Search

This study investigates the backward compatibility solder joint formed at high peak reflow temperature in aerospace industries. The backward compatibility solder joint is made up of lead-free ball grid array mounted on printed circuit board using tin–lead solders at a maximum reflow temperature ranging from 241.9 to 242.45 °C. The reflow process was conducted under a nitrogen atmosphere in a full convection reflow oven for 80.12–81.27 s. The scanning electron microscopy cross section of the solder ball depicts fairly uniform composition and phase distribution of the Pb-free plastic ball grid array and the tin–lead solder paste across all joints. Nanoindentation tests showed better mechanical properties with higher elastic modulus at 68.64 GPa and acceptable hardness value at 0.26 GPa as compared to those of Sn–Pb and Pb-free solder balls. Intermetallic compound formation at both joints seen in the scanning electron microscopy shows a scallop shape and randomly directed growth because of the uniformly distributed Pb-rich phase on the solder ball. The average intermetallic compound thickness measured by scanning electron microscopy equipped with energy-dispersive X-ray analysis was 3.633 μm, which was less than the specified thickness of 12 μm from the laboratory request.

With the high density and high precision requirement of electronic products, printed circuit boards (PCBs) are also facing the evolution into multilayer boards. Electroless nickel immersion gold (ENIG) is a process that is widely used in the surface treatment of PCBs. As a barrier layer, nickel plating is required even in the blind via of PCB to improve its corrosion resistance for further plating processes. In this study, different surfactants, mainly anionic surfactant, Sodium Dodecyl Sulfate (SDS) and cationic surfactant, Cetyl Trimethyl Ammonium Bromide (CTAB), are used to explore their possible effects on this electroless process. It is found that SDS improves the deposition rate in blind via plating and coating's surface roughness. The surfactants are also effective in increasing the corrosion resistance of the prepared coating. Furthermore, different plating processes, i.e. supercritical carbon dioxide (Sc-CO2) assisted electroless plating and post supercritical carbon dioxide assisted electroless plating, are investigated and compared with the conventional process. It is obtained that Sc-CO2 assisted plating has the best improvement in blind via deposition rate and better coating's corrosion resistance. The result is indebted to the fact that the bath mixed with Sc-CO2 has low surface tension of gas and high mass transfusion of liquid. This nature effectively increases the deposition rate of coating in the blind via, and also makes the surface of the coating smoother and more uniform. To further explore whether high temperature affects the corrosion resistance of the coating when it passes through the reflow oven in surface mount technology (SMT) soldering operations of PCB, the coating is annealed at different elevated temperatures up to 400 °C. The experimental results found that annealing enables the grain refinement of the plated layer, thereby enhances the corrosion resistance of the plated layer.

The process of printed circuit board assembly (PCBA) involves several machines, such as a stencil printer, placement machine and reflow oven, to solder and assemble electronic components onto printed circuit boards (PCBs). In the production flow, some failure prevention mechanisms are deployed to ensure the designated quality of PCBA, including solder paste inspection (SPI), automated optical inspection (AOI) and in-circuit testing (ICT). However, such methods to locate the failures are reactive in nature, which may create waste and require additional effort to be spent re-manufacturing and inspecting the PCBs. Worse still, the process performance of the assembly process cannot be guaranteed at a high level. Therefore, there is a need to improve the performance of the PCBA process. To address the aforementioned challenges in the PCBA process, an intelligent assembly process improvement system (IAPIS) is proposed, which integrates the k-means clustering method and multi-response Taguchi method to formulate a pro-active approach to investigate and manage the process performance. The critical process parameters are first identified by means of k-means clustering and the selected parameters are then used to formulate a set of experimental studies by using the multi-response Taguchi method to optimize the performance of the assembly process. To validate the proposed system, a case study of an electronics manufacturer in the solder paste printing process was conducted. The contributions of this study are two-fold: (i) pressure, blade angle and speed are identified as the critical factors in the solder paste printing process; and (ii) a significant improvement in the yield performance of PCBA can be achieved as a component in the smart manufacturing.

Namen diplomske naloge je predstaviti proizvodni proces opremljanja tiskanega vezja. Tiskana vezja danes srečujemo pravzaprav že v čisto vseh elektronskih napravah. Od njih je odvisno, kako bo naprava delovala. Osredotočili smo se na del strojnega polaganja komponent, imenovan SMT oddelek. V tem delu bo predstavljena izdelava programa za tiskanje spajkalne paste na PCB (Printed Board Circuit), sestava spajkalne paste, optični pregled nanosa paste in glavni del polaganja komponent na tiskano vezje. V proizvodnem procesu je bistvenega pomena tudi taljenje spajkalne paste oz. spajkanje SMT komponent, zato smo tudi to tematiko bolj natančno opisali in predstavili. Spoje na tiskanih vezjih je potrebno skrbno pregledati in morebitne napake odpraviti, preden vezje nadaljuje svojo pot po proizvodnji. Za to skrbi AOI (Automated Optical Inspection) operater. Večina tiskanih vezij je sestavljena z uporabo THT (Through Hole Technology) komponent, ki jih potrebujemo za pravilno delovanje tiskanega vezja. Spajkanje teh komponent se opravlja ročno ali z metodo selektivnega spajkanja. Po končani obdelavi tiskanega vezja sledi pregled in čiščenje vezja pred odhodom v odpremo. Na tem mestu se tiskano vezje ustrezno zapakira, da med transportom ne pride do poškodb. The thesis presents the production process of assembling a circuit board. Circuit boards are nowadays found in almost every electrical device. They determine how a certain device will operate. The main focus of the thesis is on the SMT section. In this part we present everything about the development of the program for solder paste printing on PCB, the structure of the solder paste, optical overview of paste deposit and the main part, assembling components on the PCB. We can say, that the main production process is reflowing of the solder paste or soldering SMT components. That is why we have focused mostly on this topic. Special attention needs to be devoted on the PCB joints, in order to find any production faults which need to be resolved before the board moves to further processing. This work is controlled by the AOI operator. The majority of the PCBs are composed with THT components, which are needed for proper functioning of the board. Soldering of the components is carried either manually or using a selective soldering technique. When the PCB is manufactured, final check and cleaning is performed before dispatching. At this point, the PCB is properly packed, in order to avoid any damage during the transport.

