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Article
Publication date: 1 March 1992

M.A. Kwoka and P.D. Mullenix

Visual inspection remains the dominant method of assessing component lead solderability and finished board solder joint quality. In recent years the wetting balance has…

Abstract

Visual inspection remains the dominant method of assessing component lead solderability and finished board solder joint quality. In recent years the wetting balance has received much attention as an attractive alternative to the inherently subjective visual inspection method of assessing component termination solderability. Whether direct visual inspection or wetting balance methods are used, the method can be shown to be effective only if the results are in agreement with board‐level soldering performance. This paper addresses the issue of the agreement of visual board‐level solder joint quality with both visual ‘dip and look’ solderability assessment and wetting balance measurement of the components prior to board assembly. A description of visual ‘dip and look’ solderability test assessment and of wetting balance methodology for components is presented, and a compendium of wetting balance tests and indices are documented in the Appendix. The experimental strategy employed is outlined, and details of the experimental technique (including the equipment, materials and component sample preparations) are provided. The experimental results present a comparison of both ‘dip and look’ visual solderability assessment and wetting balance measures with regard to actual board‐level soldering performance. The ability of the various assessment methods to predict board level defects is also explored.

Details

Soldering & Surface Mount Technology, vol. 4 no. 3
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 1 April 1989

K.M. Lin and F.H. Friend

With the increased use of surface‐mounted devices, both the component density and the board complexity are greatly increased on many circuit pack assemblies. Good…

Abstract

With the increased use of surface‐mounted devices, both the component density and the board complexity are greatly increased on many circuit pack assemblies. Good solderability for the components as well as for the printed circuit boards has become one of the most important elements in achieving the ultra‐high efficiency and quality required of an assembly soldering process in today's competitive environment. Solderability evaluation generally uses the ‘dip and look’ method that relies entirely on the individual inspectors' often inconsistent interpretations resulting from the examination of the specimen dip‐tested in a molten solder bath. This method is subjective, so the results can vary from person to person and from day to day. In addition, the sensitivity of such a method is inadequate in discerning the differences in solder wetting characteristics of very small device leads and terminations. Consequently, components with marginal or even bad solderability may pass through inspection and move onto the production line to cause many easily avoidable defects and their subsequent repairs. A sensitive and quantitative wetting balance method has been studied with the purpose of developing a better alternative to the ‘dip and look’ procedure. Special sample holders and test conditions have been developed for testing various types of components and printed circuit board coupons. Examples of solderability testings are provided to illustrate the capability of the instrument when proper testing procedures are followed. More effort is under way to simplify the test procedure, and to establish a practical solderability test standard for the wetting balance method.

Details

Circuit World, vol. 16 no. 1
Type: Research Article
ISSN: 0305-6120

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Article
Publication date: 1 January 1990

C. Lea

The subject of the quantitative measurement of solderability of electronic components is introduced. The wetting balance in various configurations and modes of operation…

Abstract

The subject of the quantitative measurement of solderability of electronic components is introduced. The wetting balance in various configurations and modes of operation is being used as the focal point to establish a quantitative measurement capability for solderability of conventional leaded components, surface mounting components and printed circuit interconnections. The principles of operation of the wetting balance and the factors that influence the measurement are discussed. This paper is the first of a series that will cover the development of traceable reference standards for wetting balance calibration, the influence of instrumental design on the measurement, the standardisation of the measurement procedures, the choice and evaluation of a solderability index for the dynamic measurement, and the traceability of the measurement to international standards.

