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Laser soldering has attracted attention as an alternative soldering process for microsoldering due to its localized and noncontact heating, a rapid rise and fall in temperature, fluxless and easy automation compared to reflow soldering.

In this study, the metallurgical and mechanical properties of the Sn3.0Ag0.5Cu/Ni-P joints after laser and reflow soldering and isothermal aging were compared and analyzed.

In the as-soldered Sn3.0Ag0.5Cu/Ni-P joints, a small granular and loose (Cu,Ni)6Sn5 intermetallic compound (IMC) structure was formed by laser soldering regardless of the laser energy, and a long and needlelike (Cu,Ni)6Sn5 IMC structure was generated by reflow soldering. During aging at 150°C, the growth rate of the IMC layer was faster by laser soldering than by reflow soldering. The shear strength of as-soldered joints for reflow soldering was similar to that of laser soldering with 7.5 mJ, which sharply decreased from 0 to 100 h for both cases and then was maintained at a similar level with increasing aging time.

Laser soldering with certain energy is effective for reducing the thickness of IMCs, and ensuring the mechanical property of the joints was similar to reflow soldering.

The purpose of the present study was to review the thermo-mechanical challenges of reflowed lead-free solder joints in surface mount components (SMCs). The topics of the review include challenges in modelling of the reflow soldering process, optimization and the future challenges in the reflow soldering process. Besides, the numerical approach of lead-free solder reliability is also discussed.

Lead-free reflow soldering is one of the most significant processes in the development of surface mount technology, especially toward the miniaturization of the advanced SMCs package. The challenges lead to more complex thermal responses when the PCB assembly passes through the reflow oven. The virtual modelling tools facilitate the modelling and simulation of the lead-free reflow process, which provide more data and clear visualization on the particular process.

With the growing trend of computer power and software capability, the multidisciplinary simulation, such as the temperature and thermal stress of lead-free SMCs, under the influenced of a specific process atmosphere can be provided. A simulation modelling technique for the thermal response and flow field prediction of a reflow process is cost-effective and has greatly helped the engineer to eliminate guesswork. Besides, simulated-based optimization methods of the reflow process have gained popularity because of them being economical and have reduced time-consumption, and these provide more information compared to the experimental hardware. The advantages and disadvantages of the simulation modelling in the reflow soldering process are also briefly discussed.

This literature review provides the engineers and researchers with a profound understanding of the thermo-mechanical challenges of reflowed lead-free solder joints in SMCs and the challenges of simulation modelling in the reflow process.

The unique challenges in solder joint reliability, and direction of future research in reflow process were identified to clarify the solutions to solve lead-free reliability issues in the electronics manufacturing industry.

For reflow soldering in today's changing component and soldering technology, requirements with respect to profiling seem to be difficult to determine and even harder to meet. State‐of‐the‐art reflow trackers can be of help here, but, without some knowledge of the fundamentals in profiling, it will be easy to misunderstand measurements. The use of nitrogen as a protective gas for reflow soldering can be advantageous for fine pitch technology, bare copper boards and low residue solder pastes. However, because reflow solder defects are related to more than just the use of nitrogen, one may find different benefits for the use of nitrogen, depending on how the investigations are carried out. Wetting under nitrogen is certainly better and more reproducible, while the near absence of oxygen is beneficial to oxidation‐related problems. For high numbers of solder joints per board, it is not easy to achieve an acceptable first pass yield. Only with low, controlled defect levels found within a robust reproducible process is it possible to achieve this. Using forced convection together with nitrogen for reflow soldering is becoming the preferred method.

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 increasing complexity of microelectronic devices and the advent of surface mount technology has led to interest in alternatives to mass reflow soldering techniques. One method with advantages for rapid automation and minimal heat input, is laser soldering. Various laser methods are available for application to reflow soldering, the prime options being continuous wave CO2, continuous wave Nd/YAG and pulsed Nd/YAG. This paper presents the results of work to compare and contrast the three techniques. The paper concentrates on the soldering of leadframes and SMD (gull wing and J‐lead) to plated Al2O3 substrates, but also mentions soldering to FR4 PCBs.

