Juraj Durisin

VPS and reliability of solder joint

This paper deals with presentation of some new aspects of solder ternary alloy 96.5Sn3Ag0.5Cu (wt.%) - SAC305, in order to determine variations in mechanical properties and microstructure caused by treatment in vapour phase soldering (VPS) as well as by accelerated isothermal aging. These specimens have been melted and solidified on HASL (hot air solder levelling) and Ni/Au (ENIG) PCB (printed circuit board) substrate in order to prevent compositional changes due to interfacial reactions. Emphasis was placed on studying the effect of anomalous behaviours of intermetallic compounds Cu6Sn5 during ageing processes.

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.

Structure and thermal behavior of lead-free solders prepared by rapid solidification of their melt

Purpose The paper aims to investigate the structure and thermal stability of newly developed lead-free Sn-based alloys which can be used as novel materials in the soldering of electronic components. Design/methodology/approach Rapid solidification was used to prepare the alloys. Findings The results showed that the microstructure of these solders exhibited uniform distribution and small-sized intermetallic compounds. Also, smaller crystalline size can be expected compared to commercially available counterparts. The analyses revealed a uniform and homogenous distribution of the small intermetallic particles of Cu6Sn5 and Ag4Sn in the microstructure of solders. The practical implications mean an improvement in mechanical properties and thermal stability of such solder joints, which is a precondition of low mechanical, thermo-mechanical stresses in their structure. Originality/value The originality lies in the production of these alloys by the melt spinning technique which was not previously used in the electronics industry.

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.

Preparation and microstructure evolution of nanocomposite powder copper

The paper is aimed at preparing the nanocrystalline Cu-Al2O3 and Cu-MgO powders with 1-10 vol.% of the dispersoid by a combination of mechanical milling and phase precursor transformations. The secondary particles were prepared in situ within CuO powder. The nanometric Cu matrix was obtained by different reduction methods of the CuO precursor. The influence of dispersoid quantity and different technological parameters on the Cu microstructure was estimated. The study compares the microstructural evolution of Cu-3 vol.% MgO and Cu-3 vol.% Al2O3 composites. The effects of both oxides on the preservation of the initial powder nanostructure after consolidation and the thermal structural stability, as well as the tensile properties, are analysed. The results indicate that an alumina dispersoid is more suitable for nanostructure stabilisation of a Cu matrix compared to an MgO one, due to good coherency at the Cu/Al2O3interface.

Influence of firing profile on microstructural and dielectric properties of LTCC substrates

Purpose The purpose of this paper is to analyse the influence of various firing profiles on microstructural and dielectric properties of low-temperature, co-fired ceramic (LTCC) substrates in a GHz frequency range. According these analyses, sintering process can be controlled and modified to achieve better performance of devices fabricated from LTCC substrates. Design/methodology/approach Samples from LTCC substrates GreenTape 951 and GreenTape 9K7 were sintered by four firing profiles. Basic firing profile recommended by the manufacturer was modified by increasing the peak temperature or the dwell time at the peak temperature. The influence of firing profile on microstructural properties was analysed according to measurements by X-ray diffractometer (application of the Cu K-alpha radiation and the Bragg-Brentano method), and the influence on dielectric properties (dielectric constant and dielectric losses) was analysed according to measurements by split cylinder resonator method at 9.7 and 12.5 GHz. Findings Rising of the peak temperature or extension of dwell time at this temperature has influence on all analysed properties of LTCC substrates. Size of crystallites can be changed by modification of firing profile as well as microdeformation. In addition, dielectric properties can be changed too by modification of the firing profile. Correlation between microdeformation and dielectric losses was observed. Originality/value The novelty of this work lies in finding the mutual relationship between changes in microstructural (size of grains and microdeformation) and dielectric properties (dielectric constant and dielectric losses) caused by different firing profiles.

Analysis of intermetallic compounds in lead-free solders

Intermetallic compounds (IMCs) are essential part of lead-free solders microstructure. In 96.5Sn3Ag0.5Cu (SAC305) solder is dominant element tin (Sn). But despite this Sn dominancy only 3% weight contain of silver (Ag) has influence on final structure of solid solder joint. Fundamental impact on strength properties of solder joint has also interaction between the solder and printed circuit board (PCB) pad. Another important factor is effect of ageing process. Analysis of presence of IMCs in solder joints is essential key to understand behaviour of the lead-free solder joints.

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.

Influence of current and combined thermo-current load on microstructure and resistance of solder joints

The aim of our work is to evaluate an influence of current and combined thermo-current load on microstructure and electrical resistance of solder joints. The solder joints formed on bare Cu printed circuit board pads were long-term loaded by large current and high temperature. The obtained results clearly show that the both load methods significantly affect microstructure and electrical resistance of the joints. The both loads lead to a formation of extensive voids in the solder joints due to the effect of electromigration thus causing evident increase of their resistance. The resistance increase is more significant for the joints loaded by the combined thermo-current load.

Influence of different methods of ageing on microstructure of solder joints

An influence of damping heat and thermal cycling on microstructure and microhardness of solder joints was investigated. Solder joints were prepared by vapour phase and hot air reflow soldering. Results of the microstructure analysis show on significant influence of the ageing on propagation of voids and cracks in the bulk of solder joints.