Ahmed Sharif

Comparative Study of the Dissolution Kinetics of Electrolytic Ni and Electroless NiP Layers by Molten Sn3.5Ag Solder Alloy

Journal of Electronic Packaging, 2005

Lead-free solders have high Sn content and high melting temperature, which often cause excessive ... more Lead-free solders have high Sn content and high melting temperature, which often cause excessive interfacial reactions at the interface. Sn3.5Ag0.5Cu lead-free solder alloy has been used to identify its interfacial reactions with two-metal layer flexible substrates. In this paper we investigate the dissolution kinetics of Sn3.5Ag0.5Cu solder on electrolytic Ni/electroless NiP layer. It is found that during 1 min of reflow electroless NiP layer dissolves slightly lower than the electrolytic Ni due to the barrier layer formation between the intermetallic compounds (IMCs) and electroless NiP layer. Faster nucleation of IMCs on the electrolytic Ni layer is proposed as the main reason for higher initial dissolution. The appearance of P-rich Ni layer acts as a diffusion barrier layer between the solder and electroless NiP layer, which decreases the dissolution rate and IMCs growth rate than that of the electrolytic Ni layer, but weaken the interface and reduces the ball shear strength and reliability. After acquiring certain thickness P-rich Ni layer breaks and increases the diffusion rate of Sn and as a consequence both the IMCs growth rate and dissolution rate also increases. It is found that 3 lm thick electroless NiP layer cannot protect the Cu layer for more than 120 min at 250°C. In electrolytic Ni shear strength does not change significantly and lower dissolution rate and more protective for Cu layer during long time molten reaction.

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Liquid and solid state interfacial reactions of Sn–Ag–Cu and Sn–In–Ag–Cu solders with Ni–P under bump metallization

Thin Solid Films, 2006

In this study, interfacial reactions of electroless Ni(P) metallization of the ball-grid-array (B... more In this study, interfacial reactions of electroless Ni(P) metallization of the ball-grid-array (BGA) substrate with the Sn-4 Ag-0.5 Cu (SAC405), Sn-3 Ag-0.5 Cu (SAC305) and Sn-9 In-3.5 Ag-0.5 Cu (SIAC) (wt.%) solder alloy were investigated, focusing on identification of the intermetallic compound (IMC) phases, the IMC growth rates and the consumption rate of the metallization layer at various liquid and solid state heat treatment conditions, e.g. extended reflow and solid state aging. A fixed volume of BGA solder ball (760 Am diameter) was used on a substrate metallization pad with a diameter of 650 Am. The consumption of the electroless Ni(P) in SIAC solder was also lower than in the SAC solders. The presence of indium in the solder played a major role in inhibiting the consumption of Ni(P) in the soldering reaction. The stable IMCs initially formed at the interface of the Ni(P)/In-containing solder system was the (Cu, Ni) 6 (Sn, In) 5 phase. During further reflow, the (Cu, Ni) 3 (Sn, In) 4 IMC started forming because of the limited Cu content in the solder. Bulk of the SIAC solder also contained Cu 6 (Sn, In) 5 and Ag -In -Sn precipitates embedded in the Sn-rich matrix. It was also found that more Ag-containing SAC405 solder shows higher Ni(P) consumption than SAC305 solder at the same heat treatment condition. D

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Dissolution kinetics of BGA Sn–Pb and Sn–Ag solders with Cu substrates during reflow

Materials Science and Engineering B-advanced Functional Solid-state Materials, 2004

An investigation has been carried out to compare the dissolution kinetics of the Cu pad of the ba... more An investigation has been carried out to compare the dissolution kinetics of the Cu pad of the ball grid array (BGA) substrate into the molten conventional Sn-Pb solder and Sn-3.5Ag solder. A fixed volume of the BGA solder ball (760 m diameter) was used on the 15-18 m thick Cu pad having a circular area with a diameter of 650 m. The dissolution measurement was carried out by measuring the change of Cu pad thickness as a function of time and temperature. A scanning electron microscope (SEM) was used to observe the microstructure of the solder joint and to measure the consumed thickness of Cu. A fast dissolution of the substrate occurred in the beginning for the molten solder/solid Cu reaction couple. But the dissolution in Sn-Ag was much more higher than that in Sn-Pb solder. The rates of Cu dissolution were measured for different soldering temperatures ranging from 225 to 240 • C and activation energies of 54 and 116 kJ/mol were found for the dissolution reaction in Sn-Ag and Sn-Pb solder, respectively.