The aim of this paper is to evaluate using statistical methods how two soldering techniques – the convection reflow and vapour phase reflow with vacuum – influence reduction of voids in lead-free solder joints under Light Emitted Diodes (LEDs) and Ball Grid Arrays (BGAs).

Distribution of voids in solder joints under thermal and electrical pads of LEDs and in solder balls of BGAs assembled with convection reflow and vapour phase reflow with vacuum has been investigated in terms of coverage or void contents, void diameters and number of voids. For each soldering technology, 80 LEDs and 32 solder balls in BGAs were examined. Soldering processes were carried out in the industrial or semi-industrial environment. The OM340 solder paste of Innolot type was used for LED soldering. Voidings in solder joints were inspected with a 2D X-ray transmission system. OriginLab was used for statistical analysis.

Investigations supported by statistical analysis showed that the vapour phase reflow with vacuum decreases significantly void contents and number and diameters of voids in solder joints under LED and BGA packages when compared to convection reflow.

Voiding distribution data were collected on the basis of 2D X-ray images for test samples manufactured during the mass production processes. Statistical analysis enabled to appraise soldering technologies used in these processes in respect of void formation.

This paper will review the challenges brought by lead‐free soldering and some preliminary experimental evaluation results will be discussed. The initial results show that the lead‐free soldering process with 260°C reflow peak temperature does not directly cause failures for bismaleimide‐triazine (BT)‐based fine pitch ball grid array (FPBGA) packages. However, the strict lead‐free soldering condition could degrade the integrity of weak interface joints and potentially damage the package in subsequent unbiased highly accelerated stress test (unbiased HAST) evaluation. The impacts of lead‐free soldering with high reflow temperature on concurrent available electronics components could be more severe than previously believed. In the future, new materials and design concepts should be applied to enhance the package reliability under strict lead‐free soldering conditions.

This paper aims to offer a convenient method to develop an oven recipe for a specific soldering profile in a reflow process. The method is devised to quickly achieve proper profile shape and heating factor Q_η, a measure of success for high reliability of the solder joints reflowed.

An in‐depth analysis of the heating mechanism and some experiments of the reflow soldering process are performed to research on how to realize a specific shape reflow profile were conducted.

Heating mechanism analysis and experiments demonstrate that the combinatorial parameters based method is feasible to do thermal profiling.

The mapping function among a particular configured PCBA, an oven used, a target reflow profile and an optimal range of the heating factor should be further established for fast and reliable production of reflow soldering.

Provides a methodology for designing an oven recipe for reflow soldering production.

An oven recipe can be quickly attained with the approach established in this paper, facilitating the formation of solder joints with high reliability during the reflow soldering process.

This paper presents the requirements for infra‐red soldering machines for reflow soldering of printed boards with components for surface mounting. Guidelines for controlling and adjusting the infra‐red reflow soldering process, as well as a computer model to help the user of infra‐red reflow systems to adjust an infra‐red oven, are provided. In specifying the various process conditions, the authors have considered that a careful adjustment of the process parameters will improve the soldering quality.

Several effects of the atmosphere in the soldering oven on both the soldering process itself and the soldering results are discussed. Experiments have been undertaken to compare the results of soldering in air and in nitrogen containing 10,100 and 1000 ppm oxygen, in which, e.g., discolouration, wettability, solderability after reflow, solder bridging and solder‐ball formation were investigated. Unmounted FR‐4 testboards with both an RMA solder paste of known high quality and a low‐residue paste were used. Mounted test boards were used to analyse the self‐alignment of components and to compare the levels of soldering defects obtained in air and in nitrogen. The test results show that a nitrogen atmosphere containing 1000 ppm of oxygen or less is sufficiently pure to realise improved soldering conditions for most types of components. For the low‐residue paste tested, 1000 ppm is too high, but 100 ppm is sufficiently low. All effects on the soldering process will depend on the amount of oxygen in the gas. To produce an oven atmosphere of nitrogen with a very low amount of O2 (e.g., <100 ppm) is rather expensive, if this oven is to work under production conditions. Will the extra cost of investment and gas consumption be worthwhile in view of a better production yield and higher product quality? The authors explain why they do not believe this to be the case.