Hot Solder Research Articles

Interfacial structure and properties of anodized 6061 Al alloy joints by ultrasonic-assisted hot dipping and soldering using a Sn–9Zn–2Al filler metal

Al alloy joints soldered with Sn-based filler metal are susceptible to corrosion and early failure when exposed to moisture, resulting in severe accidents and substantial economic losses. This study proposes a method to prevent galvanic corrosion by separating Al alloys and Sn-based filler metals with an insulating barrier layer of anodized aluminum oxide (AAO) composed of Al2O3. The successful joining of anodized aluminum alloy (AAA) with Sn–9Zn–2Al was achieved through ultrasonic-assisted hot dipping and soldering in air at 240 °C. Microstructural examination revealed strong bonding between the solder alloy and AAO, with the solder infiltrating the AAO nanotubes and a transition layer consisting of two sublayers at the interface: amorphous ZnO mixed with nanocrystals (ZnO and Al2O3) and amorphous Al2O3. The shear strength of the joints ranged from 31.8 to 32.8 MPa when subjected to ultrasonic hot dipping for 0.5–2.0 s, with no significant difference observed. Fracture initiation and propagation occur within the transition layer at the interface. The shear strength of joints subjected to dipping for more than 3.0 s decreased slightly to 27.9 MPa due to localized peeling off of AAO from the Al substrate. The formation of the interface involves the segregation of Al and Zn on the liquid filler metal surface, driven by differences in atomic activity. Due to the jet force from cavitation, an Al-rich liquid infiltrates the nanotube, resulting in the formation of Zn–O at the interface and Al–O both at the interface and within the nanotube. Throughout this process, the wetting model shifts from a Cassie state to a near-Wenzel state. Immersion tests of two types of joints, Al/SnZnAl/Al and AAA/SnZnAl/AAA, confirmed that galvanic corrosion of Sn/Al was completely inhibited by the latter. Consequently, AAA joints demonstrate excellent corrosion resistance, validating this approach as a promising solution to the Al/Sn galvanic corrosion issue.

Impact of hot air gun soldering process parameters on the electromechanical properties of electronic yarn

Researchers now confirm that the market for electronic textiles, or ‘E-textiles,’ will rise rapidly. One method of creating e-textiles is the integration of electronics with textiles. Several techniques were used to combine electronics with conductive textile. One of the best methods for connecting electronics to conductive textile fabrics is soldering. Because of this, it is important to look into how the soldering process parameter affects the developed e-textile’s characteristics. In the research paper presented, the effects of temperature, speed of hot air, and amount of paste size of hot air gun re-flow soldering parameters on the electromechanical properties of surface mount device (SMD) embedded electronic yarn were examined. Three main soldering parameters at four different levels were selected based on the preliminary test results involving the soldering of the tiny SMD into CLEVERTEX electrically conductive hybrid yarn. The result shows that soldering of SMD into CLEVERTEX electrically conductive hybrid yarn provided a higher conductivity with 10-ohm DC resistance. Statistical analyses were also carried out to prove the significant effect of the temperature on changing electrical resistance at, α = 0.5, with an F-value of 0.27 and a p value of .036. While the effects of different amounts of solder paste size on the electrical resistance were not statistically significant at α = 0.5, with an F-value of 0.27 and a p value of .84. Moreover, the tensile strength of the developed e-yarn was affected by the hot air soldering parameters. Furthermore, the developments of e-yarn using hot air gun soldering was pronounced in more extreme process conditions, which revealed that there was a strong interaction between the solder temperature, solder paste volume and solder speed. Furthermore, this approach made it easier to generate the optimum quality of e-yarn needed to continue creating prototype electronic textiles.