The effect of different surface finish with Sn-3.0Ag-0.5Cu (SAC305) solder was successfully investigated. The SAC305 solder was fabricated by using casting method and solder was placed on copper substrate that coated with different surface finish. The soldering process was carried out by using F4N reflow oven followed up with the mounted and metallographic steps. Wettability of SAC305 solder was observed through contact angle formed between solder and four different surface finish located on the copper substrate. Subsequently, the electrical resistivity of solder was studied by conducted the four-point probes. The results of wettability test was found to be in the accepted range which is below 45° for all different surface finish. In terms of electrical resistivity, the results showed that the ImAg surface finish had enhanced the electrical conductivity of SAC305 lead-free solder.

This paper presents a design and realization of a universal reflow oven for both heating and soldering of SMD components, including rebailing of BGA packages. The reflow oven is composed of two blocks in separate housings: a control system and a heating system. The control system was built with the Siemens SIMATIC S7-1200 PLC (programmable logic controller) with additional modules. The heating system consists of a three-zoned thermally isolated heating chamber with an original upper inspection window. Some original solutions were proposed, which significantly facilitated operation of the device. Tests of the reflow oven confirmed relevance of the design assumptions and high quality of the product.

Soldering is very important technology to connect components and printed circuit boards together. Heat is transferred to soldering joint using flow of air or, generally, gas. Heat transfer is depending on more parameters, e.g. distance between product and nozzle field, strength of gas flow. It is very complex issue and not easy to measure. This paper describes some ideas, how to measure gas flow and heat transfer inside of an reflow oven.

For a reflow soldering process, most of the energy consumption is used to heat up the machine itself. If it would be possible to heat up only the solder and pins to the required soldering temperature the energy reduction will be significant. The idea behind such a process is to use a conductive heating material layer inside the printed circuit board (PCB). To generate the joule heating, it is necessary to have an electric current flow through the heating material. The parameters for soldering in a reflow oven are known, but the heating from inside a PCB requires to define new parameters. This paper will describe basic experiments to achieve the necessary process and material parameters like required resistance of the heating layer to obtain a controllable reflow profile for the soldering material. The experiments performed also give boundary conditions for the resulting machine to use this soldering process automatically in a large-scale PCB production environment.

Market is always looking for way to reduce the cost of package. Traditional way of protecting the fragile micro-bumps is by applying capillary underfill (CUF) to mitigate the issue of CTE mismatch between the die and the substrate. However, the use of CUF introduce additional assembly process on top of high material cost as compared to Moldable Underfill (MUF). In this paper, we explore the use of MUF for the 4-diue stack. MUF is very attractive as it combined the step of molding and underfilling into one single step in addition to the low material cost as compared to CUF. The reliability of MUF is much superior to CUF as shown in the simulation study. The simulation study indicates a drastic 1.65 times more fatigue life for MUF as compared to CUF. The 4 die stack is formed using conventional mass reflow process. The dies is stacked on top of each other on a bottom substrate wafer using conventional noclean flux. The whole substrate wafer with the 4 die stack is then send through a reflow oven to form the solder interconnect for all 4 die stacks. This approach is much prefer than individual thermo-compression process in terms of throughput and less thermal loading to the solder interconnects as no heat is applied to each die stacking process. We had demonstrated no void in the region between the solder bump after the MUF molding process.

This study focuses on the onset of plastic flow in different copper as processed materials. The tested copper sheets varied as to how they were manufactured and their post-manufacturing treatments, namely annealing. Tensile tests were conducted at 24 °C, 60 °C, 100 °C, 150 °C inside a temperature controlled test chamber on thin copper specimens. Each material was assessed as received from the manufacturer in its as processed form and after annealing for comparison. Annealing took place for 1 h at 250 °C in a batch reflow soldering oven. The results showed that the onset of plastic flow depends strongly on the manufacturing condition of the copper materials but that the percentage drop-off in flow stress, with respect to operating temperature, is similar for as delivered and annealed copper.