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Effect of substrate metallization on interfacial reactions and reliability of Sn–Zn–Bi solder joints

Microelectronic Engineering, 2007

The scope of this paper covers a comprehensive study of the lead-free SnZnBi solder system, on ... more

The effect of curing on the performance of ACF bonded chip-on-flex assemblies after thermal ageing

Soldering & Surface Mount Technology, 2005

Purpose -Anisotropic conductive film (ACF) is now an attractive technology for direct mounting of... more Purpose -Anisotropic conductive film (ACF) is now an attractive technology for direct mounting of chips onto the substrate as an alternative to leadfree solders. However, despite its various advantages over other technologies, it also has many unresolved reliability issues. For instance, the performance of ACF assembly in high temperature applications is questionable. The purpose of this paper is to study the effect of bonding temperatures on the curing of ACFs, and their mechanical and electrical performance after high temperature ageing. Design/methodology/approach -In the work presented in this paper, the curing degree of an ACF at different bonding temperatures was measured using a differential scanning calorimeter. The adhesion strength and the contact resistance of ACF bonded chip-on-flex assembly were measured before and after thermal ageing and the results were correlated with the curing degree of ACF. The ACF was an epoxy-based adhesive in which Au-Ni coated polymer particles were randomly dispersed. Findings -The results showed that higher bonding temperatures had resulted in better ACF curing and stronger adhesion. After ageing, the adhesion strength increased for the samples bonded at lower temperatures and decreased for the samples bonded at higher temperatures. ACF assemblies with higher degrees of curing showed smaller increases in contact resistance after ageing. Conduction gaps at the bump-particle and/or particle-pad interfaces were found with the help of scanning electron microscopy and are thought to be the root cause of the increase in contact resistance. Originality/value -The present study focuses on the effect of bonding temperatures on the curing of ACFs, and their adhesion strength and electrical performances after high temperature ageing. The results of this study may help the development of ACFs with higher heat resistance, so that ACFs can be considered as an alternative to lead-free solders.

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Effect of 9 wt.% in addition to Sn3.5Ag0.5Cu solder on the interfacial reaction with the Au/NiP metallization on Cu pads

Journal of Alloys and Compounds, 2005

Sn-based lead-free solders have a high melting temperature, which often cause excessive interfaci... more Sn-based lead-free solders have a high melting temperature, which often cause excessive interfacial reactions at the interface. A small amount of In is added to reduce the melting temperature and to change the intermetallic compound (IMC) phases. Sn3.5Ag0.5Cu and Sn3.5Ag0.5Cu9In lead-free solder alloys have been used to identify its interfacial reactions with 2-metal layer flexible substrates. In this paper we investigate the effect of 9 at.% In addition to Sn3.5Ag0.5Cu solder during extended reflow. During reflow, Au diffuses rapidly in the molten Sn Ag Cu solder and forms AuSn 4 IMC but in the case of In-containing solder, In Sn Au IMCs form and are uniformly distributed in the solder. Some In Sn Au IMCs have been entrapped in the Sn Cu Ni In quaternary intermetallic compounds (QIMCs) due to lower diffusion rate of Au in the In-containing solder. Initially Sn Cu Ni ternary intermetallic compounds (TIMCs) and Sn Cu Ni In QIMCs form at the interface, which have higher growth rate and consume more of the NiP layer. Low-Cu QIMCs are found in the In-containing solder after 30 min reflow which are more stable in the P-rich Ni layer and significantly reduce the dissolution rate of the NiP layer. The spalling of Sn Cu Ni TIMCs in the Sn Ag Cu solder increases the diffusion rate of Sn atoms and as a consequence both the TIMCs growth rate and dissolution rate of the NiP layer also increases. In-containing solder have lower growth rate of the QIMCs and lower dissolution rate of the NiP layer than the Sn Ag Cu solder. Consumption of the NiP layer can be reduced by adding In, because of the formation of QIMCs at the interface, QIMCs are stable and are well adhering to the P-rich Ni layer during reflow.