Inexpensive Fabrication of Sn-Ag- Cu/Cu:ZnO/Al/PET Memristive Devices through Unconventional Synthesis Techniques

In the last few decades there has been rapidly growing research interest in resistive switching devices which led to tremendous technological advancements. In this work, copper (Cu) doped zinc oxide (ZnO) thin film was deposited on Aluminum coated PET conductive sheets having a sheet resistance of 20 Ω. Soldering balls of 2 mm diameter consisting of 96.5% Sn, 3% Ag and 0.5% Cu alloy were dropped into this thin film to form the Sn-Ag- Cu/Cu:ZnO/Al/PET memristive devices. No additional annealing temperature was required as the heat transfer from 350 C hot soldering ball onto the Cu:ZnO thin film was sufficient to anneal the thin film. The electronic characteristics of the device were obtained by employing a function generator and an oscilloscope instead of an expensive source meter. The elimination of redundant hot furnace (for annealing) and source meter (for I-V characterization) resulted in the improvement of total equipment expenses by ~96%.

Bonding Property of Middle Temperature Sn-Ag-Cu Solder Ball Joint of Ball Grid Array Package

Alloying effects of Nickel and Bismuth in SAC solder to achieve mechanical and microstructural evolution were investigated by comparing three different chemical composition of solders. Sn-3.0Ag-0.5Cu (SAC305) is the most commonly used for Pb-free solder and solder balls are based on Sn-Ag-Cu alloy composition. Compositions of solder balls were Sn-3.0Ag-0.5Cu (SAC305), Sn-1.2Ag-0.5Cu-0.05Ni (SAC1205N) and Sn-Ag-Cu-Ni-Bi based solder (SACNB). Organic solderability preservative (OSP) surface finished substrate, ball grid array (BGA) package arranged by 300 ㎛ diameter solder ball and Type 4 solder paste were used. Solder ball shear test of the BGA package was conducted before the reflow soldering. Board level package bonding process was carried out by hot air reflow soldering. Void content of the BGA solder joint was investigated after soldering. The microstructure evolution before and after thermal cycle test (TCT) was observed using scanning eletron microscopy (SEM) and energy dispersive spectroscopy (EDS). After TCT, intermetallic compound (IMC) refinement and solid solution strengthening effects of Bi element addition were observed in the solder matrix, and also any segregation of Bi element was not founded. Based on these result, it was found that the solder joint reliability of the middle and low temperature solder joints was improved.

Bonding Property of Flip-Chip Chip-Scale Package with Vacuum Reflow and Thermal Compression Bonding Processes

The package-on-package technology has been developed to facilitate high-density integration of semiconductor packaging. As the solder bump pitch is decreased, the void content in solder bump joints increases, thereby decreasing its reliability. Consequently, vacuum reflow (VR) is used to increase void fluidity and decrease void content in micro bump joints. Generally, silicon chips in application processor modules are bonded using thermal compression (TC) bonding, followed by the attachment of passive components through hot air reflow soldering. However, the simultaneous bonding of Si chips and passive components using VR can improve productivity.In this study, we performed TC and VR bonding without additional solder pastes, between an Si chip with a Cu pillar/Sn-2.5Ag bump and a bismaleimide triazine substrate plated with electroless-nickel electroless-palladium immersion-gold. It was observed that the void content at the Si chip solder joints yielded by VR (10.8%) was similar to that yielded by TC (11.2%). Furthermore, the Si chip solder joint of the VR sample was thicker than that of the TC sample. This process also resulted in the formation of the intermetallic compounds Cu<sub>6</sub>Sn<sub>5</sub>, (Cu,Ni)<sub>6</sub>Sn<sub>5</sub>, Ag<sub>3</sub>Sn, and Ni<sub>3</sub>P, at the Si chip solder joints. The results of this study suggest that co-bonding of active and passive components is possible through VR soldering for semiconductor packaging.