Three dimensional integrated circuit technology has been recently received much interests because it could meet the requirements such as small form factor, high performance, low cost and heterogeneous integration in system-in-package technologies for next generation electronics. For high performance 3D chip stacking, high density interconnections are essential. In the current types of interconnects, solder micro bumps have received much attention due to its low cost in material and process. In this study, two methods of fluxless chip-on-chip bonding process with 30μm pitch lead free solder micro bumps interconnection were demonstrated and the reliability of micro joints was also evaluated. The plasma treatment and the formic acid treatment were used to remove the tin oxidation layer upon the surface of solder micro bumps. The assembly of the chip-on-chip test vehicle with a micro bumps diameter of 18μm and a pitch of 30μm was conducted. There were more than 3000 micro bumps with Sn2.5Ag solder material on both the silicon chip and the silicon carrier. A solder micro bump structure of Cu/SnAg having a thickness of 7μm/15μm was fabricated in silicon chip and the silicon carrier consisted of Cu under bump metallization (UBM) with a thickness of 5μm. During bonding process, the micro joints were formed at pre-bonding and reflowed in reflow oven with a peak temperature of 250 °C. Then, the die shear test was used to check the solder micro joints bonding strength between the silicon chip and carrier by two methods of fluxless process. After bonding process, the microgaps were then filled by a capillary underfill and cured at 165 °C for 2 hours. Reliability tests of temperature cycling test (TCT) and high temperature storage (HTS) were selected to assess the effect of the fluxless bonding process on the reliability of solder micro joints interconnections.

This paper describes the potential impacts of surface mount (SMT) reflow processes on the expected reliability of a Circuit Card Assembly (CCA) and a way to help control those concerns. The impacts can be present as either immediately detectable or latent defects on the CCA. Some defects are easily detected visually while others may take stress screening to fully manifest. Controlling the reflow process will significantly reduce the probability of defects and some can be eliminated completely. A CCA may have only one component to thousands of components. As the component count rises, so does the risk of defects. Other risk factors include the pitch of the connection points, density of the components, Printed Circuit Board (PCB) material and design, and component termination location to name a few. The control method proposed in this paper attempts to find the optimal reflow oven recipe (the temperatures of the oven zones combined with the conveyer speed). This requires “tuning” to achieve a reflow profile (characterization of a fully populated CCA through the oven recipe) that remains within the acceptable window of temperatures and durations for the solder paste and all components. The proposal focuses heavily on Bottom Terminated Components (BTC), especially Ball Grid Array (BGA) components, but does not overlook the solder paste and other component requirements.

Lead-based solder alloy has been used for a long time as solder material in electronic industry. However, its usage in electronic industry has been restricted due to its toxicity to human health and negative impact on the environmental. Lead-free solder alloy was developed to replace the lead-based solder alloy. The properties of this lead-free solder alloy must be the same or much better than the lead-based solder alloy. In this research, the influence of bismuth (Bi) as alloying element on the solidification of tin copper (SnCu) lead-free solder alloy were studied and investigated. The SnCu+xBi where x = 1.5, 3, 4.5 6 wt.% lead-free solder alloy were fabricated by using casting process. To study the wettability, formation of intermetallic compound (IMC) layer, microstructure and hardness, the SnCu+xBi lead-free solder alloy were reflow on Cu substrate by using reflow oven. Overall, addition of Bi as alloying element does influence the characteristics and properties of SnCu lead-free solder alloy in an effort to replace the lead-based solder alloy in electronic industry.

Selective soldering is the process of soldering components to printed circuit boards that could not be treated in a reflow oven in a traditional surface-mount technology process due to thermal shock and damaging. Process of flux appliance as a first step of the selective soldering process sets the baseline for achieving high quality and robustness of the soldered joints. Purpose of this research is to identify the factors that directly influence the effectiveness of the fluxing process in selective soldering machines, using the design of experiment methodology with associated factors and levels used in the experiment. Final findings gives directions for set up of the optimal fluxing parameters that will enable appropriate flux appliance and to gain reduction of soldering quality issues which foundations are from this process.

The joint technology using ultrasonic welding is used to bond plastic material. Currently there are many researches to study the feasibility of using ultrasonic bonding to joint other materials. This paper reviewed the study on using ultrasonic bonding to joint multi metal, surface mount component, and textile material. The process configurations of each material are discussed and the results for each study are also presented. The multi metal materials bonding result shows that these materials bonded well to each other. The ultrasonic bonding strength for SMT components was as good as reflow oven and it was cosmetically accepted. The configuration of textile materials is investigated using vibrating ultrasonic horn and stationary anvil using high mechanical vibration and the result show it can be integrated ultrasonically. With advancement of computer control in ultrasonic welding, this technology can be used for any material in future to achieve world class manufacturing.

Package-on-package (PoP) assemblies may experience warpage during package fabrication and later during surface mount assembly. Excessive warpage may result in loss of coplanarity, open connections, misshaped joints, and reduction in package board-level reliability under environmental stresses of thermal cycling, shock, and vibration. Previous researchers have shown that warpage may be influenced by a number of design and process factors including underfill properties, mold properties, package geometry, package architecture, board configuration, underfill and mold dispense and cure parameters, and package location in the molding panel. A comprehensive inverse model incorporating a full set of design and process parameters and their effect on PoP and PoP assembly warpage is presently beyond the state of the art. In this paper, data have been gathered on multiple PoP assemblies under a variety of assembly parameters. The packages have been speckle coated. The warpage of the PoP assemblies have been measured using a glass-top reflow oven using multiple cameras. Warpage measurements have been taken at various temperatures of the reflow profile between room temperature and the peak reflow temperature. Finite-element models have been created, and the PoP warpage predictions have been correlated with the experimental data. The experimental data set has been augmented with the simulation data to evaluate configurations and parameter variations, which were not available in the experimental data set. Statistical models have been developed to capture the effect of single and multiple parameter variations using principal component regression and ridge regression. The best subset variables obtained from stepwise methods have been used for model development. The developed models have been validated with the experimental data using a single factor design of the experimental study and are found to accurately capture material and geometry effects on part warpage. The results show that the proposed approach has the potential of predicting both single and coupled factor effects on warpage.

