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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.

This paper outlines methods and results of wetting, leaching and adhesion analyses on copper thick film conductors over alumina and multilayer glasses after different processing conditions. The intention is to provide a better background for evaluating and optimising materials and processing conditions in copper thick films and working out quick, reliable and quantitative methods for better characterisation of copper conductors in production. For these reasons the following methods were used: (a) wetting and leaching analyses with a scanning wetting balance, working in nitrogen, (b) pull tests with solder contacts on copper thick film conductors after soldering, ageing and thermal cycling, and (c) some additional surface analyses (REM, EDX, Auger) for a better understanding of copper pastes and their material interactions, when processed under different conditions. The results are summarised under three general aspects: surface structure and wetting of copper thick films, wetting and leaching of various copper thick films after different processing conditions, and finally the influence of different wetting properties of such surfaces on the solder adhesion strength after soldering, ageing and thermal cycling. The results give good insight into the various interactions of copper thick films with their substrate materials and confirm the ability of the described wetting and leaching analyses for these purposes.

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.

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.

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.

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.

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.

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.

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.

This paper investigates wetting and infiltration of zirconium diboride by copper and copper/boron alloys in order to more effectively create electrodes for electrical discharge machining.

A high temperature furnace outfitted with a video recording system was utilized to observe wetting angles between molten copper alloys and zirconium diboride at various temperatures. A parallel, investigation of the thermodynamics involved with oxidation in the system was also undertaken.

This study showed that zirconium diboride can be wet by pure copper under carefully controlled conditions where oxygen contamination is minimized, and that the wetting angle increases with increasing temperature. Thermodynamic calculations reinforce the contention that oxygen contamination is the key barrier to wetting and infiltration. The addition of boron to copper significantly improves the wetting characteristics, and enables wetting and infiltration under higher oxygen contamination conditions.

This study illustrated that boron must be added to copper to achieve infiltration when surface oxides are present.

Infiltration of porous 3D green shapes of ceramics and metals is a common method for producing metal and ceramic components using rapid prototyping. Good wetting of the porous material by the infiltrant material is necessary for successful infiltration using capillary forces. This paper illustrates the alloys and conditions under which it is possible to produce electrodes of zirconium diboride/copper using rapid prototyping.

The purpose of this paper is to propose the materials structure-wetting behaviour relationships and to show their peculiarities for some types of surgical woven fabrics and applications of liquids.

To show the effects of fabrics structure on wetting behaviour of surgical textile materials, the special structural indices in terms of yarns and filaments lateral area were used.

It was shown good correlation between total lateral area of filaments in unit area of woven fabrics and wetting contact angle of liquid drops on the tested samples. Probably due to different structure of woven fabrics at a level of fibres, another index, i.e. total lateral area of yarns in unit area of fabrics, is not suitable to show clear effect on wetting behaviour of the samples. The possibilities of applications of relationships for several types of textile materials and liquids were indicated.

To date there are no investigations concerning relationships between special structural properties of the surgical woven fabrics and their wetting behaviour. On a basis of the proposed approach into fabrics structure evaluation, this study developed analysis and some types of new equations for prediction of wetting contact angle of the materials.

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.

The availability of a wetting balance which can be easily interfaced to a microcomputer has made possible a practical receiving inspection solderability test for component leads that avoids the subjectivity of the present dip‐and‐look test. The wetting balance, in effect, detects the size and shape of the solder meniscus on the lead. Since it is the solder meniscus more than the degree of coverage that is evaluated by inspectors of the completed solder joint, the wetting balance provides a more realistic test of how well the components will perform on the PWA. The software that has been developed for the wetting balance is designed to make it easy for inspection workers to perform the test with a minimum of training. It asks for identification of the part, manufacturer, date code, purchase order number, etc., so that the final results are adequately documented. Use of a computer to present the results means that the wetting force as a function of time can be plotted as a normalised curve (automatically accounting for differences in number and size of leads), and also that the results can be accumulated in a factory computer for statistical quality control. For a given lot of components, there is usually little spread in the observed results. This indicates that a sample size as small as three is sufficient to characterise the lot. With further data accumulation, it should be possible to devise a skip‐lot sampling plan for those manufacturers showing consistently good solderability. Also, the accumulated results of lots from problem manufacturers, coupled with microscopic studies of the causes of poor solderability, can be used as a basis for negotiations. The results are reproducible from one plant to another because they do not require visual interpretation. Judicious application of this method of solderability testing by a component user should allow removal of problem lots (for return or solderability enhancement), and therefore lead to a virtual elimination of solderability‐related defects observed after PWA soldering. Widespread application by component manufacturers (after burn‐in) should lead to a virtual elimination of cases of shipping unsolderable components.

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.

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.

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.

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.

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

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

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.

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.

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.

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.

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.

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.