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Increases in component packing density and the consequent decrease in feature size in electronics products continue to place ever more emphasis on process design to manage or predict the outcome of the inherent process/materials interactions. The most significant pressure is for improved first‐off process yields because of high cost and technical difficulty of rework processes and concerns about the life of reworked products. The current dominant process for the production of surface mount assemblies is the reflow soldering of stencil printed solder paste. This paper presents the results of work that begins to describe the sub‐processes of solder paste reflow. It is essential to understand and optimise these complex physical processes when aiming for the six‐sigma level quality demands of electronics manufacture.

Although wave soldering is a long established technique, the touch‐up percentage is still unacceptably high. This leads to high touch‐up costs and too low product quality. One cause lies in the fact that the complexity of the boards is increasing all the time (greater component density, greater diversity, more leads and smaller pitches). The main reason, however, lies in the lack of a fundamental process technology background. This becomes even more serious now that soldering processes are becoming more critical. The touch‐up percentage can and must be lowered through accurate process adjustment and control. A further improvement in process adjustment and control will give a considerable improvement in soldering quality in the short term. In this way, the actions are successful, although benefits can be achieved only if the improvements are consolidated. Further improvements can be achieved through systematic application of design rules.

Implementing surface mount technology (SMT) into military systems has not progressed as rapidly as expected. One of the major reasons is the lack of availability of MIL Spec. surface mountable components. Therefore, if one is to realise the benefits of SMT, manufacturing processes must be developed that allow inserted components to be mounted on the same printed wiring board (PWB) with surface mount components (SMCs). Honeywell's Ordnance Division has developed manufacturing processes which allow SMCs to be mounted on both sides of the PWB and inserted components to be mounted on one side of the same PWB. The surface mount solder reflow and wave soldering are performed in a single‐step solder system. This simplifies and reduces the number of manufacturing process steps for this type of surface mount assembly (SMA). This paper describes three major types of SMAs and their complexity levels. Definitions of the SMA types and complexity levels are necessary for selecting production equipment and developing SMA processes. Assembly process limitations are directly related to the SMA type and complexity level. Layout guidelines and processes from solder deposition to cleaning are discussed. Full scale engineering development (FSED) hardware has been fabricated using the single‐step solder process for SMAs with both SMCs and inserted components on the same PWB. The single‐step solder process offers an excellent solution to fabricating electronic assemblies where SMCs and inserted components are mounted on the same PWB. Plans to expand and enhance the first generation SMA fabrication processes to accommodate higher complexity levels are discussed.

Today's electronic assembly manufacturing operations can be complex combinations of process steps such as IR reflow, wave soldering, special soldering of connectors or sensitive components, cleaning, rework, etc. Such multiple exposures to elevated temperatures and/or oxidising environments (e.g., aqueous cleaning) can have a negative effect on the solderability of printed wiring board (PWB) surfaces. This in turn may limit the effectiveness of subsequent soldering operations, such as wave soldering following an IR reflow step. The purpose of this study is to assess the impact of individual assembly process steps on the solderability of PWB surfaces. The PWB surfaces are initially treated with protective coatings of benzotriazole (BTA). The process steps investigated include: IR reflow in air and in nitrogen; vapour phase reflow; aqueous cleaning; adhesive cure; and wave soldering as a function of solder temperature and flux type. Meniscograph wettability testing is used to measure relative solderability changes, and Auger electron spectroscopy (AES) is used to monitor surface chemical changes, particularly oxide formation. The overall result is a body of fundamental information providing insight into optimisations of process flows, equipment operating specifications, process temperatures and selection of flux types.

A new product design required the addition of a second layer of electronics to control a base module. This product was designed with significant overhangs of heavy leads and components which presented a significant challenge to many different solder assembly processes. Only the heated gas jet process was able to solder the product successfully without damaging the printed wiring boards.

To answer the challenge, a new machine was developed, combining dispensing of solder paste with hot gas jet reflow technology. This provided a combination of capabilities resulting in a flexible process which was significantly superior to alternative technologies.

Other soldering processes such as laser, focused xenon lamp, robotic soldering iron, and focused IR soldering technologies were evaluated. Each of these technologies causes some damage or defect to the assembly due to the heat sinking aspect of the circuit assembled. These alternative processes would create damage or defects to the assemblies by burning the laminate, delaminating the pads on the printed wiring board, or not soldering the pads.

Proof of concept tests before machine designs were initiated demonstrated the potential and capabilities of this technology for automated assembly soldering. Testing indicated that the heated gas jet processing would provide a means of soldering the assemblies at a controllable rate without damaging the circuit boards.

While evaluating the machine ion its design phase, a designed experiment was initiated to help understand the relationships between head temperature settings versus gas flow rates, the measurable output was time to reflow.

The process meets all expectations in terms of solder fillet appearance, volume, and overall visual quality while maintaining process cycle time requirements.

The purpose of this paper was to develop a physics-based mathematical model to estimate the amount of substrate metal lost during the wet soldering process.

A mathematically rigorous model depicting the actual physics of the substrate/solder interaction and dissolution has been proposed to simulate the dissolution of the substrate metal in the liquid lead-free solder. The basic mass diffusion equation with the implementation of interface reaction kinetics was solved numerically using the finite volume approach. The moving interface was tracked by utilizing the coordinate transformation technique.

