Karel Dusek

Flux effect on void quantity and size in soldered joints

Abstract This article is focused on both macro and microvoids in soldered joints and the use of additional flux to reduce their frequency and minimize their negative effect on the soldered joint reliability. In total five fluxes were used, three were gel based (NC559, MTV-125R, TSF-6516) and two of them were liquid based (Topnik G-5, JBC FL-15). They were used within two solder pastes, both lead and lead-free. The reflow process was identical for all of the combinations and was within the range of manufacturer recommended profiles. The amount of voids was evaluated using X-ray analysis. It was found that the use of increased amount of proper flux, specifically flux with higher activity, in the solder paste may significantly lower the void occurrence.

Surface tension measurement of the solders by non-wetting specimen

The knowledge of actual value of surface tension is important for the understanding to several soldering aspects, such as wetting, joint shape, fluxing action and, particularly, for the quantification of solderability testing. High surface tension is required for wave soldering. This article deals with the surface tension measurement of the lead and lead-free solders. For our measurement we used one of the solderability evaluation methods known as the wetting balance method, which is used to measure wetting force. A wetting balance has been used for evaluation of solderability. This method is based on the measurement of the wetting force. We used a special technique to obtain the surface tension values of the measured solders. The measurement was carried out on the ninth different types of solders (lead and lead free) and on non-wetting measurement specimen (teflon, nonstick cylinder).

Study of Undercooling and Recalescence During Solidification of Sn62.5Pb36.5Ag1 and Sn96.5Ag3Cu0.5 Solders in Real Electronic Joints

Undercooling and recalescence were studied using the differential scanning calorimetry (DSC) method on real electronic systems. Two solder pastes, Sn62.5Pb36.5Ag1 and Sn96.5Ag3Cu0.5, were used for preparation of electronic joints. Various combinations of these solders and soldering pads with different surface finishes such as Cu, Cu-Ni-Au, Cu-Sn, and Cu-Sn99Cu1 were used. During melting of both pastes, the Sn and Sn99Cu1 surface finishes immediately dissolved in the solder and the Cu surface coating was exposed to the melt. Therefore, practically the same undercooling was found for the Cu, Cu-Sn, and Cu-Sn99Cu1 coatings. The lowest undercooling was found for the Cu-Ni-Au surface finish for both solder pastes. If two separated electronic joints were made on the sample, two separate peaks were found in the DSC signal during solidification. In the sample with only one joint, only one exothermic peak was found. These findings were observed for all paste/surface finish combinations. These data were analyzed, showing that this effect is a consequence of undercooling and recalescence: Latent heat released during solidification of the joint increases the surrounding temperature and influences all the processes taking place.

New method for determining correction factors for pin-in-paste solder volumes

Purpose This paper aims to present a new method to calculate the appropriate volume of solder paste necessary for the pin-in-paste (PIP) technology. By the aid of this volume calculation, correction factors have been determined, which can be used to correct the solder fillet volume obtained by an explicit expression. Design/methodology/approach The method is based on calculating the optimal solder fillet shape and profile for through-hole (TH) components with given geometrical sizes. To calculate this optimal shape of the fillet, a script was written in Surface Evolver. The volume calculations were performed for different fillet radiuses (0.4-1.2 mm) and for different component lead geometries (circular and square cross-sections). Finally, the volume obtained by the Evolver calculations was divided by the volume obtained by an explicit expression, and correction factors were determined for the varying parameters. Findings The results showed that the explicit expression underestimates the fillet volume necessary for the PIP technology significantly (15-35 per cent). The correction factors for components with circular leads ranged between 1.4 and 1.59, whereas the correction factors for square leads ranged between 1.1 and 1.27. Applying this correction can aid in depositing the appropriate solder paste volume for TH components. Originality/value Determining the correct volume of solder paste necessary for the PIP technology is crucial to eliminate the common soldering failure of TH components (e.g. voiding or non-wetted solder pads). The explicit expression, which is widely used for volume calculation in this field, underestimates the necessary volume significantly. The new method can correct this estimation, and can aid the industry to approach zero-defect manufacturing in the PIP technology.

Investigating the thixotropic behaviour of Type 4 solder paste during stencil printing

Purpose 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). Design/methodology/approach 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. Findings 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. Originality/value 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.

Problem with no-clean flux spattering on in-circuit testing pads diagnosed by EDS analysis

Abstract Surface Mount Technology (SMT) assembly often faces the issue of residues on In Circuit Testing (ICT) pads. These residues may have non-conductive character and therefore in-circuit test may mark tested product as failed though they would have worked normally. Since it is not possible to export such marked products, the total production quality decreases. In this work, we analyze the real manufacturing problem using Energy Dispersive Spectroscopy (EDS) analysis of the stains with the aim to find the possible source of residues that appear on the testing pads during the mass electronic assembly or during Printed Circuit Board (PCB) production. Analysis of potential source of residues together with its diagnostic and confirmation of its source is presented in this work.

Study of temperature profiles of the infrared continuous furnace

This paper deals with temperature profiles and temperature measurements on different experimental samples. Samples were made for illustrating problems that may occur in reflow-soldering technology that used IR emitter as a heat source. In this work we focus on the several problems which have the influence on temperature profile - problem with different volume of the components, problem with different emissive of the surfaces and problem with shadow effect of components. All measurements were accomplished on continuous furnace DIMA SMRO-0180. For measuring temperature profiles and temperatures we used profilometer KIC Explorer 2000.

Studies of surface mount technology and its risk analysis

Surface mount technology is commonly used technology in electronics assembly. It is a method where the components are mounted directly onto the surface of printed circuit board. This article deals with risk analysis of surface mount technology in electronics assembly. Risk analysis applies many methods of analysis with the focus on potential hazards. Its aim is to improve understanding of process and improve managing it. Risk is acceptable in case that it has a low impact on the process. In this article we try to highlight several problems, which happen in the surface mount technology during the design of electronics circuits and which have the bad influence on the total quality. We try to highlight problems during the production as well.

Image analysis of solder spread factor on different material types

This article deals with the image analysis of the solder spread factor on the different material types and surface finishes. The spread factor of the solders is one of the tools which should be used to solderability and wetability quantification. Two types of solders (Sn62Pb36Ag2, Sn95,5Ag4Cu0,5) four types of material (lead free H.A.L., passivated copper, immersion tin plating, chemical gold plating) ware used in experiment. Three types of different roughness of the surface finish were used in case of cooper material. The differences between the solder spread factor on the different types of material and surface finishes ware evaluated by image analysis of the spread factor surface.

Influence of mechanical stress and temperature aging on a change of electrical connection resistance

This article deals with the mechanical stress and the temperature aging of the lead and lead free soldered joints. Soldered joints have influence on a total quality of electronic assembly. Mechanical and temperature tests are mainly used for resistance evaluation of components, devices and whole products against stress. This stress takes effect during function, transport and storage of the devices. Mechanical stress and temperature aging can change electrical properties of the soldered joints, e.g. electrical resistance. Even a small change of the electrical resistance could cause the malfunction of the electrical equipment. This is especially in the case of electrical equipment with high current density. In this article, the changes of the electrical resistance of mechanically stressed and temperature aged soldered joints (lead Sn62Pb36Ag2 and lead free Sn95.5Ag4Cu0.5) are compared.