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Dive into the research topics where R. Mahajan is active.

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Featured researches published by R. Mahajan.


Journal of Electronic Materials | 2012

Fracture of Sn-Ag-Cu Solder Joints on Cu Substrates:I. Effects of Loading and Processing Conditions

Z. Huang; Praveen Kumar; I. Dutta; John Hock Lye Pang; Rajen S. Sidhu; M. Renavikar; R. Mahajan

During service, microcracks form inside solder joints, making microelectronic packages highly prone to failure on dropping. Hence, the fracture behavior of solder joints under drop conditions at high strain rates and under mixed-mode conditions is a critically important design consideration for robust joints. This study reports on the effects of joint processing and loading conditions on the microstructure and fracture response of Sn-3.8%Ag-0.7%Cu (SAC387) solder joints attached to Cu substrates. The impact of parameters which control the microstructure (reflow condition, aging) as well as loading conditions (strain rate and loading angle) are explicitly studied. A methodology based on the calculation of the critical energy release rate, GC, using compact mixed-mode (CMM) samples was developed to quantify the fracture toughness of the joints under conditions of adhesive (i.e., interface-related) fracture. In general, higher strain rate and increased mode-mixity resulted in decreased GC. GC also decreased with increasing dwell time at reflow temperature, which produced a thicker intermetallic layer at the solder–substrate interface. Softer solders, produced by slower cooling following reflow, or post-reflow aging, showed enhanced GC. The sensitivity of the fracture toughness to all of the aforementioned parameters reduced with an increase in the mode-mixity. Fracture mechanisms, elucidating the effects of the loading conditions and process parameters, are briefly highlighted.


ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, MEMS and NEMS: Volume 2 | 2011

Effect of Interfacial Layers on the Performance of Cu-In Liquid Phase Sintered Composites as Thermal Interface and Interconnect Materials

J. Liu; Praveen Kumar; I. Dutta; C. M. Nagaraj; Rishi Raj; M. Renavikar; R. Mahajan

In this study, a novel architecture composed of uniformly distributed high melting phase (HMP, e.g. Cu) in a low melting phase (LMP, e.g. In) matrix, which can be produced via liquid phase sintering (LPS), is proposed to produce next generation thermal interface materials (TIMs) and interconnect (IC) materials. The LMP determines the shear compliance of these composites whereas the HMP determines its thermal and electrical conductivities. The volume fraction of In was optimized to produce a Cu-In solder with suitable mechanical, electrical and thermal properties for TIM and IC applications. Since, Cu and In react to form several Cu-In intermetallic compounds (IMCs), which may deteriorate the long-term performance of these solders, interfacial-layers of Au and Al2 O3 were applied on Cu to further improve the performance of the Cu-In solders. The effect of interfacial-layers on the reaction between Cu and In, during sintering at 160°C and during aging at 125°C, was studied and its impact on the mechanical, thermal and electrical properties was evaluated. Au interfacial layer (50∼200nm) quickly reacted with In to form AuIn2 IMC, which acted as a tenacious diffusion-barrier and slowed down the reactions between Cu and In. 8-monolayer thick Al2 O3 did not react with either Cu or In and inhibited reactions between Cu and In. During short-time sintering, the effect of interfacial layer on the thicknesses of IMCs was insignificant to affect the yield strength of the as-sintered composites. However, IMC layer thickened rapidly in the Cu-In composites without an interfacial-layer, which led to a drastic decrease in the volume fraction of unreacted In leading to an increase in the yield strength of the solder. On the other hand, the interfacial-layers effectively suppressed the growth of IMCs during aging and hence the yield strength of such composites increased at slower rates. Since, the IMCs formed at the interface radically affect the contact resistance, significant differences in the thermal and electrical conductivities were recorded for the solders with different interfacial-layers.Copyright


ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, MEMS and NEMS: Volume 2 | 2011

High Strain Rate Fracture Behavior of Sn-Ag-Cu Solder Joints on Cu Substrates

Z. Huang; Praveen Kumar; I. Dutta; John H. L. Pang; Rajen S. Sidhu; M. Renavikar; R. Mahajan

During service, micro-cracks form inside solder joints, making a microelectronic package prone to failure particularly during a drop. Hence, the understanding of the fracture behavior of solder joints under drop conditions, synonymously at high strain rates and in mixed mode, is critically important. This study reports: (i) the effects of processing conditions (reflow parameters and aging) on the microstructure and fracture behavior of Sn-3.8%Ag-0.7%Cu (SAC387) solder joints attached to Cu substrates, and (ii) the effects of the loading conditions (strain rate and loading angle) on the fracture toughness of these joints, especially at high strain rates. A methodology for calculating critical energy release rate, GC , was employed to quantify the fracture toughness of the joints. Two parameters, (i) effective thickness of the interfacial intermetallic compounds (IMC) layer, which is proportional to the product of the thickness and the roughness of the IMC layer, and (ii) yield strength of the solder, which depends on the solder microstructure and the loading rate, were identified as the dominant quantities affecting the fracture behavior of the solder joints. The fracture toughness of the solder joint decreased with an increase in the effective thickness of the IMC layer and the yield strength of the solder. A 2-dimensional fracture mechanism map with the effective thickness of the IMC layer and the yield strength of the solder as two axes and the fracture toughness as well as the fraction of different fracture paths as contour-lines was prepared. Trends in the fracture toughness of the solder joints and their correlation with the fracture modes are explained using the fracture mechanism map.Copyright


electronics packaging technology conference | 2010

Fracture mechanism map for the fracture of microelectronic Pb-free solder joints under dynamic loading conditions

