Jonáš Uřičář

The paper investigates the effect of isothermal curing profiles, based on detailed kinetic analysis, on the mechanical, thermomechanical, and microstructural properties of an epoxy composite microelectronic packaging underfill material for enhanced electronics reliability. Five isothermal profiles were developed based on detailed Kamal-Sourour kinetic modelling to achieve near-complete curing. Subsequent characterisation included DSC, tensile tests, DMA, microhardness measurements, and SEM-EDS analysis. The results revealed a complex dependence of properties on the curing profile. The 170 °C profile provided the optimal ultimate tensile strength (UTS≈71.5 MPa) and Young’s modulus (5.53 GPa), which correlated with the most homogeneous polymer network as determined by the narrowest glass transition width. Conversely, Tg values exhibited a strong inverse relationship with UTS and Young’s modulus, qualified by strong negative Spearman correlations (−1.0 to −0.9). The 150 °C profile resulted in the highest toughness. The microstructural analysis confirmed SiO2 filler sedimentation at 110 °C, while profiles at 150–170 °C showed the most uniform filler distribution. The thermal degradation of the material was observed at the 190 °C profile. The study demonstrates that the specific temperature–time profile, not just the achieved degree of cure, critically dictates the underfill’s microstructure and final properties. Identification of the optimal process window, approximately 150–170 °C for this material, is essential for achieving desired performance while minimising defects, a fundamental aspect of reliability in electronic applications. Furthermore, this defined processing window provides the flexibility to adapt curing profiles to the thermal constraints of a component or assembly, helping to mitigate thermomechanical stress during manufacturing.

Stereolithography, as one of the most common 3D printing methods today, can be utilized to advantage the production of complex shapes of functional materials for many applications in electronics. By mixing additives (mostly in powder form) and photopolymer resin, printable materials with specific properties can be prepared: conductors, magnetics, insulators, or dielectrics. This work deals with a novel ceramic composite based on barium titanate(IV). In the experimental part, five different resins (with 0, 5, 10, 15 and 20 wt.% of filler) were prepared and used for the 3D printing of test samples for subsequent characterization: thermal, mechanical, and electrical properties. The dielectric spectroscopy showed that the relative permittivity increased by 89 % against the pure resin for the maximum filling ratio (to εr = 7.96 at 1 kHz, 30 °C), and the increase was significantly higher for elevated temperatures (from εr = 4.70 up to 10.83 at 1 kHz, 60 °C). On the other hand, the material exhibited a decrease in glass transition temperature, and the mechanical properties deteriorated with increasing filler content. Although further improvement is inevitable, the developed material could find a place in a special electronics application like printable dielectric material, e.g., for printing capacitors, dielectric resonation antennas, or functionally graded structures for high-voltage applications. The main advantage is the maintained easy printability and simple preparation method of the composite.

Lithium is crucial in lithium-ion batteries (LIBs), serving as a main component of the electrolyte and cathode. Elements such as cobalt, nickel, and manganese are also vital for high performance, energy density, and stability. This study aimed to examine the behaviour of end-of-life cathode material (LiNi0.6Mn0.2Co0.2O2) and its valuable metals after exposure to temperatures between 100 and 400 °C, comparing it with untreated material. The lithium content cannot be reliably determined by conventional analytical methods, so inductively coupled plasma optical emission spectroscopy (ICP-OES) was chosen for this purpose. For ICP-OES measurements, samples were dissolved in different solvents for a specified time, and the concentrations of lithium, nickel, manganese, and cobalt were measured. From the measured values, their theoretical yields were calculated. Due to the annealing at given temperatures and subsequent dissolution, this step can be considered as the first stage of the pyrometallurgical-hydrometallurgical process used in battery recycling. The study was complemented by further analyses to monitor the effect of annealing temperatures on the properties of the material. Based on the results, it was found that the highest theoretical yield in this temperature range was for material annealed at 400 °C and dissolved in 20 % nitric acid for 4 h.

The objective of this work was to modify a commercially available 3D printer with a syringe extrusion system inspired by clay 3D printing systems and, afterward, to print conductive test samples from prepared pastes. The pastes were prepared by dissolving polystyrene insulation foam in acetone and adding electrically conductive graphite powder in various loadings. The pastes were homogenized by ultrasonication. Subsequently, the test samples were printed and rested overnight for evaporation of the acetone solvent. Cuboid samples were used for the measurement of the sheet resistance and volume resistivity, followed by analyses of thermal properties and microscopy. The samples containing 23 wt.% and 33 wt.% of graphite exhibited a significantly increased electrical conductivity. Benefiting from a simple preparation, these materials, in conjunction with modified syringe-based 3D printing, can be used in many applications where electrical conductivity is required, such as electromagnetic shielding or sensors.