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Interfacial reactions on electrolytic Ni and electroless Ni(P) metallization with Sn–In–Ag–Cu solder

Journal of Alloys and Compounds, 2005

In this study, interfacial reactions of electrolytic Ni and electroless Ni(P) metallization of th... more In this study, interfacial reactions of electrolytic Ni and electroless Ni(P) metallization of the ball-grid-array (BGA) substrate with the molten Sn-9In-3.5Ag-0.5Cu (wt.%) solder alloy were investigated, focusing on identification of the intermetallic compound (IMC) phases and the IMC growth rates at various reflowing times. A fixed volume of BGA solder ball (760 m diameter) was used on a substrate metallization pad with a diameter of 650 m. The peak reflow temperature was fixed at 240 • C while the reflow time was varied between 1 and 120 min. The intermetallic compounds thickness was lower on the electroless Ni(P)/solder interface. The consumption of the electroless Ni(P) in Sn-9In-3.5Ag-0.5Cu was also lower than that of the electrolytic Ni. The appearance of a P-rich Ni layer at the interface played a major role in inhibiting the overall interfacial reaction in the soldering reaction with the electroless Ni(P) metallization. The stable IMC initially formed at the interface was the (Cu, Ni) 6 (Sn, In) 5 phase. During further reflowing, the (Cu, Ni) 3 (Sn, In) 4 IMC started forming because of the limited Cu content in the solder. These bright low-Cu IMCs appeared earlier at the interface of the Ni/solder system than the Ni(P)/solder system. Bulk of the Sn-9In-3.5Ag-0.5Cu solder contained Cu 6 (Sn, In) 5 , Au-In-Sn and Au-In-Sn precipitates embedded in the Sn-rich matrix.

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Comparative study of the dissolution kinetics of electrolytic Ni and electroless NiP by the molten Sn3.5Ag0.5Cu solder alloy

Microelectronics Reliability, 2003

Lead-free solders have high Sn content and high melting temperature, which often cause excessive ... more Lead-free solders have high Sn content and high melting temperature, which often cause excessive interfacial reactions at the interface. Sn3.5Ag0.5Cu lead-free solder alloy has been used to identify its interfacial reactions with two-metal layer flexible substrates. In this paper we investigate the dissolution kinetics of Sn3.5Ag0.5Cu solder on electrolytic Ni/electroless NiP layer. It is found that during 1 min of reflow electroless NiP layer dissolves slightly lower than the electrolytic Ni due to the barrier layer formation between the intermetallic compounds (IMCs) and electroless NiP layer. Faster nucleation of IMCs on the electrolytic Ni layer is proposed as the main reason for higher initial dissolution. The appearance of P-rich Ni layer acts as a diffusion barrier layer between the solder and electroless NiP layer, which decreases the dissolution rate and IMCs growth rate than that of the electrolytic Ni layer, but weaken the interface and reduces the ball shear strength and reliability. After acquiring certain thickness P-rich Ni layer breaks and increases the diffusion rate of Sn and as a consequence both the IMCs growth rate and dissolution rate also increases. It is found that 3 lm thick electroless NiP layer cannot protect the Cu layer for more than 120 min at 250°C. In electrolytic Ni shear strength does not change significantly and lower dissolution rate and more protective for Cu layer during long time molten reaction.

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Effect of reaction time on mechanical strength of the interface formed between the Sn-Zn(Bi) solder and the Au/Ni/Cu bond pad

Journal of Electronic Materials, 2006

In this work, the shear strengths and the interfacial reactions of Sn-9Zn, Sn-8Zn-1Bi, and Sn-8Zn... more In this work, the shear strengths and the interfacial reactions of Sn-9Zn, Sn-8Zn-1Bi, and Sn-8Zn-3Bi (wt.%) solders with Au/Ni/Cu ball grid array (BGA) pad metallization were systematically investigated after extended reflows. Zn-containing Pb-free solder alloys were kept in molten condition (240°C) on the Au/electrolytic Ni/Cu bond pads for different time periods ranging from 1 min. to 60 min. to render the ultimate interfacial reaction and to observe the consecutive shear strength. After the shear test, fracture surfaces were investigated by scanning electron microscopy equipped with an energy dispersive x-ray spectrometer. Cross-sectional studies of the interfaces were also conducted to correlate with the fracture surfaces. The solder ball shear load for all the solders during extended reflow increased with the increase of reflow time up to a certain stage and then decreased. It was found that the formation of thick Ni-Zn intermetallic compound (IMC) layers at the solder interface of the Au/electrolytic Ni/Cu bond pad with Sn-Zn(-Bi) alloys deteriorated the mechanical strength of the joints. It was also noticed that the Ni-Zn IMC layer was larger in the Sn-Zn solder system than that in the other two Bi-containing solder systems.