Details

Soldering & Surface Mount Technology, vol. 2 no. 1
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 1 February 1989

L.‐G. Klang and M. Nylén

When testing SMDs with a wetting balance, some of the test parameters have a much greater influence on the wetting force and wetting time than others. It was found that…

Abstract

When testing SMDs with a wetting balance, some of the test parameters have a much greater influence on the wetting force and wetting time than others. It was found that the most important parameters were the type of flux, the temperature and the immersion depth. These three parameters were thoroughly studied and finally it was possible to make a suggestion for the values that these parameters should have. To evaluate the wetting curve, different methods were studied. The method chosen was to divide the wetting force by the wettable perimeter and this was called the normalised wetting force, measured in mN/m. All of the acceptable passive components tested had normalised wetting forces over 50 mN/m; for SOT‐23s the figures were over 250 mN/m. The normalised wetting forces were reached within 1.5 s in both cases. The main conclusion drawn from the tests was as follows: it seems possible to define one point for what is to be called good or bad solderability. This point will be 50 mN/m for passive chip components and 250 mN/m for SOT‐23s, to be reached within 1.5 s.

Details

Soldering & Surface Mount Technology, vol. 1 no. 2
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 6 April 2012

Przemyslaw Fima, Tomasz Gancarz, Janusz Pstrus, Krystyna Bukat and Janusz Sitek

The purpose of this paper is to study the effect of copper concentration in near‐eutectic liquid SAC solders on their thermophysical properties: viscosity, surface…

Abstract

Purpose

The purpose of this paper is to study the effect of copper concentration in near‐eutectic liquid SAC solders on their thermophysical properties: viscosity, surface tension, density; as well as wetting behavior on copper substrates at 523 K.

Design/methodology/approach

Viscosity, surface tension, and density were studied over a broad range of temperatures with the recently developed Roach‐Henein method. The obtained results were compared with the data from modified capillary, maximum bubble pressure, wetting balance and dilatometric measurements. Wetting angles measured with wetting balance method were compared with the results of sessile drop measurements.

Findings

The results obtained indicate that increasing concentration of copper in the alloy results in higher density, surface tension and viscosity, but differences resulting from copper concentration on wettability are relatively small. At 523 K, the density is: 7.097, 7.186, 7.232 g cm−3, the surface tension is: 538.1, 553.5, 556.7 m Nm−1, the viscosity is: 2.173, 2.227, 2.467 mPas, respectively, for alloys containing 0.41, 1.01 and 1.61 wt% of Cu. Wetting angles on copper substrates are similar within a margin of error for all compositions. The results of present study are compared with the available literature data and a relatively good agreement is observed.

Originality/value

This paper provides the data of thermophysical properties of widely‐used SAC solders including viscosity, of which there is little data in the literature. It is confirmed that the increased copper concentration increases viscosity, yet this effect is small and does not correlate with the wetting behavior.

Details

Soldering & Surface Mount Technology, vol. 24 no. 2
Type: Research Article
ISSN: 0954-0911

Keywords

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Article
Publication date: 3 February 2012

Krystyna Bukat, Janusz Sitek, Marek Koscielski, Zbigniew Moser, Wladyslaw Gasior and Janusz Pstrus

The purpose of this article is to establish why the wetting on PCBs with SnCu (HASL) and Snimm finishes in the presence of a flux is better than the wetting of those on a…

Abstract

Purpose

The purpose of this article is to establish why the wetting on PCBs with SnCu (HASL) and Snimm finishes in the presence of a flux is better than the wetting of those on a copper substrate. The practical aspect of the obtained results is the main goal of these investigations.

Design/methodology/approach

The authors applied the wetting balance method for the wetting measurements at 230 and 250°C, in nitrogen atmosphere, in the presence of the ORM0 type flux. The PCBs with the SnCu (HASL) and Snimm finishes were investigated in the state “as received”. To establish the wetting properties of the SnCu (HASL) and Snimm finishes on the PCBs, wetted by the investigated SnZnBiIn alloys, the SEM and EDX analyses were performed.

Findings

The authors obtained very good wetting results of the PCBs with the SnCu and Snimm finishes, wetted by the SnZn7Bi3In4 alloys. By applying the SEM and EDX methods, it was possible to establish that the barrier layer which was created during the HASL process between the copper and the SnCu solder is efficient enough to protect the copper against the influence of the Zn atoms from the SnZn7Bi3In4 solder. This is the reason for an improvement of the wetting properties. An immersion tin finish does not create such barrier layer with the copper. It results in a worse wetting than for the SnCu finishes but a better one than that for the copper. Immersion tin dissolves in the alloys during the soldering and this process delays the reaction between the copper and the Zn atoms from the SnZn7Bi3In4 solder.

