Reflow of Sn-3.8Ag-O.7Cu solder on Ni substrate in presence of Mo nanoparticles

In this study, Mo nanoparticles were used as a reinforcing material into the Sn-3.8Ag-0.7Cu (SAC) solder on the nickel (Ni) substrate electrodeposited on polycrystalline copper (Cu) sheets. The Mo nanoparticles were characterized by transmission electron microscopy (TEM) and X-ray diffractometer (XRD). The composite solder pastes were prepared by manual mixing of Mo nanopartic1es with the SAC solder paste. Ni layer was electrodeposited on polycrystalline Cu substrate by using the Watts bath. The solder paste was placed on the substrate by following the Japanese Industrial Standard (nS) and reflowed up to six times at 250°C for 45 seconds. After first reflow, elemental compositions of the nanocomposite solders were analyzed by inductively coupled plasma-optical emission spectrometer (ICP-OES). The spreading rate and wetting angle of the solder were determined after first reflow. Microstructural investigations at the solder joints were carried out by using high resolution field emission scanning electron microscope (FESEM) and energy dispersive X-ray (EDX). Results reveal that after reflow only a fraction of Mo nanoparticles were retained inside the solder matrix. Mo nanoparticles are effective in suppressing the growth of total IMC layer and scallops during reflow. The retardation of IMC thickness and scallop diameter is suggested due to the discrete particle effect of Me nanoparticles

Implementation of micro-level problem based learning in a course on electronic materials

Accreditation bodies for engineering education around the world have been advocating for the implementation of outcome based education. In order to achieve this effectively, engineering educators are increasingly adopting student-centered modes of learning. One such mode is problem based learning (PBL). In this paper experience with the implementation of micro-level PBL is described. Here one topic in a course on electronic materials at the undergraduate programme in materials engineering is taught using PBL. At the end of the course, students feedback is recorded to gauge the success or otherwise of this learning method. In general, student are found to be more enthuiastic in learning with PBL than in lectures. They appreciated to have, in the PBL, an opportunity to play the role of a professional engineer and to apply acquired kowledge to solve a particular problem. Student feedback reveals that PBL can be effective in achieving the programme outcomes (POs) that are not easy to achieve through lectures, such as those related to i) lifelong learning, ii) team work, iii) professional and ethical responsibility, iv) economic, social and environmental impact, etc.. Thus PBL can complement lectures in successfully implementing outcome based education. Implementation of PBL at the micro level, that is, for one topic in a course has been found to be fairly easy as it does not require any extra resources. Since converting the whole undergraduate programme into PBL can be a formidable venture, it is believed that PBL can be adopted for a limited number of topics in some of the major courses in the programme with tangible benefits

Effects of addition of copper particles of different size to Sn-3.5Ag solder

In this study, copper particles with different sizes 20-30 nm, 3 and 10 mu m were incorporated into Sn-3.5Ag solder paste to form Sn-Ag-Cu composite solder. The Cu particles were added at 0.7 and 3 by paste mixing for 30 min. The composite solder samples were prepared on copper substrate at 240A degrees C for 60 s. Differential scanning calorimetry was conducted to measure the melting point of the composite solder. The wetting angle and microstructure of the composite solder were studied using optical microscope and scanning electron microscope. Micro hardness was measured using a 10 gf load. It was reported that the lowest melting point was obtained at 216.3A degrees C when Cu nanoparticles was added at 3 to Sn-3.5Ag. The microstructure of Sn-3.5Ag solder structure was dendritic in nature. With the addition of Cu nanoparticles, the microstructures were modified with more refined Sn structures. The existence of sunflower morphology of un-melted copper was observed when Cu microparticles were added

Effect of Pedestal Temperature on Bonding Strength and Deformation Characteristics for 5N Copper Wire Bonding

In recent years, copper has increasingly been used to replace gold to create wire-bonded interconnections in microelectronics. While engineers and researchers in the semiconductor packaging field are continuously working on this transition from gold to copper wires to reduce costs, the challenge remains in producing robust and reliable joints for semiconductor devices. This research paper investigates the effect of pedestal temperature on bonding strength and deformation for 99.999% purity (5N) copper wire bonding on nickel-palladium-gold (NiPdAu) bond pads. With increasing pedestal temperature, significant thinning of the copper ball bond can be achieved, resulting in higher as-bonded ball shear strengths while producing no pad damage. This can be helpful for low-k devices with thin structures, so as to prevent the use of excessive bond force and ultrasonic energy during copper wire bonding

Effects of Co nanoparticle addition to Sn-3.8Ag-0.7Cu solder on interfacial structure after reflow and ageing

Effects of Co nanoparticle additions to Sn-3.8Ag-0.7Cu on the structure of solder/copper interface have been studied after reflow and high temperature ageing (150 degrees C, up to 1008 h). Results show that the Co nanoparticles substantially suppress the growth of Cu(3)Sn but enhance Cu(6)Sn(5) growth. Cobalt nanoparticles reduce interdiffusion coefficient in Cu(3)Sn. It is suggested that the Co nanoparticles undergo surface dissolution during reflow and exert their influence, at least partially, through alloying effect. (C) 2011 Elsevier Ltd. All rights reserved

Influence of laser power on bonding strength for low purity copper wire bonding technology