Optimization Method for Hot Air Reflow Soldering Process Based on Robust Design

The process design of hot air reflow soldering is one of the key factors affecting the quality of PCBA (Printed Circuit Board Assembly) component products. In order to improve the product quality during the design process, this paper proposes a robust optimization-based finite element simulation analysis method including significant influencing factor screening, robustness evaluation, robust optimization, and reliability verification for the reflow soldering process. The simulation model of the reflow soldering process temperature field based on experiments is constructed and validated. Sensitivity analysis is used to select important influencing factors, such as the last five set temperature zones (T5 to T9) in the reflow oven and the thermal properties of materials such as PCBs (printed circuit boards), BGAs (ball grid arrays), and solder paste, as well as noise factors like the heating environment during the soldering process. Several surrogate models are used to construct the response surface, and the optimal fitting scheme is selected to effectively avoid poor fitting caused by inappropriate surrogate models. The 6σ robust optimization approach is introduced to evaluate and optimize the robustness of the process design parameter where the heating factor is chosen as the optimization target. The reliability analysis method is employed to validate the product quality. This paper establishes a comprehensive robustness analysis method for hot air reflow soldering, effectively reducing design costs and addressing the lack of robustness analysis in the current hot air reflow soldering process design.

Interfacial Properties of Sn-Cu-xCr Alloy using Laser-Assisted Bonding

Conventional hot air reflow soldering is one of major bonding technology when bonding is proceeded on automotive electronics applications. However, here we focus on modifying the bonding process and composition of solder to enhance mechanical and thermal properties. This study experimentally investigated the mechanism of how laser-assisted bonding (LAB) form a small size of initial intermetallic compounds (IMC), and 0.2 wt% Cr element was added to Sn-0.7Cu eutectic solder to suppress the IMC growth. As a result, Sn-0.7Cu and Sn-0.7Cu-0.2Cr initial grain refinement was achieved by LAB. Isothermal aging was conducted to observe the mechanical and thermal properties depending on the IMC growth under 100, 125, 150 ℃ respectively. Sn-0.7Cu-0.2Cr tended to inhibit the growth of IMC at solder matrix and interface compared to Sn-0.7Cu throughout all aging temperature and time. The shear test was proceeded and Sn-0.7Cu-0.2Cr shear force was achieved 18% higher than Sn-0.7Cu. Even after isothermal aging, Sn-0.7Cu-0.2Cr showed lower reduction rate of shear force compared to Sn-0.7Cu.

Solder Joint Degradation and Electrochemical Metallic Ion Migration Property of Solder Joints with Surface Finish

To confirm the degradation property of solder joints by substrate surface finish, chip resistors are reflow soldered to organic solderability preservative (OSP) and electroless nickel immersion gold (ENIG) finish substrate in a nitrogen atmosphere using the type 6 Sn-3.0Ag-0.5Cu (SAC305) solder paste. To confirm the electrochemical metallic ion migration (ECM) sensitivity with and without photo solder resist (PSR) ink-coated printed circuit board (PCB), comb patterned test vehicles were prepared by the hot air reflow soldering process in nitrogen atmosphere, and the SAC305 solder paste was printed on the conductor of the ECM test PCB. The ECM test was conducted under high temperature and high humidity conditions of 85℃ and 85% RH, respectively. As a result of measuring the void content of the 2012 chip resistor, the average void content of the OSP substrate was higher than that of the ENIG substrate. The thermal shock test (TST) indicated that the degradation rate of the OSP substrate was higher than that of the ENIG substrate. Microstructure analysis showed that the OSP substrate had more crack propagation and thicker intermetallic compound (IMC) thickness than the ENIG substrate. The ECM test revealed that the substrate with PSR-coated PCB coupon generated more dendrites than that without PSR-coated coupon. Because the PSR coated substrate decreased the moisture absorption into the substrate, moredendritesweredeterminedtobe generated.

