Soldering

Sintered silver joint is a porous silver that bonds a semiconductor die to the substrate as part of the packaging process. Sintered Ag is one of the few possible bonding methods to fulfill the operating conditions of wide band-gap power device technologies. We review the current technology development of sintered Ag as a bonding material from the perspective of patents filed by various stakeholders since late 1980s. This review addresses the formulation of sintered pastes (i.e. nano-Ag, hybrid Ag and micron Ag fillers), innovations in the process and equipment to form this Ag joint. This review will provide the insights and confidence to engineers, scientists from universities and industry as well as investors who are developing and commercializing the sintered Ag as a bonding material for microelectronic packaging.

Abstract
Purpose – This study aims to synthesize polyethylene glycol (PEG)-rosin derivatives from rosin and PEG for the production of solid soldering fluxes.
The PEG-rosin derivatives would be water soluble, and the resulting solid soldering fluxes would have reasonable wetting ability when combined
with a low-halide-content activator.
Design/methodology/approach – This paper presents a synthetic process for PEG-rosin derivatives. The reaction conditions (including catalyst
type, catalyst concentration, reaction temperature and PEG type) were optimized for the synthesis of PEG-rosin derivatives. The chemical and physical
properties of PEG-rosin derivatives were characterized by Fourier transform infrared spectroscopy, carbon-13 nuclear magnetic resonance
spectrometry, differential scanning calorimetry and gel permeation chromatography. The production and characteristics of water-soluble rosin fluxes
(WSRFs) were studied according to the standards of the Japanese Industrial Standards (JIS) Committees.
Findings – WSRs were successfully synthesized from rosin and PEG using 2 per cent ZnO as a catalyst, with a 2:1 molar ratio of rosin:PEG at 250°C
over 9 h. The resulting WSRs were completely soluble in water. As the PEG3000-rosin had the highest melting point (55.2°C), it was chosen for the
preparation of the WSRFs. Activators such as succinic acid, glutaric acid, ethylamine hydrochloride and diethylamine hydrobromide were selected
for use in the production of the fluxes. It was found that WSRF 09 and WSRF 04 gave the best performance with the lead-free Sn-0.7Cu solder alloy
in terms of good solderability, low halide content (less than 1,500 ppm), high insulation resistance and low corrosion. These fluxes were applied
to produce solder pastes with Sn-3.0Ag-0.5Cu alloy and they passed the performance tests as expected for solder paste.
Research limitations/implications – Further studies are necessary on large-scale production and to compare the performance of these fluxes to
those from conventional water-soluble fluxes currently available in the market. Application of these fluxes on low-temperature solder alloys such
as SnZn and SnBi (Ren et al., 2016) worth further study.
Originality/value – The classification of flux systems according to the JIS 3283 standard does not specify PEG-rosin derivatives in the flux;
nevertheless, ranking of the flux systems based on the halide content and corrosion properties of activators would be useful information when
selecting flux systems for electronics soldering in water-washable applications. The application of these fluxes in solder paste gave very promising
results and is worth investigating into more detail, as well as field test.
Keywords Flux, Sn-Ag-Cu, Solder, Solder paste, PEG-rosin, Polyethylene glycol, Rosin, Sn-Cu

Kunsthistorische, technologische und materialtechnische Analyseergebnisse
zu einem jüdischen Hochzeitsring aus Köln
A golden Jewish wedding ring from
the Cologne City Museum raises a
number of questions. The small
golden object of unknown provenance
was recently analyzed by a
qualified restorer, an art historian
and a chemist.