Shouxu Wang

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.

Preparation of High-Performance Conductive Ink with Silver Nanoparticles and Nanoplates for Fabricating Conductive Films

A novel preparation method for a high-performance conductive ink which consisted of silver nanoplates, spherical silver nanoparticles, and epoxy resin was developed. Silver nanoparticles and nanoplates were synthesized via chemical reduction method in the presence of poly (vinyl pyrrolidone) (PVP). The prepared silver ink exhibited a remarkable electrical, thermal stability, and mechanical properties, which were confirmed by the four-point probe method, thermogravimetric analysis (TGA), and the three-point bending testing. We demonstrated the influence of sintering temperatures and time on the electrical resistivity. After sintering at 150°C for 15 min, the conductive film was able to achieve the volume electrical resistivity of (3–4) × 10−5Ω · cm.

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.

Multiphysics coupling simulation of RDE for PCB manufacturing

Purpose – The purpose of this paper is to optimize experimental parameters and gain further insights into the plating process in the fabrication of high-density interconnections of printed circuit boards (PCBs) by the rotating disc electrode (RDE) model. Via metallization by copper electrodeposition for interconnection of PCBs has become increasingly important. In this metallization technique, copper is directly filled into the vias using special additives. To investigate electrochemical reaction mechanisms of electrodeposition in aqueous solutions, using experiments on an RDE is common practice. Design/methodology/approach – An electrochemical model is presented to describe the kinetics of copper electrodeposition on an RDE, which builds a bridge between the theoretical and experimental study for non-uniform copper electrodeposition in PCB manufacturing. Comsol Multiphysics, a multiphysics simulation platform, is invited to modeling flow field and potential distribution based on a two-dimensional (2D) ax...

Producing fine pitch substrate of COF by semiadditive process and pulse reverse plating of Cu

Abstract On the chip on film (COF) substrate, the width of the conductor of the substrate is usually smaller than 50 μm, with the smallest ones being 15 μm. It is difficult to produce it by the conventional subtractive process. In this study, the semiadditive process has been used to produce fine pitch substrates of COF. The flexible copper clad laminate (FCCL) used in the semiadditive process is a copper foil that is 2 μm thick; the FCCL with 8 μm thick copper foil is used to produce the same substrate of a COF by the conventional subtractive process. The effects of the semiadditive process and subtractive process have been studied and compared. Two sample substrates (50 μm/50 μm and 30 μm/30 μm fine pitch) have been designed. H2SO4/H2O2 etchant has been used in the etching process for the semiadditive process successfully. The test results of the metallographic slicing tester and the SEM show that the semiadditive process is more suitable to produce fine pitch pattern (below 50 μm/50 μm) than the subtractive process, especially in the application that requires an accurate impedance. In addition, the periodic pulse reverse plating can improve the thickness uniformity and physical properties of the electroplated copper layer.

Synthesis and characterization of Ag nanorods used for formulating high-performance conducting silver ink

Silver nanorods with ∼100 nm in diameter and ∼5 µm in length were synthesised by the soft solution-phase approach in the presence of poly(vinylpyrrolidone) (PVP), which was employed as a protecting agent. The obtained silver nanorods were characterised by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV-visible spectrum. The molar ratio and injection rate of PVP and AgNO3 played an important role in controlling the morphology and aspect ratio of nanorods. The growth mechanism of silver nanorods was also discussed. Moreover, the conductive ink was prepared using as-synthesised products, and the electrical resistivity of the final consolidated trace with this kind of ink was up to 2.7 × 10−5 Ωcm.

Study on brown oxidation process with imidazole group, mercapto group and heterocyclic compounds in printed circuit board industry

The adhesion strength of the interface between copper foil and resin is an important technological parameter for applications in microelectronics. In this study, a new brown oxidation solution of copper foil, including the recipe composition and reliability tests, was fully discussed. We provided an overview of brown oxidation process used in the semi-flexible printed circuit boards production industry by investigating the brown oxide film. The morphology of the copper oxide film was changed from lamellar structure to honeycomb structure with the increasing of oxidation time. The peel adhesion strength of the Cu/polyimide laminates was increased from about 2–16 N/cm by altering the immersion time and the concentration of inhibitors in brown oxidation solution. Scanning electron microscopy, peel tests and X-ray diffraction indicated that the higher adhesion strength was resulted from the rougher surface and the proper etching depth of copper foil, which was caused by chemical reactions on the interface surface of copper foil.

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.

A Novel Nitric Acid Etchant and Its Application in Manufacturing Fine Lines for PCBs

We have developed a new etching solution for the printed circuit board industry. The primary oxidant of the solution is nitric acid, which reacts with copper coating on the substrate. The other components of the solution are sulfuric acid and additive, which are used to control etching reaction rate and solutions characteristics. The optimum parameters for the concentrations of nitric acid, sulfuric acid, additive, and the operating temperature were obtained through orthogonal experiment with stagnant etching method. The parameters were then verified by the spray etching experiment in the industrial production line. Then, there are a series of tests, carried out by metallographic slicing tester and scanning electron microscopy to evaluate the quality of copper conductive lines in stagnant and spray etching experiments. compared with conventional cupric chloride etchant, the testing results showed that the nitric acid etchant can manufacture fine lines with lower undercut, better wall sides, with higher etching rate, as well as being more friendly to the environment How the addition of H2SO4 influences etching rate and etching mechanism of nitric acid etchant is also discussed.

Multi-physics coupling aid uniformity improvement in pattern plating

Purpose The uniformity of electrodeposition is the key to successful application of pattern plating because the quality of electrodeposited copper layer has a huge impact on the performance of printed circuit boards (PCBs). The multi-physics coupling technology was used to accurately analyze and forecast the characteristics of electrochemical system. Further, an optimized plating bath was used to achieve a uniform electrodeposition. Design/methodology/approach A multi-physics coupling numerical simulation based on the finite element method was used to optimize electrodeposition conditions in pattern plating process. The influences of geometric and electrochemical factors on uniformity of current distribution and electrodeposited layer thickness were discussed by multi-physics coupling. Findings The model results showed that the distance between cathode and anode and the insulating shield had a great impact on uniformity of electrodeposition. By numerical simulation, it had been proved that using an auxiliary cathode was an effective and simple way to improve uniformity of electrodeposition due to redistributing of the current. This helped to achieve more uniform surface of the copper patterns by preventing the edge effect and the roughness of the copper layer was reduced to 1 per cent in the secondary current distribution model. Research limitations/implications The research is still in progress with the development of high-performance computers. Practical implications A multi-physics coupling platform is an excellent tool for quickly and cheaply studying the process behaviors under a variety of operating conditions. Social implications The numerical simulation method has laid the foundation for the design and improvement of the plating bath. Originality/value By multi-physics coupling technology, we built a bridge between theoretical and experimental study for control of uniformity of pattern plating in PCB manufacturing. This method can help optimize the design of plating bath and uniformity of pattern plating in PCB manufacturing.