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Interfacial microstructure and shear strength of Ag nano particle doped Sn9Zn solder in ball grid array packages

Microelectronics Reliability, 2009

Sn-9Zn solder joints containing Ag nano particles were prepared by mechanically mixing Ag nano pa... more Sn-9Zn solder joints containing Ag nano particles were prepared by mechanically mixing Ag nano particles (0.3, 0.5 and 1 wt%) with Sn-9Zn solder paste. In the monolithic Sn-Zn solder joints, scallop-shaped AuZn 3 intermetallic compound layers were found at their interfaces. However, after the addition of Ag nano particles, an additional uniform AgZn 3 intermetallic compound layer well adhered to the top surface of the AuZn 3 intermetallic compound layer was found. In addition, in the solder ball region, fine spherical-shaped AgZn 3 intermetallic compound particles were observed as well as Zn-rich and b-Sn phases. With the addition of Ag nano particles, the shear strengths consistently increased with an increase in the Ag nano particle content due to the uniform distribution of fine AgZn 3 intermetallic compound particles. The shear strength of monolithic Sn-Zn and 1 wt% Ag nano particle content Sn-Zn solder joints after one reflow cycle were about 42.1 MPa and 48.9 MPa, respectively, while their shear strengths after eight reflow cycles were about 39.0 MPa and 48.4 MPa, respectively. The AgZn 3 IMCs were found to be uniformly distributed in the b-Sn phase for Ag particle doped Sn-9Zn composite solder joints, which result in an increase in the tensile strength, due to a second phase dispersion strengthening mechanism. The fracture surface of monolithic Sn-Zn solder exhibited a brittle fracture mode with a smooth surface while Sn-Zn solder joints containing Ag nano particles showed a typical ductile failure with very rough dimpled surfaces.

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Dissolution of electroless Ni metallization by lead-free solder alloys

Journal of Alloys and Compounds, 2005

An investigation has been carried out to compare the dissolution of the electroless Ni metallizat... more An investigation has been carried out to compare the dissolution of the electroless Ni metallization of the ball grid array (BGA) substrate into the molten Sn-0.7 wt.%Cu, Sn-3.5 wt.%Ag-0.5 wt.%Cu and Sn-3.5 wt.%Ag solder. A fixed volume of the BGA solder ball (760 m diameter) was used on a 4 m thick electroless Ni(P) metallization over a Cu pad having a circular area with a diameter of 600 m. The dissolution measurement was carried out by measuring the change of Ni(P) metallization thickness as a function of time and temperature. Scanning electron microscopy was used to examine the microstructure of the solder joint and to measure the consumed thickness of Ni(P). The dissolution in Sn-3.5%Ag solder is higher than in the other two lead-free solders. The presence of Cu in the solder plays a major role in inhibiting the consumption of electroless Ni in the soldering reaction. Despite the fact that the initial formation of intermetallic compounds (IMCs) is the highest in Sn-0.7%Cu solder, the formation of the IMCs and the crystallized Ni 3 P is much reduced in the later stage.

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Interfacial reactions of Sn–Cu and Sn–Pb–Ag solder with Au/Ni during extended time reflow in ball grid array packages