It was observed that the process of metal dissolution in the liquid solder was governed by two important parameters, viz., interface kinetics and long-range diffusion in the liquid solder. Non-equilibrium behavior was observed in the early stage of the process. The early stage of the dissolution process was seen as governed by interface kinetics, while diffusion became the rate-controlling mechanism at the later phase of soldering.

Substrate dissolution can be accurately estimated for a particular substrate–solder combination and for the given process conditions. This early estimation will help in ensuring the reliability and health of the solder joint.

A model based on actual physics is proposed, and interface reaction kinetics has been introduced to capture the actual behavior of the process. The model will serve as the basis for two- and three-dimensional analysis, including the formation of an intermetallic compound in the solder joint.

Power electronics are usually soldered to Al₂‐O₃ direct‐bond‐copper (DBC) substrates to increase thermal diffusivity, while at the same time increasing electrical isolation. However, soldering gives rise to inherent residual stresses and out‐of‐plane deformation. The purpose of this paper is to look at the effect of soldering processes of Al₂‐O₃ DBC substrates to copper plates and power electronics, on their thermal fatigue life and warpage.

A numerical thermo‐mechanical finite element model, using the Chaboche material model, was developed to identify the thermal plastic strains evolved during soldering of DBC substrates to copper plates and power electronics. The plastic strains in conjunction with established extremely low cycle fatigue life prediction model for ductile material were used to predict the number of soldering cycles to failure. The predicted out‐of‐plane deformation and number of soldering cycles to failures was compared to realistic tests.

Soldering processes drastically reduce the thermal fatigue life of DBC substrates, giving rise to thermal cracking and premature failure. In this study the soldering process considered gave rise to out‐of‐plane deformations, consequently reducing heat dispersion in soldered DBC substrate assemblies. Furthermore, soldering gave rise to interface cracking and failed after three soldering cycles. Numerical finite element models were developed and are in good agreement with the experimental tests results.

The influence of soldering processes of DBC substrates to copper plates and electronics on the thermal fatigue life should be taken into consideration when establishing the design life of DBC substrates. Finite element models can be utilised to optimize soldering processes and optimize the design of DBC substrates.

The effect of soldering processes on DBC substrates was studied. A numerical finite element model used for the prediction of design life cycle and out‐of‐plane deformation is proposed.

The traditional surface finish for bare boards, eutectic tin‐lead solder from the HASL process, is well characterized, but very little is known about the implementation of lead free solder in that application. This paper will present the results of a study that defined process parameters for both horizontal and vertical machines.

A test vehicle containing high aspect ratio PTH technology and fine pitch surface mount pads was used for the testing. Solder samples were taken while copper clad laminates were run through the machine. Test panels were run after each 100 laminates and were assessed for solder coverage, appearance, thickness and distribution. Board cleanliness was measured by SIR and ionic contamination.

Operating parameters for the respective machines were established. Fluxes and oils were found to meet the requirements. Bright solder coatings produced on test panels contained no exposed copper and were found to meet industry standards. SIR results met the requirements of SM‐840C.

Future research to analyze and replenish the lead free solder pot with tin and nickel is needed to assist board shops with the production use of the process over a longer period of time. The work of this paper covered a few days of simulated production, depending on the daily throughput.

Work has been done and reported to demonstrate that the Lead Free HASL is a viable process ready for commercial implementation.

The work of this paper will allow a circuit board fabricator to have a starting point to implement the lead free HASL process. Copper and nickel tracking data are helpful to set up a solder dilution schedule to maintain their concentrations within operating limits.

PCB manufacturers are switching from the use of RMA fluxes in their soldering and rework processes to low residue type (i.e., ‘no‐clean’) fluxes. Unfortunately, successful changeover is not simply a matter of substituting a no‐clean into an existing RMA process. Soldering process parameters must change, necessitating an understanding of the interplay between flux chemistry and heat delivery. Higher temperatures can result in an effective decrease in the concentration of the active fluxing agents. Also, data show a decrease in the inherent wetting force of a no‐clean flux with increasing temperature. These two factors reduce fluxing action below the rate of oxidation occurring at the solder connection and the soldering iron tip. These can lead to incomplete surface cleaning and inefficient heat transfer, resulting in poorly soldered connections. Lower solder joint defect rates are obtained with no‐clean solders and fluxes when soldering temperatures are reduced to a minimum.

The purpose of the paper is to focus on the research into components with specific thermal properties and their influences on the reflow soldering process.

After a brief introduction, the paper gives an overview of the necessity of thermal management on printed circuit boards (PCBs) and the possible effects on the manufacturing of electronic devices. In the next sections, different test boards are presented for investigations into different thermal effects during soldering. The last section deals with the influences of molded interconnected devices (MIDs) on the reflow soldering process.

The investigations show that components from the thermal management influence the reflow soldering process more or less. The highest impacts on the soldering process are from components with a thermal connection to the electrical component and its solder joint. All results from the investigations have in common that the thermal influence can only be compensated by increasing the temperature during soldering. However, this significantly increases the risk of overheating the electrical components or the PCB itself.

This paper shows only the influence of some of the effects caused by thermal management on the reflow soldering process. Furthermore, vapour phase soldering is not considered, but actual investigations are carried out on vapour phase soldering ovens as well.

Thermal management becomes more and more important with the increasing functionality of electrical components and electronic devices. This topic has been the subject of a large number of articles. However, this paper deals with influences that thermal management has on the soldering process during the manufacturing of the electronic device.