessarily the best composition for optimum thermal cycling reliability. The content level of silver in SAC solder alloys can be an advantage or a disadvantage depending on the application, package and reliability requirements. The low Ag‐content SAC alloys with different minor alloying elements such as Mn, Ce, Bi, Ni and Ti display good performance in terms of both thermal cycling and drop impact loading conditions.

Originality/value

The paper details the mechanical and micro‐structural properties requirements to design a robust bulk SAC solder joint. These properties provide design and manufacturing engineers with the necessary information when deciding on a solder alloy for their specific application.

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Article

M. Reid, J. Punch, M. Collins and C. Ryan

The purpose of this paper is to examine the microstructure and evaluate the intermetallic compounds in the following lead‐free solder alloys: Sn98.5Ag1.0Cu0.5 (SAC105) Sn…

Abstract

Purpose

The purpose of this paper is to examine the microstructure and evaluate the intermetallic compounds in the following lead‐free solder alloys: Sn98.5Ag1.0Cu0.5 (SAC105) Sn97.5Ag2.0Cu0.5 (SAC205) Sn96.5Ag3.0Cu0.5 (SAC305) and Sn95.5Ag4.0Cu0.5 (SAC405).

Design/methodology/approach

X‐ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to identify the main intermetallics formed during solidification. Differential scanning calorimetry (DSC) was used to investigate the undercooling properties of each of the alloys.

Findings

By using XRD analysis in addition to energy dispersive spectroscopy (EDS) it was found that the main intermetallics were Cu6Sn5 and Ag3Sn in a Sn matrix. Plate‐like ε‐Ag3Sn intermetallics were observed for all four alloys. Solder alloys SAC105, SAC205 and SAC305 showed a similar microstructure, while SAC405 displayed a fine microstructure with intermetallic phases dense within the Sn matrix.

Originality/value

Currently, low‐silver content SAC alloys are being investigated due to their lower cost, however, the overall reliability of an alloy can be greatly affected by the microstructure and this should be taken into consideration when choosing an alloy. The size and number of Ag3Sn plate‐like intermetallics can affect the reliability as they act as a site for crack propagation.

Details

Soldering & Surface Mount Technology, vol. 20 no. 4
Type: Research Article
ISSN: 0954-0911

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Article

J. Seyyedi

An empirical study was conducted to determine the thermal fatigue behaviour of 1.27 mm pitch, J‐bend and gullwing surface mount solder joints, manufactured with four…

Abstract

An empirical study was conducted to determine the thermal fatigue behaviour of 1.27 mm pitch, J‐bend and gullwing surface mount solder joints, manufactured with four low‐temperature solders. Selected solder alloys were: 58Bi‐42Sn (wt %), 43Sn‐43Pb‐14Bi, 52ln‐48Sn and 40ln‐40Sn‐20Pb. Accelerated thermal cycling was used in conjunction with metallographic analysis and mechanical (pull) strength measurement to test their behaviour. The relative merit of each solder composition was determined by comparing it with 63Sn‐37Pb solder, subjected to identical testing conditions. The strength decreased linearly with increased number of thermal cycles for gullwing solder joints of all four solder alloys. The fatigue lifetime was relatively longer for 58Bi‐42Sn and 40ln‐40Sn‐20Pb than for other alloys, but significantly lower than that obtained with 63Sn‐37Pb solder. No discernible degradation of strength was observed with the J‐bend solder joints of any solder alloy, even after the completion of 6000 thermal cycles. Thermal fatigue resistance of the latter joints was attributed to a more favourable coefficient of thermal expansion (CTE) mismatch. Solder joint cracking occurred only in gullwing components soldered with 52ln‐48Sn, 40ln‐40Sn‐20Pb and 43Sn‐43Pb‐14Bi alloys, after 1000 or 2000 thermal cycles. The crack initiated on the outside surface of the solder fillet, and appeared to propagate through both phases of the microstructure. The stress‐induced heterogeneous coarsening of the microstructure was evident only with 43Sn‐43Pb‐14Bi solder, although not as prevalent as that usually observed with eutectic Sn‐Pb solder. Fatigue cracks were absent from solder joints of 58Bi‐42Sn and 63Sn‐37Pb alloys.

Details

Soldering & Surface Mount Technology, vol. 5 no. 1
Type: Research Article
ISSN: 0954-0911

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Article

Benlih Huang, Arnab Dasgupta and Ning‐Cheng Lee

Tombstoning and voiding have been plaguing the surface mount assembly industry for decades. The recent global move toward lead‐free soldering and the extensive adoption of…

Abstract

Purpose

Tombstoning and voiding have been plaguing the surface mount assembly industry for decades. The recent global move toward lead‐free soldering and the extensive adoption of microvia technology further aggravate the problems. The present study investigates the impact of SnAgCu (SAC) alloy composition on these important issues.

Design/methodology/approach

In this study, tombstoning and voiding at microvias are studied for a series of SAC lead‐free solders, with an attempt to identify a possible “composition window” for controlling these problems. Properties which may be related to these problems, such as alloy surface tension, alloy melting pattern, and solder wetting behaviour, were investigated in order to assess the critical characteristics required to control these problems.

Findings

The results indicate that the tombstoning of SAC alloys is greatly influenced by the solder composition. Both the wetting force and the wetting time at a temperature well above the melting point have no correlation with the tombstoning frequencies. Because the tombstoning is caused by imbalanced wetting forces, the results suggest that the tombstoning may be controlled by the wetting at the onset of the paste melting stage. A maximum tombstoning incidence was observed for the 95.5Sn3.5Ag1Cu alloy. The tombstoning rate decreased with increasing deviation in Ag content from this composition. A differential scanning calorimetry (DSC) study indicated that this was mainly due to the increasing presence of the pasty phase in the solders, which result in a slower wetting speed at the onset of solder paste melting stage. Surface tension plays a minor role, with lower surface tension correlating with a higher tombstoning rate. The voiding rate at the microvias was studied by employing simulated microvias. The voiding level was lowest for the 95.5Sn3.8Ag0.7Cu and 95.5Sn3.5Ag1Cu alloys, and increases with a further decrease in the Ag content. The results indicate that voiding at microvias is governed by the via filling and the exclusion of fluxes. The voiding rate decreased with decreasing surface tension and increasing wetting force, which in turn is dictated by the solder wetting or spreading. Both low surface tension and high solder wetting prevents the flux from being entrapped within a microvia. A fast wetting speed may also facilitate reducing voiding. However, this factor is considered not as important as the final solder coverage area.

Research limitations/implications

In general, compositions which deviate from the ternary eutectic SAC in Ag content, particularly with a Ag content lower than 3.5Ag, exhibit a greater solid fraction at the onset of melting, resulting in a lower tombstoning rate, presumably due to a slower wetting speed. The SAC compositions with an Ag content lower than 3.5 per cent, such as 2.5Ag, resulted in a lower tombstoning rate with minimal risk of forming Ag3Sn intermetallic platelets. On the other hand, ternary eutectic SAC exhibits a lower surface tension resulting in an easier solder spread or solder wetting, and consequently exhibit a higher tombstoning frequency and a lower incidence of voiding.

Practical implications

Provides a solution to the tombstoning problem in lead‐free soldering.

Originality/value

The present study provided a solution to the tombstoning problem encountered in lead free soldering by controlling the SAC solder alloy compositions.

Details

Soldering & Surface Mount Technology, vol. 17 no. 3
Type: Research Article
ISSN: 0954-0911

Keywords

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