Research limitations/implications

It is suggested that further studies are necessary for the confirmation of the practical application, but they should be limited to the reliability of the solder joint performance.

Practical implications

The best wetting results of the PCBs with “tin finishes”, especially with SnCu, wetted by the SnZn7Bi3In4 alloy, at 230 and 250°C and in nitrogen atmosphere, suggest a possibility of a practical usage of the tin‐zinc‐bismuth‐indium alloys for soldering in electronics.

Originality/value

The wetting balance method combined with the SEM and EDX analyses were used as the quickest way to determine the mechanism of the better wettability properties in the case of the PCBs with the SnCu and Snimm finishes, wetted by the SnZn7Bi3In4 alloy, compared to those of the PCBs on the Cu substrate.

Details

Soldering & Surface Mount Technology, vol. 24 no. 1
Type: Research Article
ISSN: 0954-0911

Keywords

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Article
Publication date: 1 January 1990

C. Lea and W.A. Dench

The wetting balance is used for the measurement of solderability of electronic components. The wetting force is measured dynamically and the technique gives information…

Abstract

The wetting balance is used for the measurement of solderability of electronic components. The wetting force is measured dynamically and the technique gives information about both the degree and the speed of wetting. For practical quality assessment of electronic components, a simple‐to‐use index is required that incorporates the data on both degree and speed of wetting. The index must also have a uniform discrimination between different wetting properties, across the full range encountered in practical soldering. This paper reviews critically the numerous indices suggested in the literature, and supports with quantitative data the choices previously made subjectively in some soldering standards.

Details

Soldering & Surface Mount Technology, vol. 2 no. 1
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 21 September 2010

K. Bukat, J. Sitek, M. Kościelski, Z. Moser, W. Gąsior and J. Pstruś

The purpose of this paper is to investigate the influence of Bi additions on the wetting properties of SnZn7Bi alloys (Bi=1 and 3 per cent by mass) on a copper substrate…

Abstract

Purpose

The purpose of this paper is to investigate the influence of Bi additions on the wetting properties of SnZn7Bi alloys (Bi=1 and 3 per cent by mass) on a copper substrate and printed circuit boards (PCBs) with lead‐free finishes (SnCu, immersion Sn, Ni/Au, organic solderability preservative) in the presence of fluxes. The practical implications of the results is the main purpose of these investigations.

Design/methodology/approach

A wetting balance method was used for wetting measurements at 230 and 250°C in nitrogen and air atmospheres in the presence of ORM0‐ or ROL0‐type fluxes. The PCBs were investigated ‘as received’ and after accelerated aging. The analysis of variance (ANOVA) analysis was performed in order to explain how the main factors of the experiments (the Bi content in the alloy (1 or 3 per cent), the test temperature and the test atmosphere) influenced the wetting ability of SnZn7Bi on Cu substrates.

Findings

As expected, a higher temperature and a higher Bi content in the alloy favoured the wetting of the copper substrate in the presence of the ORM0‐type flux in a nitrogen atmosphere. These results were confirmed by ANOVA analysis. Very good results were also obtained for the SnZn7Bi3 alloy's wettability on “tin coatings” on PCBs (SnCu and immersion Sn) both “as received” and after aging, in the presence of the ORM0‐type flux, for all the applied testing conditions (in both temperatures and N2 and air atmospheres). The less active flux (ROL0) caused a worsening of the alloy's wettability properties; however, the PCBs with SnCu and immersion Sn finishes maintained their wettability, even after aging, at very good and good levels, respectively.

Research limitations/implications

It is suggested that further studies are necessary for confirmation of the practical application, but they should be limited to the soldering of SnZnBi3 on PCBs with “tin coatings” and the quality of the solder joint performance.