This study presents the experimental and numerical analysis of the thermal process for laboratory scale desktop lead-free reflow oven and discusses a 3D CFD model of radiation heating with forced-air convection from circulating stainless steel fan. The experiments were carried out to determine the temperature boundary condition of infrared heating element. In addition, the RPM of the rotating fan was measured using HT50 tachometers. To validate the spatial temperature of the oven, a set of industrial standard thermocouples was employed in various positions. The device was accessed throughout all stages of temperature reflow profile. The profile setting of the oven is in accordance to standard JSTD-020D. The desktop reflow oven was then numerically simulated using the computational model and the advanced user-defined functions (UDFs) were developed to model the thermal profile. The study reveals the temperature distribution of the desktop reflow oven is dependent on the air circulation in the oven at various positions. The temperature contour and air circulation in the oven chamber were demonstrated in the numerical simulation. The experimental and simulation results are useful for further improvement of temperature uniformity within the oven chamber for a convective IR heating reflow oven. The temperature results show a satisfactory agreement with both experiment and simulation.

Purpose – The purpose of this paper is to verify how solder joint properties correlate with soldering profile set-up. These characteristics act against each other. All observed properties may significantly affect the quality and reliability of solder joints. The purpose is also to design recommendations for manufacturers of electronic assemblies. Design/methodology/approach – The samples for experiment were reflowed by using a laboratory reflow oven. A LEXT laser confocal microscope was used for wetting angle and intermetallic compound (IMC) thickness measurement. The ionic contamination was measured by using a contaminometer. Findings – The appropriate choice of soldering profile is very important for the reliability of electronic assemblies. The higher temperatures or longer preheating and soldering times improve the wetting angle. Likewise, there is also the activation of all the fluxes. The result is low contamination with printed circuit boards (PCBs). On the other hand, we must not forget that higher temperatures and longer soldering time also affect the thickness of the IMC. The outer limits recommended by the manufacturer were selected for the soldering profile set-up. Even within these limits, it is possible to achieve an improvement in the wetting angle, an improvement in levels of PCB contamination and an increase in the thickness of the IMC. This paper presents the results achieved for solders Sn42Bi57.6Ag0.4, Sn96.5Ag3Cu0.5 and Sn97Ag3. Originality/value – The gained knowledge on the correlation between IMC thickness, solderability of PCB and PCB contamination caused by different soldering profile set-ups can help to prevent reliability problems because each of the named effects has a significant influence on reliability.

This study applies the reflow optimization process to investigate the phenomenon of spalling in aerospace backward compatibility solder joints when utilized with a Ni substrate [electroless nickel immersion gold, printed circuit board surface finish, and ball grid array (BGA) pads]. The backward compatibility assembly comprised a lead-free tin–silver–copper (96.5Sn3.0Ag0.5Cu/SAC 305 alloy) solder ball assembled with tin–lead paste. The soldering of the lead-free BGA was conducted using two reflow temperature profiles and two conveyor speeds under a nitrogen atmosphere in a full convection reflow oven. The optimized reflow profile has peak temperatures ranging from 237.06 to 237.09°C for 68.94–69.36 s. Scanning electron microscope reveals intermetallic compound formation with maximum thicknesses which are lower than 12 μm as per aerospace requirement. Intermetallic compound spalling of solder ball interface components was not observed. However, spalling between printed circuit board and solder bulk was noted. Nevertheless, at both reflow temperature profiles, the composition and phase distribution of the lead-free BGA ball and tin–lead solder paste were fairly uniform across all joints. This work also presents a finite element-based simulation of backward compatibility assembly in reflow process. A growing number of manufacturers are changing their components to lead-free types without notifying customers. If an aerospace production line is still running a tin–lead-based process, understanding how these lead-free components are processed with tin–lead solder becomes essential. This paper will serve as a reference for manufacturing engineers, particularly those involved in surface mount technology application.

Cooling periods in the reflow soldering process significantly influence heat transfer coefficient and temperature distribution on solder joints, which constituently contribute to soldering defects. The domain of a desktop lead-free reflow oven was built based on the actual dimensions of a sample in GAMBIT 2.3.16. The model was exported to FLUENT 6.3.26 for further parametric study. After grid independency test, simulation results were validated by experimental data according to the American Society of Mechanical Engineers standard for computational fluid dynamics and heat transfer. Next, a simulation model was used to analyze the correlation between temperatures, heat transfer coefficient, and heat flux against reflow cooling durations. Results revealed that a very high radiation heat flux (122.760 W/m2) in a short cooling duration result in unmelted solder powders, which contribute to poor wetting. However, the reduced heat flux of 9.262 W/m2 affects the mechanical properties of solder balls with its continued cooling. Temperature variation and heat transfer coefficient on different points of the substrate are attributed to the non-uniform airflow distribution during the cooling stage. To sum up, the numerical investigation correlates temperature, heat transfer coefficient, and heat flux distribution on different reflow cooling periods to determine their effect on soldering quality.

this paper introduced the important soldering interconnect technology in SMT. In electric product manufacturing process, sometime we must place components in through-hole ways , then we use wave soldering. Wave soldering is used for both through-hole printed circuit assemblies, and surface mount. As technology changing very soon, the through-hole components have been largely replaced by surface mount components, this time ,Reflow soldering is the most common method of attaching surface mount components to a circuit board,but not wave soldering also reflowing, we must focus on wetting , It quantifies the wettability of a solid surface by a liquid .wetting angle is a the important quantity (also called contact angle).it can judge the quality of solder joints.