Journal of Materials Research, 2004

Lead-free solders with high Sn content cause excessive interfacial reactions at the interface wit... more Lead-free solders with high Sn content cause excessive interfacial reactions at the interface with under-bump metallization during reflow. The interface formed after reflow affects the reliability of the solder joint. For this paper, we investigated the interfacial reactions of Sn0.7Cu and Sn36Pb2Ag solder on electrolytic Ni layer for different reflow times. The traditionally used Sn36Pb2Ag solder was used as a reference. It was found that during as-reflowed, the formation of Cu-rich Sn-Cu-Ni ternary intermetallic compounds (TIMCs) at the interface of Sn0.7Cu solder with electrolytic Ni is much quicker, resulting in the entrapment of some Pb (which is present as impurity in the Sn-Cu solder) rich phase in the TIMCs. During extended time of reflow, high (>30 at.%), medium (30-15 at.%) and low (<15 at.%) Cu TIMCs formed at the interface. The amount of Cu determined the growth rate of TIMCs. Cu-rich TIMCs had higher growth rate and consumed more Ni layer. By contrast, the growth rate of the Ni-Sn binary intermetallic compounds (BIMCs) in the Sn36Pb2Ag solder joint was slower, and the Ni-Sn BIMC was more stable and adherent. The dissolution rate of electrolytic Ni layer for Sn0.7Cu solder joint was higher than the Sn36Pb2Ag solder joints. Less than 3 m of the electrolytic Ni layer was consumed during molten reaction by the higher Sn containing Sn0.7Cu solder in 180 min at 250°C. The shear strength of Sn-Pb-Ag solder joints decreased within 30 min of reflow time from 1.938 to 1.579 kgf due to rapid formation of ternary Ni-Sn-Au compounds on the Ni-Sn BIMCs. The shear strength of Sn0.7Cu solder joint is relatively stable from 1.982 to 1.861 kgf during extended time reflow. Cu prevents the resettlement of Au at the interface. The shear strength does not depend on the thickness of intermetallic compounds (IMCs) and reflow time. Ni/Sn-Cu solder system has higher strength and can be used during prolonged reflow.

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Retardation of spalling by the addition of Ag in Sn–Zn–Bi solder with the Au/Ni metallization

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007

The work presented in this paper focuses on the role of Ag addition in the Sn-8%Zn-3%Bi solder on... more The work presented in this paper focuses on the role of Ag addition in the Sn-8%Zn-3%Bi solder on the shear strengths and the interfacial reactions with Au/Ni/Cu pad metallization in ball grid array (BGA) applications. Sn-Zn-Bi(-Ag) solder alloys were kept in molten condition (240 • C) on the Au/electrolytic Ni/Cu bond pads for different time periods ranging from 1 to 60 min. After the shear test, fracture surfaces were investigated by scanning electron microscopy. Cross-sectional studies of the interfaces were also conducted to correlate with the fracture surfaces. The results indicated that the spalling of the Au-Zn intermetallic compound (IMC) layer was regulated by the addition of 0.3%Ag in Sn-Zn-Bi solder. The retardation of spalling of the initial IMC, limited the formation of Ni-Zn compound in the Ag doped Sn-Zn-Bi solder. The formation of thick Ni-Zn IMC layer in Sn-Zn-Bi alloy deteriorated the mechanical strength of the joints after extended reflow.

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Steady-State Upscaling: From Lamina-Scale to Full-Field Model

SPE Journal, 2000

Summary In recent years, the impact of small-scale permeability structure on hydrocarbon recovery... more

Study on wear properties of aluminium–silicon piston alloy

Journal of Materials Processing Technology, 2001

Low expansion aluminium-silicon eutectic alloys are cast to produce most of the automotive piston... more Low expansion aluminium-silicon eutectic alloys are cast to produce most of the automotive pistons. The structure and properties of these alloys are very much dependent on the cooling rate, composition, modification and heat treatment operations. In this study, locally available automotive 'scrap pistons' were used as basic raw materials and a natural gas fired crucible furnace was used for melting purpose. The wear behaviour of both as-cast and heat treated specimens were studied under dry sliding conditions at room temperature using a pinon-disc type wear testing apparatus. The extent of wear damage and the type of wear were investigated by means of weight loss measurement and optical microscopy techniques. The full heat treatment showed a great influence on the wear properties of the aluminiumsilicon piston alloy as it reduced the wear rate of the specimens. The exceptional high tensile strength and hardness were attributed to the heat treatment condition with decrease in ductility. Significant changes in structure were also observed to occur specially in the primary and eutectic silicon phases. Some of the results of this study can be recommended for tribological use of this alloy in manufacturing automobile spare parts. # 2001 Published by Elsevier Science B.V.

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The role of interfacial interactions and loss function of model adhesives on their adhesion to glass

Journal of Adhesion Science and Technology, 2002

... [13], Xu et al. [14], de Gennes [15], Christensen [16], Greenwood and Johnson [17], and other... more

HRM Final Assignment

The Department of Human Resources Information Systems (HRIS) strives in developing and leading in... more The Department of Human Resources Information Systems (HRIS) strives in developing and leading information system plans that meet Human Resources' automation, data, and information management requirements. In partnership with the University community, the primary focus of HRIS is on establishing innovative solutions to integrated systems, for the administration and deployment of strategic Human Resources information, programs, and services.

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