Lubomir Livovsky

Real-time profiling of reflow process in VPS chamber

Purpose 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. Design/methodology/approach 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. Findings 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. Originality/value 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.

Optimisation of Lead Free Solders Reflow Profile

The solder reflow profile is one of the key variables in the manufacturing process that significantly impacts product yield. In this paper we discuss the details of developing solder profiles for IR and vapor phase soldering (VPS). This paper reviews the background of smaller process windows, along with specific comparisons to common practice with tin/lead and SAC alloys. The impacts on oven set-up and operation were investigated for significant differences between these profiles. Optimal reflow profile was determined based on the number of experiments realized for tin/lead and SAC solder pastes: mechanical properties, analyze of structures and electrical properties of solder joints.

Monitoring of the temperature profile of vapour phase reflow soldering

With the introduction of lead free electronics assembly worldwide, greater concerns are raised over factory control of materials and processes. Due to the mix of both leaded and lead-free production, greater care must be introduced to ensure proper reflow process control along with data logging for product traceability. Reflow profiles must be more precise in a lead free process since the reflow temperatures of the lead free materials can approach the temperature tolerance of some of the components.

Optimization of Testing Methods for Investigation of Joints Quality Based on Vapour Phase Lead-free Soldering

Benchmarking of solder joints quality is a result of evaluation of more parameters. Solder paste and reflowed solder parameters, solder paste printing process, reflow process, components and PCBs surface finishes are the most important of them. Benchmarking the all Surface Mount Technology process with optimal techniques and methods provides a baseline of information that is key to effective process troubleshooting, manufacturability improvements and defect reduction. The developed benchmark test board features a design (the board and stencil pattern) with features for measuring solder physical, electrical and mechanical properties. Effect of different boards and components finishes, as well as effect of thermal cycling (effect of ageing) on structure and subsequently on mechanical and physical properties includes the intent of the board design. Based on these needs a comprehensive test board has been developed, which integrates testing of all the mentioned properties into a single multipurpose board design.

E-learning system and virtual laboratory for the study of electronic technologies

The paper describes the e-learning system and virtual laboratory that are intended for implementation into electrotechnology-oriented study programs. It is a short description of the main functions of the systems as well as the technologies used for the implementation.

Stability of miniaturized non-trimmed thick- and thin-film resistors

Abstract This paper is focused on reliability tests of non-trimmed miniaturized thin-film and thick-film resistors. Thick-film resistors are screen printed by polymer paste on LTCC (Low Temperature Co-fired Ceramic) substrate by two different approaches. Nonstandard precise screen printing process provide tolerance of resistivity less than 5% and thus further trimming is not necessary. OhmegaPly material with Nickel Phosphorous (NiP) metal alloy is used for thin-film resistors fabricated by subtractive process. Miniaturized resistors have dimensions 0.5 × 0.5 mm, and thus 1 square, with thickness 1 μm for thin-film and 20 μm for thick-film resistors. Stability of miniaturized resistors were tested by humidity test, thermal shocks, long-term thermal ageing, direct current stress, current pulses and simulation of soldering process using VPS (Vapour Phase Soldering). Resistivity of resistors is measured by four wire method before and after each set of test and relative change of resistivity is plotted in graphs. Influence of every test on each type of resistor is analysed.

Study of die attachment on DBC substrate

The paper describes the results of investigations concerning the behaviour and joint quality of various die attachment materials on DBC (Direct Bonded Copper) Al2O3 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 (Sn96.5Ag3.5 and Sn95.9Cu3In1Ag0.1 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.

E-learning system for Technologies in Electronics

This paper is a description of a complex e-learning system that will be implemented at the Department of Technologies in Electronics at Technical university of Košice, which should help us to increase the quality of education of the technologies in electronics. This paper is also an overview of the used technologies and planed features of the system, such as online and offline video and audio streaming, different kind of protected electronic study materials and a database of publications related to technologies in electronics.

Perspectives of CAD education at the department of technologies in electronics

The article describes the possibilities of teaching the subject “Design Systems in Electronics” (DSiE) in the second year of engineering study “Advanced materials and technology in automotive electronics”. The idea of teaching the course is the maximum engagement of students in creative activities during the study, which culminated in the presentation of the proposed work in the field of Printed Circuit Board (PCB). The resulting student work reflects the theme of the diploma work.

Bent multilayer LTCC modules for sensor applications

The potential of Low Temperature Cofired Ceramic (LTCC) multilayer technology allows to realize different structures for sensor applications. Examples of sensors realized at the Department of Hybrid Microelectronics Technical University in Kosice have shown the quality of being potential or the possibility of developing of LTCC for wide field of thick film sensor applications and for bent multi-layer LTCC modules and their application in thick film pressure sensors. LTCC is a technology suitable for design flexibility comparing with conventional thick film, thin film and high-temperature cofired technologies in electronics. Authors of this paper introduced the concept of using the bent multi-layer LTCC modules in unconventionally shaped electronic devices or in the field of sensors.