One step chip attach materials (OSCA) are dispensable polymeric materials for flip chip assembly, which are designed to flux metallic interconnections and subsequently turn into an underfill upon curing. OSCA materials enable a drastic simplification of the assembly process by combining the reflow, flux residue cleaning and capillary underfilling steps used in traditional die attach processing into a single step. A key challenge when designing OSCA materials for conventional mass reflow processing (identified as OSCA-R) is timing the cure kinetics with the fluxing and soldering sequences during reflow processing. OSCA-R materials must also have a process-friendly rheological design that integrates seamlessly with standard dispensing equipment and enables the filler loading levels required for customized thermal conductivities. The consideration of the interactions between the filler particles and the organic portion of OSCA materials is critical for first achieving fluxing and interconnection during reflow and second curing the material to develop target thermo mechanical properties for reliability such as Tg, TC, CTE modulus and adhesion after reflow. This paper presents research focused on understanding the impact of filler loading, size, type and surface chemistry on curing, fluxing and interconnection kinetics during reflow processing measured by thermal and rheological methods. Preliminary results indicate the presence of chemical interactions between the filler and organic formulations, as well as complex physical interactions which need to be considered in the design of OSCA-R materials for a device assembly using conventional mass reflow processing.

No matter what the welding technology, should ensure that meet the basic requirements of welding, welding to ensure good results. High quality welding should have the following 5 basic requirements: 1. appropriate heat; 2. good wetting; 3. appropriate solder joint size and shape; 4. controlled tin flow direction in the welding process; 5. the welding surface does not move to have enough solder joint life, we must ensure that the shape and size of solder joint with welding end structure. The mechanical strength of the solder joint is too small, unable to withstand the stress in use, even after the welding stress is unable to bear. But once in use began to appear fatigue or creep cracking, the fracture speed is rapid. The shape of the solder joints will cause bad homes from the phenomenon of light, life expectancy shortened the solder joint.

Reflow Oven is one of the equipment in an SMT line that performs the soldering phases of the SMD components. These components were previously placed on the PCB that has been coated with solder paste at the corresponding copper pads. The Reflow Oven developed here has heating elements to produce time-varying temperature, with a profile according to the desired specification at each solder-reflow phase. This paper describes the design, implementation, and testing of the hardware, software, and and their integration in the reflow oven machine. The temperature control system uses a PID control algorithm. The values of the PID parameters are determined using Ziegler- Nichols method. Through the GUI, the user can program the temperature profile and will be able to monitor and record the temperature change in the oven in real-time. The reflow oven prototype developed in this work has been tested and is able to be used to assemble a number of functioning SMT boards each of which contains an 8 pin SOIC 555 Time IC.

White light-emitting diodes (LED) are widely applied in many fields for its special advantages compared with other light sources. Chip-scale-package (CSP) is one of the hotspots in the research of microelectronics, and also the main stream and development direction to the future package technology. Within a CSP, the solder layer between LED chip and substrate is usually achieved via reflow processes. The weldability of solder layer with substrate directly determines CSP's reliability and service life. Therefore, optimizing reflow soldering process can improve the performance of solder layer, and improve the reliability of CSPs. The Sn-3.0Ag-0.5Cu (SAC305) has been widely used in high power LED CSPs for its good solderability and favorable shear strength. In this paper, the reflow soldering process for SAC305 is optimized, by considering the reflow profile, the volume of solder paste and the substrate materials, to improve the bonding strength between solder layer and substrate. Then the shear tests and simulation results are used to verify the mechanical performance of CSP solder layer. Finally, an optimized reflow process is proposed for white LED CSP packaging. The results show that the reflow temperature curve should be in an appropriate level, and the performance of the ceramic substrate is more suitable for the SAC305 solder paste than the aluminum substrate.

The development of solutions for high power packaging systems requires the use of a die attach material that has high thermal conductivity and low electrical resistance. However, solder paste, one of which meets this design requirement, is often affected by solder voids that form during the reflow process. By using a 3-factor full factorial design of experiment, this study looks into the effects of reflow profile, nitrogen flow rate, and leadframe type (A and B) on single and cumulative voids produced during the reflow process. Also, the effect of the location of specific nitrogen vents in the machine with respect to the package during reflow processing will be discussed. Analysis of data collected shows that use of higher N2 flow rate, leadframe type A, and reflow profile with higher time above liquidus and soak time reduces both single and cumulative void dppm by more than 95%. This is attributed to lower oxidation and increased flux outgassing during solder reflow.

[EN] This project has carried out the design of a reflow oven for welding surface-mount components (SMD) on printed circuit boards (PCBs). Using knowledges of electronic design, control and programming techniques learned during the grade a recreation of the interior of an industrial reflow oven from a commercial kitchen oven with the relevant modifications has been made. As a result of the inclusion of a control that also contains the PID control, the data output is accessible to the operator at all time, as a result a the obtained system can monitor the thermal process in a simple way for any operator to be able to make use of it., [ES] En este proyecto se ha llevado a cabo el diseño de un horno para soldadura de componentes de montaje superficial (SMD) en placas de circuito impreso (PCB). Mediante el uso de técnicas de diseño electrónico, control y programación aprendidas durante el grado se ha tratado de recrear el interior de un horno de refusión industrial partiendo de un horno comercial de cocina con las modificaciones pertinentes. Como resultado de la inclusión de un mando que contiene también la parte encargada del control PID y la salida de datos accesible para el operario en todo momento, se consigue así un sistema que monitoriza a tiempo real el correcto seguimiento térmico del proceso de una forma clara y sencilla para que cualquier operario sea capaz de hacer uso de él.