Assembling and Testing of a Microcontroller Based Smart System Suitable for Controlling Brushless Fan

This research focuses on testing and assembling of a microcontroller based smart system suitable for controlling brushless fan that will detect temperature in a room, maintain and adjusts a speed of a cooling fan. The automation system comprises of Arduino Uno board, Microcontroller, temperature sensor, DC brushless motor and other electronics components. The Atmega328P-PU Microcontroller was used in programming the system, the microcontroller coordinates the functions of the entire system and the Pulse Width Modulation (PWM) signals from the microcontroller served as regulatory tools to the fan. All the components were tested and gave out the desired result. Potentiometer was used initially before placing the LM35 temperature sensor by using hot soldering iron which corresponds with voltage values between 0-5V on Multimeter reading and 5 to 254 serial monitor reading by varying the duty cycle 0 to 100 with approximately 500Hz frequency. Six different temperature values were obtained from the circuit by varying the LM35 temperature sensor and responds to the amount of heat supplied which regulate the cooling fan on regular basis. The current temperature values displayed on LCD screen, also the aimed of the work has achieved

Optimization of FC-CSP and MLCC Soldering Process Using Type 7 Solder Paste

To confirm the possibility of simultaneous bonding between Si chip and multilayer ceramic capacitors (MLCCs), vacuum reflow soldering is performed between a Si chip and each of 2012, 1608, 1005, 0603, and 0402 MLCCs using Type-7 Sn-3.0Ag-0.5Cu (SAC305) and Sn-0.7Cu solder pastes. To enable an unbiased comparison with the vacuum reflow process, the Si chip and MLCCs are bonded via thermo-compression (TC) bonding and hot air reflow soldering, respectively. The maximum void content of Si chip solder joints bonded via vacuum reflow is 8%. At the MLCC solder joints, the void content yielded by vacuum reflow is lower than that yielded by hot air reflow. The bonding strength of the MLCC solder joint afforded by vacuum reflow is higher than that afforded by hot air reflow. Vacuum reflow is superior to hot air reflow in terms of the void content and bonding strength of the MLCC solder joint. After performing a thermal cycle test (TCT), a crack appeared at the Si chip solder joint bonded by TC bonding. The Cu pillar/Sn-2.5Ag bump is susceptible to cracks after the TCT owing to the insufficient bonding layer thickness yielded; however, the SAC305 sample from vacuum reflow is stable. Meanwhile, (Cu,Ni)6Sn5, Ni3P, and Ag3Sn intermetallic compounds are formed at the MLCC solder joints and then further developed after the TCT. The results of this study indicate the possibility of co-bonding Si chip with MLCCs for semiconductor packaging.

MLCC Solder Joint Property with Vacuum and Hot Air Reflow Soldering Processes

After the joining of small 1005 and 0603 multilayer ceramic capacitor (MLCC) components for a semiconductor package using Type 4 (T4) and Type 7 (T7) Sn-3.0Ag-0.5Cu (SAC305), T4 Sn-1.0Ag-0.5Cu (SAC105), and T4 Sn-0.3Ag-0.7Cu (SAC0307) solder pastes, the differences between hot air reflow and vacuum soldering processes were compared in terms of void content, shear strength, and microstructure. Results showed that the hot air reflow soldering process exhibited a stable joint with a void content of 5% or less, and the vacuum soldering condition significantly reduced the void content of the solder joint as the soldering proceeded in a vacuum state. The shear strength of the SAC305 solder joint with the same powder particle size was measured to be greater for the shear strength of the vacuum soldered joint as compared to the reflow process. The vacuum soldering process was effective in removing voids during the void joining process and contributed to an improved joint strength of the solder joint by reducing the void content. When the same soldering process was applied using the 1005 MLCC chip component, the bonding strength of the T4 SAC305 solder was slightly higher than those of the SAC105 and SAC0307 solders. However, the overall initial bonding strengths were similar. The e ffects of Ag content within 0.3-3.0 wt% on the initial bonding strengths of the solders were judged to be the same. Diverse Cu6Sn5, Ag3Sn, (Ni,Cu,Pd)3Sn4, (Cu,Ni)6Sn5, NiP, and Ni3P intermetalli ccompounds (IMCs) were formed at the interfaces between the electroless nickel/electroless palladium/immersion gold finish substrate and SAC solder joint. The IMC types were constant regardless of Ag content and solder type, and the IMCs contributed to the initial solder joint strength.

