Purpose
The reliability of 0603 size resistors’ solder joints formed with Infrared and Vapour Phase soldering was investigated. The intermetallic layer of the joints was analysed based on image ...processing algorithm automatically.
Design/methodology/approach
For the reliability analyses, the aging method was a Highly Accelerated Stress Test with +105 °C maximum temperature, fully saturated (100%) relative humidity on +0.5 atm. overpressure. The joints were characterised based on the thickness of their intermetallic layer and on their shear strength in as-reflowed stage, and after 400, 800, 1200, 1600, 2000 hours of HAST. An image processing algorithm was developed to measure the thickness of the intermetallic layers on cross-sectional Scanning Electron Microscopy images automatically.
Findings
The increase of the intermetallic layer thickness is lower in the case of HAST aging compared to other methods. The thickness increment of the Cu6Sn5 layer was higher for Infrared and lower for Vapour Phase soldering; the Cu3Sn layer cannot be inspected even after 2.000h of HAST aging. The results of shear strength measurements show better reliability for Vapour Phase soldered joints.
Practical implications
The developed image processing method is applicable to obtain quantitative results about the intermetallic layers in an effective, fast way.
Originality/value
There is a lack of information in the literature regarding the reliability comparison of solder joints formed with Vapour Phase and conventional reflow processes. Thus, we performed research about the lifetime of solder joints formed with Vapour Phase and IR reflow method.
•Self-alignment of surface mounted passive components was investigated.•Solder profile of surface mounted components was simulated with Surface Evolver.•Solder profile simulations were verified with ...cross-sections of solder joints.•The degree of self-alignment parallel to longer side of the components is lower.•Self-alignment parallel to longer side can be improved with sidewall metallization.
In my research a 3D model was created to investigate the restoring force arising and the self-alignment occurring during reflow soldering; and simulations were performed to examine the assumptions given by the model. Besides, experiments were carried out to verify both the assumptions and the simulation predictions. Passive components with the size of 0603 (1.5×0.75mm) were placed with intended misplacements and their position was measured before and after soldering. Three cases were examined: how misplacements perpendicular to the longer sides of components affects the restoring force, how parallel misplacements affect the same, and how a sidewall metallization on the component influences that. Based on the results, it is shown that the degree of restoring force is higher in the case of misplacements perpendicular to the longer side of components (x-direction) than in the case of misplacements parallel to that (y-direction). However, in the case of y-direction misplacements, the restoring force increases when sidewall metallization on the components is present.
•Numerical modelling of the a Vacuum Vapour Phase Soldering System was done.•Low vapour pressure is applied to decrease the gas voids in the solder joints.•3D flow model was developed with RANS ...equations and standard k-ε turbulence method.•Vapour suctioning has considerable effects on the heat transfer processes of the soldering.•Heat loss of the soldering chamber during the vapour suctioning can be decreased with appropriate settings.
The heat and mass transport processes were investigated with numerical simulations in a vacuum vapour phase soldering system during the vapour suctioning process. Low vapour pressure/concentration is applied during vacuum soldering to decrease the number of gas voids in the solder joints. Three-dimensional numerical flow model was developed which based on the Reynolds averaged Navier-Stokes equations with the standard k-ε turbulence method. The decrease of the vapour concentration and its effects on the solder joints were studied in the case of different oven settings. It was found that vapour suctioning has considerable effects on the heat transfer processes in the soldering chamber which might lead to early solidification of the solder joints and reduces the efficiency of the void removal. Different oven settings were simulated in order to decrease the heat loss of the soldering chamber during the vapour suctioning. It was shown that with appropriate setting of the vacuum vapour phase soldering technology, the efficiency of the void removal can be increased.
Stencil printing is the most crucial process in reflow soldering for the mass assembly of electronic circuits. This paper investigates different machine learning-based methods to predict the ...essential process characteristics of stencil printing: the area, thickness, and volume of deposited solder paste. The training dataset was obtained experimentally by varying the printing speed (from 20 to 120 mm/s), the size (area ratio from 0.35 to 1.7) of stencil apertures, and the particle size (characterized by a log-normal distribution) in the solder paste. Various machine learning-based methods were assessed; ANFIS–adaptive neuro-fuzzy inference systems; ANN artificial neural networks (with different learning methods); boosted trees, regression trees, SVM–support vector machines. Each method was optimized and fine-tuned with hyperparameter optimization, and the overfitting phenomenon was also prevented with cross-validation. The regression tree was the best performing approach for modelling the stencil printing, while ANN with the Bayesian regularization learning method was only slightly worse. The presented methodology for fine-tuning, parameter optimization, and the comparison of different machine learning-based methods can easily be adapted to any application field in electronics manufacturing.
The kinetics of Sn whisker growth was investigated on vacuum-evaporated Sn thin-films. Sn film layers were deposited on a Cu substrate with 0.5 and 1 µm thicknesses. The samples were stored in room ...conditions (22 ± 1 °C/50 ± 5RH%) for 60 days. The Sn whiskers and the Cu–Sn layer structure underneath them were investigated with both scanning electron and ion microscopy. Fast Cu–Sn intermetallic formation resulted in considerable mechanical stress in the Sn layer, which initiated intensive whisker growth right after the layer deposition. The thinner Sn layer produced twice many whiskers compared to the thicker one. The lengths of the filament-type whiskers were similar, but the growth characteristics differed. The thinner Sn layer performed the highest whisker growth rates during the first 7 days, while the thicker Sn layer increased the growth rate only after 7 days. This phenomenon was explained by the cross-correlation of the stress relaxation ability of Sn layers and the amount of Sn atoms for whisker growth. The very high filament whisker growth rates might be caused by the interface flow mechanism, which could be initiated by the intermetallic layer growth itself. Furthermore, a correlation was found between the type of the whiskers and the morphology of the intermetallic layer underneath.