This paper encompassed of the evolution and key findings, critical technical challenges, solutions and bonding equipment of solder reflow in flip chip bonding. Upon scrutinizing researches done by others, it can be deduced that peak temperature, time above liquidus, soak temperature, soak time, cooling rate and reflow environment played a vital role in achieving the desired bonding profile. In addition, flux is also needed with the purpose of removing oxides/contaminations on bump surface as well as to promote wetting of solder balls. Electromigration and warpage are the two main challenges faced by solder reflow process which can be overcome by the advancement in under bump metallization (UBM) and substrate technology. The review is ended with a brief description of the current equipment used in solder reflow process.

Purpose – This paper aims to compare and study two-dimensional (2D) and three-dimensional (3D) computational fluid dynamics simulation results of gas flow velocity in a convection reflow oven and show the differences of the different modeling aspects. With the spread of finer surface-mounted devices, it is important to understand convection reflow soldering technology more deeply. Design/methodology/approach – Convection reflow ovens are divided into zones. Every zone contains an upper and a lower nozzle-matrix. The gas flow velocity field is one of the most important parameters of the local heat transfer in the oven. It is not possible to examine the gas flow field with classical experimental methods due to the extreme circumstances in the reflow oven. Therefore, numerical simulations are necessary. Findings – The heat transfer changes highly along the moving direction of the assembly, and it is nearly homogeneous along the traverse direction of the zones. The gas flow velocity values of the 2D model are too high due to the geometrical distortions of the 2D model. On the other hand, the calculated flow field of the 2D model is more accurate than in the 3D model due to the finer mesh. Research limitations/implications – Investigating the effects of tall components on a printed wiring board inside the gas flow field and further analysis of the mesh size effect on the models. Practical implications – The presented results can be useful during the design of a simulation study in a reflow oven (or in similar processes). Originality/value – The presented results provide a completely novel approach from the aspect of 2D and 3D simulations of a convection reflow oven. The results also reveal the heat transfer differences.

The reflow soldering process under infrared hot air environment was simulated based on a typical BGA SMA and a twelve-zone reflow oven. Then the optimal soldering process parameters were obtained based on 6σ analysis method and related software. The results could be used to direct the lead-free soldering process parameters setting, and the soldering quality was ensured effectively.

In this paper, we present a highly effective vacuum seal method, which is based on anodic bonding assisted by the reflow of lowmelting temperature metal. To form sacrificial gap for evacuating the packaged cavity before hermetically sealing, the reflow process of Au/Sn/Cr posts due to low-melting temperature Sn metal was introduced. Using this technique to form the evacuation gap, the micro-precise alignment between packaging wafers was obtained. The package method enabled to eliminate contaminant caused by package process. The diaphragm structure sensing pressure was used to investigate the proposed package method. The vacuum level in the packaged cavity was obtained lower than 5 Pa. In comparison to the conventional package method without using the reflow process to form the evacuation gap, the vacuum level has been improved by a factor of 8. The yield and uniformity of the package method were also confirmed to be higher than the conventional package method without using the reflow process to form the evacuation gap. This vacuum package method can be implemented to remove air damping for optimal performance of mechanical oscillators such as accelerometers, gyroscopes, energy harvesters, and micro-mirrors.

In this paper, numerical study of the gas flow velocity space is presented in a convection type reflow oven. Convection reflow ovens usually apply the nozzle-matrix heater system which generates numerous gas streams perpendicularly to surface of the soldered assembly. The ovens are divided into zones; every zone contains an upper and a lower nozzle-matrix. The temperature can be independently controlled in each zone; however the velocity of the influent streams is usually fixed. The gas flow velocity space is one of the most important parameter of the local heat transfer coefficient in the oven. The gas flow space cannot be examined by classical experimental methods due to the extreme circumstances in the reflow oven. Therefore the effect of the soldered assembly, the different component sizes, the position of the conveyor belt and the vent hood between the zones on the gas flow velocity space was studied by CFD simulations. These results can be useful during the overview of the actual assembly design and manufacturing rules.

The paper presents the quantification of void formation in lead-free solder joints underneath bottom terminated components (BTCs) through X-ray inspection. Experiments were designed to investigate how void formation is affected by using vacuum in reflow soldering on the example of light emitted diode (LED) packages on metal core printed circuit boards (PCBs). Convection and vapour phase reflow soldering were used for LED assembly. X-ray inspection system analyzed the statistical distribution, mean value, standard deviation and process capability value Cpk of thermal pads coverage for various technological versions of LEDs.

