Search results

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.

Vapor phase soldering (VPS), also known as condense soldering, is capable of improving the mechanical reliability of solder joints in electronic packaging structures. The paper aims to discuss this issue.

In the present study, VPS is utilized to assemble two typical packaging types (i.e. ceramic column grid array (CCGA) and BGA) for electronic devices with lead-containing and lead-free solders. By applying the peak soldering temperatures of 215°C and 235°C with and without vacuum condition, the void formation and intermetallic compound (IMC) thickness are compared for different packaging structures with lead-containing and lead-free solder alloys.

It is found that at the soldering temperature of 215°C, CCGA under a vacuum condition has fewer voids but BGA without vacuum environment has fewer voids despite of the existence of lead in solder alloy. In light of contradictory phenomenon about void formation at 215°C, a similar CCGA device is soldered via VPS at the temperature of 235°C. Compared with the size of voids formed at 215°C, no obvious void is found for CCGA with vacuum at the soldering temperature of 235°C. No matter what soldering temperature and vacuum condition are applied, the IMC thickness of CCGA and BGA can satisfy the requirement of 1.0–3.0 µm. Therefore, it can be concluded that the soldering temperature of 235°C in vacuum is the optimal VPS condition for void elimination. In addition, shear tests at the rate of 10 mm/min are performed to examine the load resistance and potential failure mode. In terms of failure mode observed in shear tests, interfacial shear failure occurs between PCB and bulk solder and also within bulk solder for CCGA soldered at temperatures of 215°C and 235°C. This means that an acceptable thicker IMC thickness between CCGA solder and device provides greater interfacial strength between CCGA and device.

Due to its high I/O capacity and satisfactory reliability in electrical and thermal performance, CCGA electronic devices have been widely adopted in the military and aerospace fields. In the present study, the authors utilized VPS to assemble a typical type of CCGA with the control package of conventional BGA to investigate the relation between essential condition (i.e. soldering temperature and vacuum) to void formation.

The opportunity for mutual benefit across Europe to develop low‐cost MCM technologies arose from recognition of the scientific skills and design and prototyping capabilities in organic and inorganic circuits in countries of Central Europe. As a result, the leading research institutions and small/medium‐size enterprises of Hungary, Romania and Slovenia together with relevant institutions of the UK and Belgium proposed and received approval for a European Union INCO‐Copernicus project “Cheap multichip models” to establish fast prototyping low cost multichip module (MCM) technology facilities. The project commenced in May 1997.

This paper aims to present a new method of real-time monitoring of thermal profiles applied in vapour phase soldering (VPS) reflow processes. The thermal profile setting is a significant variable that affects the quality of joints. The method allows rapid achievement of a required thermal profile based on software control that brings new efficiency to the reflow process and enhanced joint quality, especially for power electronics.

A real-time monitoring system based on computerized heat control was realized in a newly developed laboratory VPS chamber using a proportional integral derivation controller within the soldering process. The principle lies in the strictly accurate monitoring of the real defined reflow profile as a reference.

Very accurate maintenance of the required reflow profile temperature was achieved with high accuracy (± 2°C). The new method of monitoring and control of the reflow real-time profiling was verified at various maximal reflow temperatures (230°C, 240°C and 260°C). The method is feasible for reflowing three-dimensional (3D) power modules that use various types of solders. The real-time monitoring system based on computerised heat control helped to achieve various heights of vapour zone.

The paper describes construction of a newly developed laboratory-scale VPS chamber, including novel real-time profiling of the reflow process based on intelligent continuously measured temperatures at various horizontal positions. Real-time profiling in the laboratory VPS chamber allowed reflow soldering on 3D power modules (of greater dimensions) by applying various flux-less solder materials.

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.

Atmospheric dependent, gas sensitive resistors seem to be good candidates for detecting critical air pollution levels. Recently, great progress has been made in the development of various sensor types, but less attention seems to be paid to the integration of sensor elements with different characteristics. The aim of this international project is to develop a smart hybrid gas multi‐sensor module for environmental applications, i.e. by combining classical thick‐ and thin‐film elements with polymer‐film based sensors and also a signal processing ASIC within a single package, which should be useful for all sensor types. The module should enable multi‐sensor operation as well, when connected to an intelligent signal‐processing unit.

The paper aims to present an investigation of heating during vapour phase soldering (VPS) on inclined printed circuit board (PCB) substrates. The PCB is a horizontal rectangular plate from the aspect of filmwise condensation with a given inclination setting.

The paper focuses on the measurement of temperature distribution on the PCBs with a novel setup immersed in the saturated vapour space. The measuring instrumentation is optimized to avoid and minimize vapour perturbing effects.

The inhomogeneity of the heating is presented according to the lateral dimensions of the PCB. The inclination improves temperature uniformity, improves heat transfer efficiency; however, a minor misalignment may affect the flow and result in uneven heating.

The results can be implemented for practical improvements in industrial ovens with the use of intended inclination. The improvements may consequently point to more efficient production and better joint quality.

The novel method can be used for deeper investigation of inclination during and can be complemented with numerical calculations. The results highlight the importance of precise PCB holding instrumentation in VPS ovens.

The purpose of the paper is to improve the control of vapour phase soldering (VPS). To enable better productivity and assembling quality, the industry needs to provide precise control and measurements during assembling. In the paper, a special monitoring method is presented for VPS to enable improved process control and oven state identification.

The work presents the investigation of the workspace with dynamic and gage type pressure sensors in fusion with thermocouples. Different sensors were evaluated to find an appropriate type. The relation between the temperature and the pressure was investigated, according to the setup of the oven. The effect of inserting a printed circuit board (PCB) on the pressure of the vapour inside the oven was also investigated with the pressure/power functions.

It was found that the novel gage-type sensors enable better precision than solutions seen in previous literature. The sensors are able to monitor the decreasing vapour concentration when a PCB is inserted to the workspace. It was found that there is a suggested minimum power to sustain a well-developed vapour column for soldering in saturated vapour. An inflexion point highlights this in the pressure/power function, in accordance with the temperature/power curve.

The research presents original works with aspects of a novel sensor fusion concept and work space monitoring for better process control and improved soldering quality.

The purpose of this paper is to compare the reliability and intermetallic layer (IML) of solder joints prepared with infrared (IR) and vapour phase (VP) soldering. The reliability of 0603-sized resistors’ solder joints formed with IR and VP soldering was investigated. The IML of the joints was analysed based on image processing algorithm automatically.

For the reliability analyses, the ageing method was a highly accelerated stress test (HAST) with +105°C maximum temperature, fully saturated (100 per cent) relative humidity at +0.5 atm overpressure. The joints were characterised based on the thickness of their IML and on their shear strength in as-reflowed stage, and after 400, 800, 1,200, 1,600 and 2,000 hours of HAST. An image processing algorithm was developed to measure the thickness of the IMLs on cross-sectional scanning electron microscopy (SEM) images automatically.

The increase of the IML thickness is lower in the case of HAST ageing compared to other methods. The thickness increment of the Cu₆Sn₅ layer was higher for IR and lower for VP soldering; the Cu₃Sn layer cannot be inspected even after 2,000 hours of HAST ageing. The results of shear strength measurements show better reliability for VP soldered joints.

The developed image processing method is applicable to obtain quantitative results about the IMLs in an effective fast way.

There is a lack of information in the literature regarding the reliability comparison of solder joints formed with VP and conventional reflow processes. Thus, we performed research about the lifetime of solder joints formed with VP and IR reflow method.