Two types of solder paste, where for each there were three production / expiry dates, were compared on a gas chromatography and evaluated in terms of their application using stencil printing on a copper substrate (OSP surface finish). The number, percentage, and number of macrovoids were evaluated and compared. Altogether, six solder paste samples were tested, for each solder paste, the voids were evaluated using X-ray spectroscopy on 14 pads with a 1206 pad size. Despite the results from the gas chromatography showed the effect of solder paste aging, the voiding of the pastes did not differ significantly and, on the contrary, the percentage representation of voids was the smallest with the oldest solder paste.

The aim of this work was to evaluate the effect of 0.1 wt.% titanium dioxide nanoparticles (NPs) incorporated in low-temperature Bi58Sn42 solder paste on spreading behavior and mechanical and thermal properties. The spreading test was conducted on testing printed circuit boards with an Organic Solderability Preservative (OSP) surface protection of copper layer. Mechanical properties were evaluated by a shear strength test of 1206 resistors soldered on FR4 boards with OSP coating. Shear strength was also studied in dependence on accelerated thermal aging. The prepared test boards for the shear test were annealed in a climatic chamber at 85°C and 100°C for 1000 hours. Additionally, the solder alloys were subjected to Differential Scanning Calorimetry (DSC) to examine their thermal properties. The results showed a significant improvement in spreading when using solder paste with incorporated TiO2 NPs. Furthermore, TiO2 nanoparticles did not prominently deteriorate the thermal and mechanical properties.

Due to electronics miniaturization, the size of voids is becoming comparable to that of solder joints, thereby increasing the risk of reduced reliability. This work presents a novel method of achieving void reduction through preliminary characterization of the flux and, consequently, the proper flux selection and adjustment of the temperature profile during soldering. To validate this approach, five SAC305 solder pastes differing in flux composition were subjected to testing. The flux components were characterized by a gas chromatograph combined with a mass spectrometer (GC–MS) and thermogravimetric analysis (TGA). Subsequently, four temperature profiles differing in the heating rate were employed for reflow soldering of the test boards with components while maintaining the same peak temperature for all profiles. The results of the X-ray computed tomography (XCT) analysis indicated that as the temperature gradient decreased, the number of voids decreased by up to 36%. The decrease in the number of flux residues detected by TGA present at the peak process temperature was also accompanied by a decrease in the void area within the solder joint. Moreover, a comparison between the GC–MS and XCT results revealed that certain flux compounds, such as butylated hydroxytoluene, were found to have a greater impact on void formation than others. The proposed method combining flux characterization by GC–MS and TGA and adjustment of temperature gradient during the soldering process can be an efficient way to reduce voids in solder joints. Additionally, it appears that a lower temperature gradient is generally associated with a lower incidence of voids.

It is well known that the reflow temperature profile has an influence on the thickness of intermetallic layers. The higher the thermal treatment, especially above the melting temperature of solder alloy, the higher the thickness of intermetallic layers. The heating factor (time-temperature integral of temperature profile above the melting temperature) is commonly used for comparison of the heat treatment. This paper deals with a comparison of three different reflow temperature profiles (with three different heating factors: 242, 1061 and 1652 s.K), three surface finishes (Organic Solderability Preservative - OSP, Hot Air Solder Leveling - HASL and Electroless Nickel Immersion Gold - ENIG) of copper soldering pads and two solder pastes with the same composition of solder alloy (Sn96,5/Ag3,0/Cu0,5) but with different flux type (less aggressive - ROL0 and more aggressive - ROL1). The cross-sections of the samples were prepared after the reflow soldering process, followed by analysis by scanning electron microscope and measurement of intermetallic layers thicknesses. Results confirmed that the heating factor significantly influences the intermetallic layers. The highest thickness of intermetallic layers was achieved with the highest value of the heating factor. The surface finish HASL had the highest values of intermetallic layer thicknesses from all used surface finishes, whereas ENIG had the lowest. The higher values of intermetallic layer thickness were observed for the solder paste with a more aggressive flux, ROL1, than for ROL0.