Package-on-package (PoP) is one of the major manufacturing strategies for achieving an electronic component miniaturization. Achieving a desired process yield is critical to maintaining competitiveness. This paper develops a scientific approach to assess the PoP assembly yield in both the x- y in-plane and the z-direction using a Monte Carlo simulation. Influences of variations of materials such as components and printed circuit boards (PCBs) are investigated. Equipment accuracy and different process strategies are also under consideration. The scenarios under which defects occur are defined through the geometric phenomena, process incidence, and theoretical inferences. Defects such as shorts and soldering open may occur after reflow soldering if there is an excessive amount of offset between the centers of the solder ball and the bonding pad during the component placement stage. The amount of component/PCB warpage during the reflow heating and coplanarity of the solder balls beneath the substrate will also impact the package stacking yield. The simulation-based design for experiment is employed to investigate the effects of soldering materials, stencil thickness, reflow temperature profile, and component ball height variation on the assembly yield. The optimal materials and process combinations are then identified.

This paper reports the factors that affect the bump height in electroless nickel immersion gold (ENIG) and their interrelation between each other. Bump height is a critical issue that needs to be investigated because a certain quality and requirements of bump height needs to be achieved prior to reflow oven soldering process. A total of four controllable process variables, with 16 sets of experiments were studied using a systematically designed design of experiment (DOE). The result suggests that the electroless nickel bath time has the most significant effect on the formation on bump height and consequently provide larger area for conductivity.

Reflow soldering process parameters have distinct effect on the lead-free reflow profile and its key indicators. To determine the relationship between reflow soldering process parameters and lead-free reflow profile is significant for obtaining the correct reflow profile. The result of orthogonal experimental shows that the most influential factors of the change rate of heat-up RS are conveyor speed S, temperature set value of the heating zone 1 T1 and the temperature set value of heating zone 2 T2 in sequence; the most influential factors of the soaking time TS are conveyor speed S, the temperature set value of heating zone 4 T4 and the temperature set value of heating zone 2 T2 in sequence; the most influential factors of the reflow peak temperature PT are conveyor speed S, the temperature set value of heating zone 7 T7 and the temperature set value of heating zone 6 T6 in sequence; the most influential factors of the reflow time TAL are conveyor speed S and the temperature set value of heating zone 6 T6 in sequence.

The objective of the present study is to develop a Fluid/Structure Interaction model of a board-level Ball Grid Array (BGA) assembly for an infrared-convection reflow oven. The infrared-convection reflow oven is modeled in Computational Fluid Dynamic (CFD) software while the structural heating BGA package simulation is done using Finite Element Method (FEM) software. Both software applications are coupled bidirectional using the Multi-physics Code Coupling Interface (MpCCI). The simulation thermal profile is compared with the experiment thermal profile, and they were found to be in good conformity. The simulated flow fields show that the convection mode in an infrared-convection reflow oven played minor effect on heat transfer to the printed circuit board (PCB). The dominant heat transfer mode in an infrared-convection reflow oven is the radiation mode from a quartz heating tube. From the simulation results, the PCB near the edges or corners tended to heat up first at preheating, soaking and reflow stages. The PCB and component experience larges temperature difference in preheating stage. This situation runs the risk of an excessive board warpage. In addition, the maximum von-Mises stress is trapped in the interfaces between solder joint and die, which intend to form the nucleation of initial solder joint crack. This guideline is very useful for the accurate control of temperature and thermal stress distributions within components and PCB, which is one of major requirements to achieve high reliability of electronic assemblies.

The aim of this paper is to investigate temperature and thermal stress responses at various joint arrangements during the cooling stage of the reflow process using an effective numerical approach. In this approach, numerical techniques for computational fluid modeling of the internal flow in the reflow oven were coupled with the structural cooling modeling at the board and package levels using a multi-physics code coupling interface. A thermal profiling experiment was conducted using the forced convection reflow oven to validate the simulation model. The numerical results were found to be in agreement with the experimental results. Results showed that the full-grid ball grid array (BGA) package has greatest temperature deviations, indicating different time responses between the start of the solidification process at different locations of the soldering process. Moreover, the solder joints experienced phase change from liquid to solid during the cooling stage of the reflow process. The large time interval for mushy zone of the full-grid BGA package indicated that the latent heat in a solder joint was hardly released to the environment. Consequently, this breaks the balance of the wetting force and increases the chances of the full-grid BGA package to skew. Generation of thermal stress at the interfaces of different materials occurred due to the mismatch of a variant coefficient of thermal expansion. Analysis and visualization of simulation results also showed that the maximum von-Mises stress of critically affected joints is influenced by solder joint arrangement patterns and not by the number of solder joints. The recommendation was also made to place dummy joints at the center of a package if routing and solder cracking problems were critical for peripheral array BGA package. The maximum von-Mises stress was reduced by 25.78% through improvement of solder arrangements. On the whole, the newly developed approach greatly helps reduce soldering defects and enhances solutions to lead-free reliability issues.

Reflow soldering is one of the most widespread soldering technologies used in the electronics industry. It is a method of attaching surface components to a circuit board with solder paste. The goal of the reflow process is to melt the solder and heat the adjoining surfaces, without overheating and damaging the electrical components. In the present study, computational fluid dynamics (CFD) was used to investigate the convection flow field during the cooling reflow process stage. The convection heat-transfer coefficient and temperature distribution within the board level were also studied. The analysis comprises three main objectives: (1) the simulation of the cooling process of a PCB in the final section of the reflow oven; (2) the calculation of the heat transfer from the PCB to the air as the PCB moves throughout the woven; and (3) use a “dummy” PCB with two generic components with different dimensions and analyze the heat dissipation. The geometry definition, the mesh generation, as well as the numerical simulations were carried out using the Workbench™ platform from ANSYS® 15. It was programmed an UDF to represent the relative motion between the PCB and the cooling air flow. Results shown that, during the cooling process, there is a gradient over the PCB board. It is also observed that there is a small differentiation in the temperatures’ profile along the board length probably because of the formation of recirculation areas inside the oven. Thus, nozzle spacing has a great impact in the formation of those recirculation areas, and consequently in heat dissipation.