Practical implications

The best SnZn7Bi3 wetting results on PCBs with “tin coatings” (SnCu and immersion Sn) at 230 and 250°C and in N2 and air atmospheres suggest the possibility of a practical usage of the tin‐zinc‐bismuth alloys for soldering in electronics using both the ORM0‐type flux and the even less active ROL0‐type flux, which are currently used in industrial lead‐free soldering processes.

Originality/value

The wetting balance method, combined with ANOVA was used as the quickest way to determine the wettability properties of SnZn7Bi on Cu substrates. Wettability measurements were also performed on the SnZn7 and SnZn7Bi alloys with different lead‐free finishes, in different experimental conditions.

Details

Soldering & Surface Mount Technology, vol. 22 no. 4
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 1 December 1997

W. Liggett, K.‐W. Moon and C. Handwerker

An experimental method for measurement system improvement is presented and applied to development of a protocol for solderability measurement with a wetting balance

Abstract

An experimental method for measurement system improvement is presented and applied to development of a protocol for solderability measurement with a wetting balance. Protocol development is central to development of reliable monitoring systems for manufacturing. This paper illustrates the method with an experiment in which sets of nearly identical test leads, each with a different solderability, are obtained by steam ageing of hot‐solder‐dipped copper and then measured according to alternative protocols. The protocols entail different flux types and solder bath temperatures. This method can be used wherever solderability measurements are made and thus satisfies the need for in‐house refinement of wetting balance protocols.With the experimental method, one can both compare alternative measurement protocols and estimate the relative solderability of sets of test leads. The results of both depend on what feature of the wetting force curve one selects to portray solderability. The comparison of measurement protocols is based on what is variously called precision, sensitivity, or signal‐to‐noise ratio. The solderability estimates show that different physical properties of the test leads affect different parts of the wetting force curve, and that changes in the steam ageing procedure affect solderability in a generally predictable way.

Details

Soldering & Surface Mount Technology, vol. 9 no. 2
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 8 February 2008

R.S. Lai, K.L. Lin and B. Salam

To study the effect of Ag content on the melting temperature and wetting properties of Sn‐8.5Zn‐xAg‐0.01Al‐0.1Ga lead‐free Solders.

Abstract

Purpose

To study the effect of Ag content on the melting temperature and wetting properties of Sn‐8.5Zn‐xAg‐0.01Al‐0.1Ga lead‐free Solders.

Design/methodology/approach

The solder alloys used in the experiment were Sn‐8.5Zn‐xAg‐0.01Al‐0.1Ga (x=0, 0.1, 0.3, 0.5, 1 and 1.5). In this study, the alloys were initially studied using differential scanning calorimetry to determine their melting temperatures. Afterward, the solderability of the solders was studied using wetting balance and contact angle methods. Moreover, the microstructures of the solders were also investigated with an optical microscope, scanning electron microscope, energy dispersive X‐ray, X‐ray diffraction and electron probe micro analysis.

Findings

A small increase in Ag content in the Sn‐8.5Zn‐xAg‐0.01Al‐0.1Ga solders, from 0.1 to 1.0 wt%, has been found to lower their solidus temperature from 198.05°C to 190.20°C. A Ag content of 1.5 wt% increased the solidus temperature of the studied solder systems to 197.79°C. Furthermore, the study also found that the addition of silver lowered the wetting forces of the studied solders. The formation of multi‐intermetallic layers of Cu‐Zn and Ag‐Zn at the interface between the studied solders and copper might explain the reduction of the wetting forces.

Research limitations/implications

The silver contents in the studied Sn‐8.5Zn‐xAg‐0.01Al‐0.1Ga solders were limited to 0, 0.1, 0.3, 0.5, 1.0 and 1.5 wt%.

Practical implications

Useful literature for solder alloy designers and SMT engineers.

Originality/value

The paper provides the answers to the research question of what is the effect of silver content on the melting temperature and wetting properties of Sn‐8.5Zn‐xAg‐0.01Al‐0.1Ga solders.

Details

Soldering & Surface Mount Technology, vol. 20 no. 1
Type: Research Article
ISSN: 0954-0911

Keywords

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