Zhihua Tao

A new approach causing the patterns fabricated by silver nanoparticles to be conductive without sintering

Silver nanoparticles (Ag NPs) with a mean size of about 90 nm were synthesized by polyol reduction of silver nitrate with ethylene glycol (EG) in the presence of poly(vinyl pyrrolidone) (PVP). The Ag NPs undergo a spontaneous coalescence in the presence of chloride ions even without a traditional sintering process which occurs at a relatively high temperature. Such behavior can cause a rapid decrease in the resistivity of the patterns fabricated by Ag NPs. Conductive silver lines were successfully fabricated on FR-4 substrate using this method. The resulting conductivity of the silver lines reached about 16% of the bulk silver value, which enables fabrication of conductive patterns on some electronic devices.

New insight into the size-controlled synthesis of silver nanoparticles and its superiority in room temperature sintering

For the better application of room-temperature sintering in printed electronics, a low-cost and convenient approach to synthesize size-controlled silver nanoparticles (Ag NPs) ca. 37 nm in average diameter is presented. Monodisperse Ag NPs with a narrow size distribution were rapidly and routinely produced on relatively large scales through a typical polyol process using poly(vinyl pyrrolidone) (PVP) as the capping agent and poly(ethylene glycol) (PEG) to enhance the reducibility and viscosity of solvent. These Ag NPs would suffer a spontaneous sintering, which was triggered by the desorption of PVP from their surface, when they encountered a certain amount of Cl−; the eventual coalescence and Ostwald ripening processes would make their structure more compact and solid, leading to a high conductivity even up to 40% that of bulk silver.

Failure mechanism of solder bubbles in PCB vias during high‐temperature assembly

Purpose – Pb‐free soldering challenged printed circuit board (PCB) assembly with high temperature. The purpose of this paper is to explain the failure mechanism of printed circuit board (PCB) assembly with solder bubbles of vias to avoid the problems of via‐drilling defects and solder joint failure.Design/methodology/approach – The failure of PCB vias with solder bubbles was investigated through cross sections and SEM microstructure inspection, TMA measurement, moisture absorption analysis and DSC measurement. The moisture absorption and CTE of FR4 laminate matched with manufacturing requirement to avoid the effects of solder bubbles. The effects of via drilling with a dull drill bit were compared to that with a new drill bit.Findings – The moisture absorbed inside holes of via plating layers could be exposed to induce solder bubbles during Pb‐free soldering assembly and dull drill bits should be prevented during the drilling process to avoid the no‐bearing drilling effects.Originality/value – The failure...

The superiority of silver nanoellipsoids synthesized via a new approach in suppressing the coffee-ring effect during drying and film formation processes

Silver nanoellipsoids (Ag NEs) with about 40 nm diameter minor axis and 100 nm major axis were prepared by a typical polyol process in the presence of poly(vinyl pyrrolidone), using Cl(-) as etching agent at the early stage of synthesis and poly(ethylene glycol) at the later stage to control the size. A suspension of these kinds of Ag NEs can resist the coffee-ring effect and deposit uniform films after drying. By contrast, suspensions of spherical silver nanoparticles suffer the coffee-ring effect badly, always leaving a ring on the edge of patterns after evaporation is complete. The reasons behind these phenomena can be mainly attributed to the long-ranged interparticle attraction between Ag NEs that preserves them from being transported by Marangoni flows during the drying process. These Ag NEs will be very useful in the preparation of conductive inks. They can perform well in the solidification process of printed patterns, forming uniform and smooth films, greatly enhancing the printing efficiency.

Effects of Mn2+ on the electrical resistance of electrolessly plated Ni-P thin-film and its application as embedded resistor

Abstract The effects of manganese sulfate monohydrate (denoted as MSM) on the properties of electroless Ni–P thin-film were investigated. The properties of Ni–P thin-film were examined by means of atomic force microscopy (AFM), cyclic voltammetry, scanning electron microscopy (SEM), X-ray diffraction, energy-dispersive X-ray spectrometer and X-ray photoelectron spectroscopy. AFM and SEM results showed that MSM had significant influences on the morphology, including the formation of smaller nodules, nano-size particles boundaries on both surface and inside of nodules. Due to the specific topologies, the resistance of Ni–P thin-film deposited with MSM was increased. Based on the characterization results, we summarized that the Mn2+ or Mn2+-compound were primarily confirmed to act as the stabilizer in Ni–P electroless process. Moreover, the verification test for Ni–P thin-film in application as embedded resistor was carried out through electrical, thermal stability examination by means of current–voltage (I–V), temperature coefficient of resistance and thermal shock tests, respectively. Experiment results demonstrated the Ni–P thin-film deposited with MSM is qualified for embedded resistors.

UV laser cutting of glass-epoxy material for opening flexible areas of rigid-flex PCB

Purpose – The purpose of this paper is to form good cutting qualities in glass-epoxy material for opening flexible areas of rigid-flex printed circuit boards (PCB) by ultraviolet (UV) laser cutting. Design/methodology/approach – The cut width and cut depth of glass-epoxy materials were both observed to evaluate their cutting qualities. The heat affected zone (HAZ) of the glass-epoxy material was also investigated after UV laser cutting. The relationships between the cut width and the parameters of various factors were analyzed using an orthogonal experimental design. Findings – The cut width of the glass-epoxy material gradually increased with the increment of the laser power and Z-axis height, while cutting speed and laser frequency had less effect on the cut width. Optimal parameters of the UV laser process for cutting glass-epoxy material were obtained and included a laser power of 6W, a cutting speed of 170 mm/s, a laser frequency of 50 kHz and a Z-axis height of 0.6 mm, resulting in an average cut wi...

Effects of MnSO4 on microstructure and electrical resistance properties of electroless Ni−P thin-films and its application in embedded resistor inside PCB

Purpose – Nickel phosphorus (Ni−P) thin-films have been electrolessly deposited in an acid-plating bath with the addition of manganese sulfate monohydrate (MSM) to achieve higher resistance for the application of embedded resistor with value beyond 10 KΩ. As this material is being used for fabricating embedded resistors under the addition of MSM, its resistance properties including effects of MSM concentration and plating time on resistances, temperature coefficient of resistance (TCR), and resistance tolerance of embedded resistor were investigated. The paper aims to discuss these issues. Design/methodology/approach – The structure of fabricated Ni−P film was detected by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The properties of substrate, including the surface morphologies, glass transition process and boundary of copper pad and substrate surface, were performed by SEM, dynamic mechanical analysis and optical microscope, respectively. The resistance toleran...