The drive for improving copper wire bonding has been more rampant with continued rise in gold prices. The global increase in gold price directly resulted the semiconductor packaging industry to rapidly replace gold as a medium of interconnection to copper wire. This is a cost effective solution for creating viable interconnections for integrated circuit packaging. However, through past research it is well known the hardness of copper wire is significantly higher compared to gold wire and the usage of copper poses various challenges in electronic packaging. These challenges, resulting from the usage of copper wire is primarily due to the high hardness of copper. Higher hardness of copper as compared to gold will require higher bonding force and ultrasonic energy to create bonding to the bond pads. The higher bonding force makes copper wire bonding unsuitable for fragile structures and possible damage to underlying circuitry. Past research has also exhibited the hardness of copper wire decreases as the purity levels increase, however the usage of higher purity copper wires in high volume manufacturing may significantly increase manufacturing cost. This research therefore investigates the application of laser assisted heating for enabling improved copper wire bonding strength and improved grain structures for low purity copper wires. Experimentations were conducted accordingly on three copper wire purity types, 99.9% purity (3 N), 99.99% purity (4 N) and 99.999% purity (5 N) copper wires, so as to evaluate the impact of laser assisted heating on various copper purity levels. The result of this study shows laser assisted heating is able to improve the bonding strength and improve the grain structure by means of reduced columnar grains for copper wires with lower purity levels. It is shown, higher as-bonded ball shear strengths with fewer columnar grains were observed when the highest laser heating intensity was applied. The results of this study can be helpful for integrated circuit packaging especially to enable interconnections using copper wire materials with lower purity levels, enabling a more cost effective manufacturing. © 2019 Elsevier B.V

Soldering Characteristics and Mechanical Properties of Sn-1.0Ag-0.5Cu Solder with Minor Aluminum Addition

Driven by the trends towards miniaturization in lead free electronic products, researchers are putting immense efforts to improve the properties and reliabilities of Sn based solders. Recently, much interest has been shown on low silver (Ag) content solder SAC105 (Sn-1.0Ag-0.5Cu) because of economic reasons and improvement of impact resistance as compared to SAC305 (Sn-3.0Ag-0.5Cu. The present work investigates the effect of minor aluminum (Al) addition (0.1–0.5 wt.%) to SAC105 on the interfacial structure between solder and copper substrate during reflow. The addition of minor Al promoted formation of small, equiaxed Cu-Al particle, which are identified as Cu3Al2. Cu3Al2 resided at the near surface/edges of the solder and exhibited higher hardness and modulus. Results show that the minor addition of Al does not alter the morphology of the interfacial intermetallic compounds, but they substantially suppress the growth of the interfacial Cu6Sn5 intermetallic compound (IMC) after reflow. During isothermal aging, minor alloying Al has reduced the thickness of interfacial Cu6Sn5 IMC but has no significant effect on the thickness of Cu3Sn. It is suggested that of atoms of Al exert their influence by hindering the flow of reacting species at the interface

Studies on electrodeposition behavior of Sn–Bi alloys in plating baths modified by hydroquinone and gelatin

This work focuses on the investigation of the electrochemical behavior of Sn–Bi plating bath modified by two electrolyte additives, hydroquinone (HQ) and gelatin. Electrochemical studies were carried out by low sweep rate polarization scans, as well as cyclic voltammetry at different scan rates (1–40 mV/s). Polarization scans at sweep rate of 1 mV/s indicate that Bi deposits at about −25 to −45 mV while Sn deposits at about −410 to −420 mV in the plating bath without additives or with either one of the additives. The addition of HQ suppresses hydrogen evolution to more electronegative potentials, showing its adsorption capabilities. On the other hand, gelatin shifts the deposition potential of Bi and is suggested to have a mild complexing effect with Bi ions. The synergistic effect of both HQ and gelatin reduces the potential gap between Bi and Sn from 429 to 255 mV. Investigations on single metallic Sn and Bi plating baths at varying sweep rates reveal different behavior of Sn and Bi ions. The shifting and broadening of Bi cathodic peak potential upon HQ + gelatin addition suggest the formation of HQ–gelatin complex species. Surface morphology and composition analyses were conducted on electrodeposits from each plating bath. Near-eutectic Sn–Bi alloy was successfully electrodeposited from the plating bath modified by HQ + gelatin

Improving mechanical and electrical properties of Cu/SAC305/Cu solder joints under electromigration by using Ni nanoparticles doped flux

The electromigration (EM) degrades the structural, mechanical and electrical properties of solder joints. An effort has been made to investigate the effects of the Ni nanoparticles (NP) doped flux on the mechanical properties and electrical resistance of SAC305 solder joints subjected to EM. SAC305 solder joints were prepared using NP-doped flux. A current density of 3 × 103 A/cm2 was applied to the joints at a constant temperature of 150 °C. Tensile tests were performed before and after the EM tests. Results reveal that after the addition of Ni NP-doped flux, the mechanical strength improved before and after EM. After EM, the fracture path for doped solder joint did not migrate to the cathode side as compared to un-doped solder. Ni NP also improved the electrical resistance and lifetime of the solder joint. The use of Ni NP-doped flux thus minimized the effects of EM and improved the mechanical and electrical performance of the solder joints

Preparation and low-temperature sintering of cu nanoparticles for high-power devices

One of the fundamental requirements for high-temperature electronic packaging is reliable silicon attach with low and stable electrical resistance. This paper presents a study conducted on Cu nanoparticles as an alternative lead-free interconnect material for high-temperature applications. Cu nanoparticles were prepared using pulsed wire evaporation technique in water medium. Pure Cu nanoparticles without any organic mixture were used in this paper. An economical approach to extract the nanoparticles from water was established. In situ Cu nanoparticles oxide reduction was successfully done using forming gas (N-2-5 H-2). Cross-section analysis on bonded interface shows onset of Cu nanoparticles sintering at 400 degrees C. We successfully demonstrated the possibilities of using Cu nanoparticles as silicon die attach material for high-temperature electronic devices