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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.

The success of vapour phase soldering for electronic assemblies has led to the availability of several heat transfer fluids for the purpose. This paper aims to demonstrate the significance of the differing properties of fluids, illustrated by measurements on the three most commonly used in the UK. These three, as well as any future fluids, can be judged in terms of (i) vapour temperature and its influence on soldering yields and materials properties; (ii) stability of soldering temperature with time; (iii) heat transfer efficiency; (iv) power requirements and thermal control; (v) rosin solubility and flux wash‐off; (vi) toxicity, especially under thermal stress; (vii) corrosivity and its dependence on process control; and (viii) consumption of fluid.

This paper aims to investigate the self-alignment of 0603 size (1.5 × 0.75 mm) chip resistors, which were soldered by infrared or vapour phase soldering. The results were used for establishing an artificial neural network for predicting the component movement during the soldering.

The components were soldered onto an FR4 testboard, which was designed to facilitate the measuring of the position of the components both prior to and after the soldering. A semi-automatic placement machine misplaced the components intentionally, and the self-alignment ability was determined for soldering techniques of both infrared and vapour phase soldering. An artificial neural network-based prediction method was established, which is able to predict the position of chip resistors after soldering as a function of component misplacement prior to soldering.

The results showed that the component can self-align from farer distances by using vapour phase method, even from relative misplacement of 50 per cent parallel to the shorter side of the component. Components can self-align from a relative misplacement only of 30 per cent by using infrared soldering method. The established artificial neural network can predict the component self-alignment with an approximately 10-20 per cent mean absolute error.

It was proven that the vapour phase soldering method is more stable from the component’s self-alignment point of view. Furthermore, machine learning-based predictors can be applied in the field of reflow soldering technology, and artificial neural networks can predict the component self-alignment with an appropriately low error.

This paper will outline a viable, in use, production process that focuses on the utilisation of vapour phase soldering. The process will address the soldering of surface mounted devices, the repeatability of solder joint quality, and the resultant environmental characteristics of assemblies produced using the mentioned techniques. The paper will also address the field history obtained by SMD hardware produced at the author's company, to illustrate the environments into which vapour phase soldered joints can be successfully implemented.

This paper aims to present a review of the recent developments in vapour phase soldering (VPS) technology. This study focuses on the following topics: recent developments of the technology, i.e. soft and vacuum VPS; measurement and characterization methods of vapour space, i.e. temperature and pressure; numerical simulation of the VPS soldering process, i.e. condensate layer and solder joint formation; and quality and reliability studies of the solder joints prepared by VPS, i.e. void content and microstructure of the solder joints.

This study was written according to the results of a wide literature review about the substantial previous works in the past decade and according to the authors’ own results.

Up to now, a part of the electronics industry believes that the reflow soldering with VPS method is a significant alternative of convection and infrared technologies. The summarized results of the field in this study support this idea.

This literature review provides engineers and researchers with understanding of the limitations and application possibilities of the VPS technology and the current challenges in soldering technology.

This paper summarizes the most important advantages and disadvantages of VPS technology compared to the other reflow soldering methods, as well as points out the necessary further developments and possible research directions.

The vacuum vapour phase soldering method was investigated by numerical simulations. The purpose of this study was to examine the temperature changes of the solder joints during the vapour suctioning process. A low pressure is used to enhance the outgassing of the trapped gas within the solder joints, which otherwise could form voids. However, the system loses heat near the suction pipe during the suctioning process, and it can result in preliminary solidification of the solder joints before the gas could escape.

A three-dimensional numerical flow model based on the Reynolds averaged Navier–Stokes equations with the standard k-e turbulence method was developed. The effect of the vapour suctioning on the convective heat transfer mechanism was described by the model. Temperature change of the solder joints was studied at the mostly used substrate and component combinations, as well as at different system settings.

In the function of the substrate thickness and the component size, the solder joints can lose large amount of heat during the void reduction process, which leads to preliminary solidification before the entrapped gas voids could be removed.

The results provide setting information of vacuum vapour phase technology for appropriate and optimal applications.

The relationship between low pressure generation and convective heat transfer mechanism during vacuum vapour phase soldering has not been studied yet. The possible negative effects of the vapour suctioning process on the solder joint temperature are unknown.

The purpose of this paper is to evaluate selected methods of reduction voidings in lead-free solder joints underneath thermal pads of light-emitting diodes (LEDs), using X-ray inspection and Six Sigma methodology.

On the basis of cause and effect diagram for solder voiding, the potential causes of voids and influence of process variables on void formation were found. Three process variables were chosen: the type of reflow soldering, vacuum incorporation and the type of solder paste. Samples of LEDs were mounted with convection and vapour phase reflow soldering. Vacuum was incorporated into vapour phase soldering. Two types of solder pastes OM338PT and LFS-216LT were used. Algorithm incorporated into X-ray inspection system enabled to calculate the statistical distribution of LED thermal pad coverage and to find the process capability index (C_pk) of applied soldering techniques.

The evaluation of selected soldering processes of LEDs in respect of their thermal pad coverage and statistical C_pk indices is presented. Vapour-phase soldering with vacuum is capable (C_pk > 1) for OM338PT and LFS-216LT paste. Convection reflow without vacuum with LFS-216LT paste is also capable (C_pk = 1.1). Other technological soldering processes require improvements. Vacuum improves radically the capability of a reflow soldering for an LED assembly. When vacuum is not accessible, some improvement of capability to a lower extent is possible by an application of void-free solder pastes.

Six Sigma statistical methodology combined with X-ray diagnosis was used to check whether applied methods of void reduction underneath LED thermal pads are capable processes.

This paper focuses on the renewed interest in the use of condensation, or vapour‐phase, soldering in lead‐free surface mount assembly soldering and notes also the corresponding legislation, which will preclude the use of lead‐based solders in most applications by 2006. The process is once again becoming popular, because of the absolute control of soldering temperature, and because high‐quality batch and in‐line equipment is now available. It notes that condensation heating with perfluorocarbon liquids and present well‐designed equipment can be used not only in the mass‐assembly of electronic circuit boards, but also for a large variety of other heating tasks in many industries.

The purpose of this paper is to present a novel approach on the process zone characterization for direct feedback regarding the state of vapour, in order to assure a better monitoring, control and understanding of the process.

Different pressure sensors were applied in an experimental vapour phase soldering (VPS) station, where the hardware setup was dedicated to the current experiments. Static and dynamic pressure values were analyzed and correlated with additional thermal measurements.

The results reveal the dynamics of the vapour blanket generation. The correlated measurements show different stages of the process initialization, highlighting better accuracy than sole temperature measurements of saturated vapour identification. It is possible to trace the height of the available saturated vapour blanket with static pressure measurements.

The VPS process may benefit from the more precise saturation detection, giving better control on the heat transfer, enabling more efficient production with the reduction of idle time, and resulting in better soldering quality.

Reducing the idle time of the VPS stations may result in better efficiency and smaller power consumption, reducing the environmental impact of the method.

The presented methods provide a completely novel approach from the aspect of process zone state variables and parameters characterization, focusing on pressure measurements.

Soldering techniques for surface mount technology are still in their early stages. Therefore, a survey is given of the main soldering methods which are currently used in research and production as well as those which are expected to come into use, such as wave soldering, infra‐red soldering, vapour phase soldering and laser soldering. These techniques are influenced by both the component and board design. Even in soldering surface mount components, a number of rules must be observed in order to produce a good solder joint.