In this study, it is shown that temporary tacking (without flux and temporary tack materials) is feasible to temporary tack Cu/SnAg or SnAg sealing ring onto Cu sealing ring at the bottom wafer. The temporary tacked samples were reflowed in a formic acid environment and this allowed the removal of the native oxide of solder. The removal of oxide provides a good solder joints formation during reflow [4]. Vacuum reflow with formic acid and load of 20g per unit showed good sealing results. Helium leak test for chip on silicon substrate was carried out. The results indicated the leak rate at the level of ≤ 5×10−8 atm cc/s Helium can be achieved. Chip on wafer (CoW) bonding with hermetic sealing was demonstrated on 8″ wafer with cavity.

Some limitations are observed on complex high density boards with convection ovens processing lead free alloys. Vapour phase soldering process offers excellent heat transfer capabilities and high wetting performance, and it has become a real option to be considered, including medium to high volume production, in high reliability applications. Traditionally, pastes used in such process were designed to be cleaned after reflow as they were mainly dedicated to aeronautics or military. Today, other electronics assembly markets (industry, automotive) are looking for No Clean pastes able to stand both convection and vapour phase reflow. Peak temperatures are much lower in a vapour phase oven: flux activators may not be fully consumed because oxidation is minimized. Flux residues remaining on the boards may cause corrosion in harsh environment, even when using no-clean solder pastes. Firstly, the cleanability of several no-clean solder pastes will be compared after vapour phase and after convection soldering. Different defluxing processes are considered. Secondly, the chemical reliability of the same group of No Clean pastes will be assessed after vapour phase reflow in comparison to convection reflow. Surface insulation resistance (SIR) and electrochemical migration (ECM) will be used as a first tool. Then Bono corrosion test will be used. The behaviour of several No Clean solder pastes, in terms of cleanability and chemical reliability will be described according to the reflow process applied.

The electronics industry is switching the majority of their mobile roadmaps to Ball Grid Array (BGA) packages in order to enable thinner form factor devices. Original Equipment Manufacturers (OEMs) have to solder down the packages to their production boards since there is no form-factor production BGA socket available in the industry. This raises several challenges for the OEM supply chain and increases overall product costs. In addition to the overall added height of the socket, one technical challenge that faces the OEM BGA socket is the long-term reliability of the interface between the socket's gold-plated contacts and the package's SAC solder balls. This non-noble metal interface creates the risk of intermetallic formation and growth over the product life cycle, which will cause a bond formation and affect the removability of the BGA; it could also increase the overall resistance of the next socketing cycle due to the intermetallic residue left on the pins. This paper presents an attempt to overcome the interface challenge by re-balling the BGA with gold-plated copper spheres. Several design and SMT process parameters affect the overall re-balling quality. In particular, solder wicking is a major challenge. This paper presents an attempt to optimize the design and SMT process parameters for better results. Pad size, pad define, stencil thickness, stencil aperture size, copper sphere size, and reflow oven vs. SRT are some of the parameters that were studied.

The paper describes the results of investigations concerning the behaviour and joint quality of various die attachment materials on DBC (Direct Bonded Copper) Al 2 O 3 based substrates. A comparative study of influence of various material on joint quality was realized. Experimental samples were reflowed in a vacuum reflow oven, and in a vapour phase soldering (VPS) chamber. For the first time were applied new developed solder materials (Sn 96.5 Ag 3.5 and Sn 95.9 Cu 3 In 1 Ag 0.1 alloys) in the form of thin ribbons. The new metals and alloys were prepared by the rapid solidification technique — melt spinning at a cooling rate of 106 °C/s. First measurements show that the new materials meet high requirements on joints properties: better thermal conductivity and mechanical strengths, less voids and better thermo-mechanical reliability. The thin ribbons based on the melt spinning (rapidly cooled) materials are a promising candidate for use in the die attachment in power electronics.

Low-temperature soldering of 6061Al by an aluminum solder paste consisting of a purpose-designed flux and Sn-0.3Ag-0.7Cu (SAC0307) solder alloy powder with different reflow process parameters (such as the heating rate, peak soldering temperature and joint thickness) and the reliability of the soldered joints were investigated in this study. With increasing the heating rate, the spreading performance of the paste on 6061Al increases, and the tensile strength and shear strength of 6061Al/SAC0307/6061Al solder joints increase observably, which is due to the fact that the activity of the aluminum solder paste increases with the increase of heating rate in reflow process. However, the effects of peak soldering temperature on the solderability of the aluminum solder paste and the reliability of the soldered joints may be negligible. There is no intermetallic compound or transition layer formed at the interface. In addition, the shear strength of the joints increases with the increase of joint thickness because of the less voids formed in the solder matrix.

This paper deal with the description of possibilities in designing of infrared heaters for reflow soldering. Main work was divided into two parts, simulation and realization. Simulation helps find the best solution of IR heater arrangement. The research was focused on the homogeneity of transferred heat to soldered component. In realization part, there was manufactured a prototype of IR heater in the best solution.