•Risk of the component displacement failure during the Vapour Phase Soldering (VPS) was analysed.•A 3D computational fluid dynamic model of the VPS process was established.•Condensate layer formation ...around large-size components during VPS was investigated.•Onset differences in the melting of the solder alloy at the opposite leads of the component were calculated.•Keep-out zones on the board were suggested to reduce the component displacement failures.
The reflow soldering process of large size components was always problematic in microelectronics manufacturing due to the possibility of component displacement failures after soldering; like tombstone formation or skewing, which can be traced back to the different heating of the opposite component sides. During vapour phase soldering, the efficiency of heat transfer highly depends on the thickness of the condensate layer. In this paper, the inhomogeneity of condensate layer formation and its effects were investigated at large size components during vapour phase soldering by numerical simulations. For this purpose, a 3D computational fluid dynamic model was established. According to the condensate layer formation in different cases, the onset differences in the melting of the solder alloy at the opposite leads of the component were calculated. By the results, the risk of the component displacement during reflow soldering was analysed. It was found, that the congestion of the condensate layer around the large size components can cause considerable differences in the onset of the solder alloy melting, which can yield in component displacement failures after soldering. The extent of difference in the onset of melting depends on the location of the component on the board and on the applied soak temperature. Keep-out zones on the board were suggested to reduce the possibility of the component displacement failures during the vapour phase soldering process.
•The electrochemical migration is investigated on micro-alloyed low Ag solders.•Transmission electron microscopy is applied to investigate dendrites.•Antimony (micro-alloy) takes part during ...electrochemical migration processes.•The electrochemical migration model of antimony is established.
The Electrochemical Migration (ECM) behaviour of lead-free, micro-alloyed, low Ag solder alloys was investigated using Scanning Transmission Electron Microscopy (STEM), Energy Disperse X-ray Spectroscopy (EDS) and electron diffraction methods. Different solder alloys were investigated by Water Drop (WD) tests to stimulate ECM failure mechanism. After WD tests, differently structured dendrites were formed depending on the solder alloy types. The results showed that micro-alloying components (e.g. Sb) also played role during the ECM processes. The novelty of this study is the demonstration that Sb can take part in the ECM process; the ECM model of Sb is also discussed.
In this paper, we introduce an automated Bayesian visual inspection framework for printed circuit board (PCB) assemblies, which is able to simultaneously deal with various shaped circuit elements ...(CEs) on multiple scales. We propose a novel hierarchical multi-marked point process model for this purpose and demonstrate its efficiency on the task of solder paste scooping detection and scoop area estimation, which are important factors regarding the strength of the joints. A global optimization process attempts to find the optimal configuration of circuit entities, considering the observed image data, prior knowledge, and interactions between the neighboring CEs. The computational requirements are kept tractable by a data-driven stochastic entity generation scheme. The proposed method is evaluated on real PCB data sets containing 125 images with more than 10 000 splice entities.
In this paper, a new explicit state variable was introduced which describes the Ag
3
Sn intermetallic morphology inside of lead-free solder joints at different cooling rates. In the experiment, ...samples were prepared by melting standard Ag-content (4 % in wt%) and low Ag-content (0.3 % in wt%) solder alloys, and solidifying them at five different cooling rates between 0.8 and 3 K/s. Images were taken about the cross-section of solder joints by brightfield light-microscope to calculate the explicit state variables, which describe the morphology of precipitating Ag
3
Sn intermetallic compounds. The captured images were processed then with an in-house developed automatic image processing algorithm. It was found that the area of Ag
3
Sn intermetallic compounds followed exponential distribution, so a new state variable could be introduced, such as the amplitude of a certain exponential curve fitted to the area histogram of the Ag
3
Sn IMCs. It was proven that our new variable described the different Ag
3
Sn IMC morphologies obtained at different cooling rates better; it was more sensitive at both aforementioned solder alloys (4 and 0.3 % Ag content) than the widely applied parameters, like the mean-intercept length or the average area of particles.
Flux contained in solder paste significantly affects the process of solder joint creation during reflow soldering, including the creation of an intermetallic layer (IML). This work investigates the ...dependence of intermetallic layer thickness on ROL0/ROL1 flux classification, glossy or matt solder mask, and OSP/HASL/ENIG soldering pad surface finish. Two original SAC305 solder pastes differing only in the used flux were chosen for the experiment. The influence of multiple reflows was also observed. The intermetallic layer thicknesses were obtained by the image analysis of micro-section images. The flux type proved to have a significant impact on the intermetallic layer thickness. The solder paste with ROL1 caused an increase in IML thickness by up to 40% in comparison to an identical paste with ROL0 flux. Furthermore, doubling the roughness of the solder mask has increased the resulting IML thickness by 37% at HASL surface finish and by an average of 22%.
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