Research on temperature field model of hot air reflow soldering process

In this paper, two typical temperature models on the hot air reflow soldering process are studied. The critical difference between the two model is the approach used to compute the convective heat trans coefficient during the soldering process. In the model 1, the Martin formula and k-epsilon (2eqn) equation is applied to obtain the average convective heat transfer coefficient. And in model 2, the liquid and solid coupling CFD model is built to compute the convective heat transfer coefficient inherently. The comparing between the simulation and the test is conducted and shows that the simulation result of model 2 are closer to the real value. The comparing between these two models shows that the gas temperature, the gas velocity and the convective heat transfer coefficient around the PCBA is quite different. It is indicated that the average convective heat transfer coefficient calculated by Martin formula was larger. The CFD model is prefer for simulating the temperature distribution of the PCBA during the air reflow soldering when higher result precision is needed.

Convolutional neural network model for synchrotron radiation imaging datasets to automatically detect interfacial microstructure: An in situ process monitoring tool during solar PV ribbon fabrication

Designing means and methods to detect the presence of interfacial bubbles and intermetallic compounds (IMCs) during hot dipping solder coating of Cu ribbon, can help in the production of defect-free PV ribbons. A mechanistic study of Cu6Sn5 IMC grain growth and bubble morphology evolution at the solder-substrate interface is performed with phase field simulation. A machine learning model is utilized to identify the occurrence of bubble(s) and IMC at the material interface of liquid solder and solid Cu. The datasets for the microstructural images consisting of bubble(s), IMC and planar solder/Cu interface are generated using in situ synchrotron radiation (SR) imaging experiment techniques. The integration of in situ SR radiography based non-destructive testing experiments with convolutional neural network model to intelligently detect the interfacial microstructures paves the path for potential industrial application of this technique in the smart manufacturing of defect free and reliable PV ribbon material.

Instrumentation of Twin-MCMs based mutual-test

This paper presents advanced data collection methods using boundary scan based vector analysis, developed to debug manufacturing defects on cell based IC's such as JTAG compliant dice. Advantageously, they provide solutions to unknown dice by arranging identically designed Multi-chip Modules (MCM), to thereby diagnose possible flaws on dice due to thermal stresses on substrates as well as cold or hot soldering of the bumps, of which introducing fatigue and cracks, etc., defectives, and this system potentially to repair the problematic MCMs after trouble-shooting the twin-MCMs through self and mutual testing to validate the Known Good Dice (KGD).

Research on the Influence of Device Thermal Equivalent Model on the Temperature Field of Infrared Hot Air Reflow Soldering

Infrared hot air reflow soldering is an important process in SMT assembly process. The temperature field of infrared hot air reflow soldering of PCBA will directly affect the reliability of solder joints. The different simplified equivalent models have a certain influence on the temperature field of infrared hot air reflow soldering PCBA, which is mainly reflected in accuracy and efficiency. This paper studies the influence of three different thermal models on the temperature field of reflow soldering PCBA, and selects four groups of points in the same position of the three models, and comprehensively compares their temperatures. The results show that the maximum temperature deviation of the three models is as high as 7℃ in the soldering zone and 4℃ in the cooling zone, and the temperature difference is small. It can be concluded that the complex solder ball model can be used for high precision applications, and the simplified single-layer solder model and the thermal equivalent model can be used for low precision applications. These conclusions provide some references for the modeling of infrared hot air reflow soldering.

Thermoset Polymer Splicing Study Using a variation of welding

There is not much plastic welding currently done and not much research has been done on plastic welding. The purpose of this study was to study the use of welding variations used to join the thermoset polymer material. The thermoset polymer materials used are acrylic, melamine and bakelit with the test sample measuring 80mm in length, 30mm in width and 3mm in thickness. Variations in welding are used using hot gas welding, electric soldering and gas torches. The test method is carried out after welding to determine the porosity of the weld using a penetrant liquid. Hardness testing was also carried out. The best welding results are shown on acrylic material using electric solder, showing that the amount of porosity is the least, and has the highest hardness test.