Z. Huang; Praveen Kumar; I. Dutta; John H. L. Pang; Rajen S. Sidhu; M. Renavikar; R. Mahajan

Solder joints, which serve as mechanical and electrical interconnects in a package, are particularly prone to failure during a drop. Hence, the fracture behavior of solders at high strain rates and in mixed mode is a critically important design parameter. This study reports the effects of (a) loading conditions (strain rate and loading angle), (b) reflow parameters (dwell time and cooling rate), and (c) post-reflow aging on the mixed mode fracture toughness of a lead-free solder (Sn-3.8%Ag-0.7%Cu)/Cu joint. A methodology based on the calculation of critical energy release rate, GC, which is equal to the fracture toughness of a material under limited plasticity condition, was employed. An increase in the strain rate results in limited plasticity ahead of the crack tip leading to a reduction in the fracture toughness of the solder joints. Fracture toughness also decreases with increasing mode-mixity (up to a loading angle of 75°). A slower cooling rate increases the fracture toughness whereas a longer dwell time adversely affects it. Also, aged samples show higher GC value. A fracture mechanism map is developed to describe the correlation between the yield strength of the solder, which depends on the solder microstructure and the loading rate, the IMC morphology, which depends on the reflow conditions and aging, and the fracture toughness of the solder joint.


ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems collocated with the ASME 2005 Heat Transfer Summer Conference | 2005

Creep Behavior of Lead Free Solder Interconnects in Microelectronic Packages: Impression Creep Testing and Constitutive Modeling

I. Dutta; D. Pan; S.G. Jadhav; R. Mahajan

The creep behavior of ball grid array (BGA) or flip-chip (FC) solder joints during thermo-mechanical cycling associated with service often limits the reliability of microelectronic packages. In addition, the fine intermetallic precipitates (Ag3 Sn and/or Cu6 Sn5 ) in the microstructures of the new lead-free solders (Sn-Ag and Sn-Ag-Cu) can undergo significant in situ strain-enhanced coarsening during TMC, resulting in in-service evolution of the creep behavior of the joints. Since there are significant microstructural/ compositional differences between bulk solder samples and tiny microelectronic solder joints, it is critical to develop accurate creep testing methodologies on tiny life-sized solder joints and microstructurally adaptive constitutive creep models for the emerging Pb-free solder alloys. In this paper, we present creep data obtained from tests conducted on individual Sn4Ag0.5Cu ball grid array (BGA) solder balls attached to a packaging substrate, using a newly developed miniaturized impression creep apparatus, which affords high test throughput with minimal sample preparation. Coarsening of intermetallic particles is demonstrated to influence creep behavior in two ways. At low stresses, the creep rate increases proportionately with precipitate size. At high stresses, precipitate coarsening influences creep response by altering the threshold stress for particle-limited creep. Based on the experimental observations, a microstructurally adaptive creep model, which accounts for the effects of coarsening on the creep response of solder joints, and is capable of adjusting itself as solder joint microstructures evolve during service, is presented, along with experimental determination of the relevant coarsening kinetics parameters.Copyright


Journal of Materials Science | 2007

A comparison of impression and compression creep behavior of polycrystalline Sn

C. Park; X. Long; S. Haberman; S. Ma; I. Dutta; R. Mahajan; S. G. Jadhav


Journal of Electronic Materials | 2012

Fracture of Sn-Ag-Cu Solder Joints on Cu Substrates. II: Fracture Mechanism Map

Praveen Kumar; Z. Huang; I. Dutta; Rajen S. Sidhu; M. Renavikar; R. Mahajan


Journal of Materials Science | 2011

Liquid phase sintered Cu–In composite solders for thermal interface material and interconnect applications

J. Liu; Praveen Kumar; I. Dutta; Rishi Raj; R. Sidhu; M. Renavikar; R. Mahajan


Journal of Materials Science | 2014

Interfacially engineered liquid-phase-sintered Cu–In composite solders for thermal interface material applications

J. Liu; Uttara Sahaym; I. Dutta; Rishi Raj; M. Renavikar; Rajen S. Sidhu; R. Mahajan


Journal of Electronic Materials | 2014

Incorporation of Interfacial Intermetallic Morphology in Fracture Mechanism Map for Sn-Ag-Cu Solder Joints

Z. Huang; Praveen Kumar; I. Dutta; Rajen S. Sidhu; M. Renavikar; R. Mahajan

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I. Dutta

Washington State University

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Praveen Kumar

Indian Institute of Science

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Z. Huang

Washington State University

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J. Liu

Washington State University

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Rishi Raj

University of Colorado Boulder

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John H. L. Pang

Nanyang Technological University

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C. M. Nagaraj

University of Colorado Boulder

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C. Park

Naval Postgraduate School

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