Recycling lithium-ion batteries (LIBs) is crucial for environmental sustainability and resource conservation. However, current recycling procedures, particularly for smaller battery formats, pose several challenges. With the increasing demands of the circular economy for LIB waste treatment, it is essential to identify and address obstacles associated with concurrent processes. Thus, this study focuses on characterizing and examining the dilemmas of electrochemical discharging of cylindrical LIB cells. It primarily examines the quantity and composition of released battery mass from nickel-aluminium-cobalt (NCA) LIB cells using aqueous discharging via solutions of sodium chloride (NaCl), sodium hydroxide (NaOH), and sodium nitrate (NaNO3) within the 5-30 wt. % range. Additionally, the work monitored several procedure parameters, including the voltage profiles during discharging, the extent of battery contacts and casing damage after discharging, the character and material composition of the obtained battery mass, and the composition of the wastewater obtained after separating the solid product from waste solutions. Consequently, it was determined that the industrial implementation of these procedures, including material leakage and disposal, may incur economic losses of up to 1560 USD/tonne due to metal loss.

To enhance the solderability, highly active fluxes are commonly employed in lead-free soldering. However, there are industry-wide efforts to use less active fluxes to avoid possible issues associated with corrosion processes and minimize subsequent cleaning processes, thereby reducing potential environmentally harmful waste. Therefore, in this study, the effect of the plasma treatment (N2/H2 97:3) on the wettability of the soldered surface (copper connectors) was investigated. Wettability measurements were conducted using SAC305 solder alloy and six different fluxes. The wetting balance test revealed a significant improvement in wetting for all tested fluxes, regardless of their composition. On the other hand, non-wetting occurred when no flux was applied to the plasma-treated surface, attributed to a thin residual oxide layer detected by X-ray photoelectron spectroscopy. Thus, the plasma treatment of the surface supports the flux effect, which cannot be entirely omitted from the soldering process. However, incorporating plasma treatment in the soldering process allows for the use of much less active or even expired fluxes.

3D printing is an extensively used manufacturing technique that can pose specific health concerns due to the emission of volatile organic compounds (VOC). Herein, a detailed characterization of 3D printing-related VOC using solid-phase microextraction-gas chromatography/mass spectrometry (SPME-GC/MS) is described for the first time. The VOC were extracted in dynamic mode during the printing from the acrylonitrile-styrene-acrylate filament in an environmental chamber. The effect of extraction time on the extraction efficiency of 16 main VOC was studied for four different commercial SPME arrows. The volatile and semivolatile compounds were the most effectively extracted by carbon wide range-containing and polydimethyl siloxane arrows, respectively. The differences in extraction efficiency between arrows were further correlated to the molecular volume, octanol-water partition coefficient, and vapour pressure of observed VOC. The repeatability of SPME arrows towards the main VOC was assessed from static mode measurements of filament in headspace vials. In addition, we performed a group analysis of 57 VOC clas-sified into 15 categories according to their chemical structure. Divinylbenzene-polydimethyl siloxane ar-row turned out to be a good compromise between the total extracted amount and its distribution among tested VOC. Thus, this arrow was used to demonstrate the usefulness of SPME for the qualification of VOC emitted during printing in a real-life environment. A presented methodology can serve as a fast and reliable method for the qualification and semi-quantification of 3D printing-related VOC.

Poly(vinyl chloride) is widely used in the field of electrical engineering as an insulating material. Its properties are significantly dependent on the content of the plasticisers. In this work we identify plasticisers in commercially available insulated electrical wire. We quantify and qualify released hydrogen chloride and qualify volatile organic compounds at enhanced temperatures by thermogravimetric analysis, potentiometric titration, and gas chromatography-mass spectrometry system. Changes in glass transition temperatures and mechanical properties caused by enhanced temperatures are measured by dynamic mechanical analysis. The data show a significant release of hydrogen chloride above 180 °C, which has a significant effect on the mechanical properties.

The recent expansion of 3D printing caused an increase in requirements of printable materials. Since most materials with sufficient electrical properties are not suitable for 3D printing at home or are financially inaccessible, we seek better alternatives. Here, we report modification of electrical properties of commercially available stereolithography (SLA) photopolymer resin by addition of graphite powder and Fe3O4 nanoparticles. Modified resins were prepared via direct ultrasonication of resin containing up to 5 wt% of fillers. Such resins were immediately used for printing to prevent sedimentation. Printed samples were used for the measurements of DC resistivity, dielectric permittivity, and dielectric loss. The obtained data show promising trends since the resistivity decreased with higher filler content. The increase in dielectric permittivity led to increase in dissipation factor.