Study on Influencing Factors and Laws of Temperature Field Distribution of Infrared Hot Air Reflow Soldering

The quality of solder joints formed by reflow soldering is closely related to the temperature profile of solder joint during the hot air reflow soldering process. The temperature profile of solder joint is directly determined by the process parameters of the reflow furnace as the layout of the PCB design remains same. In this paper, the temperature model of the printed board assembly during reflow soldering is numerically built and simulated to obtain the temperature distribution. Furtherly, several process parameters, such as the temperature of each temperature zone, convective heat transfer coefficient and conveyor belt speed of reflow soldering furnace, are selected as the input variables, and the heating factor, time of super liquidus and peak temperature are aimed as the output parameters. The Latin hypercube sampling design is applied to construct the response surface of the output parameters. The influence of these process parameters during the reflow soldering on the temperature profile of PCBA is studied comprehensively. The main influencing process parameters of the reflow soldering are identified and their influence laws are obtained. The research results provide valuable reference and basis for reflow soldering process design.

Experimental and Modeling Study on Delamination Risks for Refinished Electronic Packages Under Hot Solder Dip Loads

For electronic packaging engineers in the high-reliability sectors, such as aerospace, defense, oil & gas, etc., the use of commercial off-the-shelf components offers significant advantages due to their high availability, fast delivery time, and low cost. However, these components pose significant reliability challenges due to the risks associated with tin whisker formation and uncertainty on the long-term reliability of lead-free solders. For addressing these risks, the hot solder dip process is used to refinish the package by replacing lead-free solder finishes with lead-based finishes to meet the stringent packaging and assembly requirements for these sectors, which are exempt from restriction of hazardous substances (RoHS) legislation. But the hot solder dip process is an extra process that exposes the package to an additional thermal load, which will result in thermomechanical stresses that need to be properly understood and controlled. For addressing this challenge, a multidisciplinary methodology combining thermomechanical models with “dip-to-destroy” experiments and scanning acoustic microscopy has been developed to identify the risk of package material delamination for a number of package designs. Results show that the developed models can predict delamination risks for a range of imposed thermal gradients. Electronic package designs with a direct heat path from dipped terminations to the internals of the package show a higher risk of overstress-induced delamination, and this failure is generally driven by the high-temperature excursion above the glass transition point of the molding compound. The novelty and significance of these findings is that the derived methodology can be used by electronic packaging designers to optimize the thermal parameters of the hot-solder-dip process so that subsequent refinished packages can meet the stringent high-reliability requirements for these sectors.

Analysis of Hot Bar Soldering, Insulation Displacement Connections (IDC), and Anisotropic Conductive Adhesives (ACA), for the Automated Production of Smart Textiles.

Despite all the growth forecasts of the smart textiles market, there is no stable automated manufacturing process for attaching classic electronics to textiles. The great amount of manual production steps causes high prices, which slow down market growth. During the production process, the contacting step offers the greatest potential to reduce manual manufacturing steps. For this reason, we have analyzed various contacting methods for electronic parts on conductive yarns that have a high potential for automation. The chosen methods were thermode soldering, insulation–displacement connectors and anisotropic conductive adhesives. In order to ensure reliable mechanical contacting, the samples were tested in a peeling experiment. The examination of the contact resistances took place in the context of a resistance test using four-wire measuring technology.

Temperature Measurement of Fluid Flows by Using a Focusing Schlieren Method.

A method for measuring planar temperature fields of fluid flows is proposed. The focusing schlieren technique together with a calibration procedure to fulfill such a purpose is used. The focusing schlieren technique uses an off-axis circular illumination to reduce the depth of focus of the optical system. The calibration procedure is based on the relation of the intensity level of each pixel of a focused schlieren image to the corresponding cutoff grid position measured at the exit focal plane of the schlieren lens. The method is applied to measure planar temperature fields of the hot air issuing from a 10 mm diameter nozzle of a commercial Hot Air Gun Soldering Station Welding. Our tests are carried out at different temperature values and different planes along the radial position of the nozzle of the hot air. The experimental values of temperature measurements are in agree with those measured using a thermocouple.