Jie-Hua Zhao - Academia.edu (original) (raw)
Papers by Jie-Hua Zhao
Physical Review B, 1994
The binding energies E B (D 0 ) and E B (D - ) of neutral and negative donor (D 0 and D - ) cente... more The binding energies E B (D 0 ) and E B (D - ) of neutral and negative donor (D 0 and D - ) centers in quantum dots (QD’s) with different dimensionality and potential shape have been obtained by a variational approach with a trial ...
Annual Review of Materials Science, 2000
▪ As integrated circuit (IC) dimensions continue to decrease, RC delay, crosstalk noise, and po... more ▪ As integrated circuit (IC) dimensions continue to decrease, RC delay, crosstalk noise, and power dissipation of the interconnect structure become limiting factors for ultra-large-scale integration of integrated circuits. Materials with low dielectric constant are being developed to replace silicon dioxide as interlevel dielectrics. In this review, the general requirements for process integration and material properties of low-k dielectrics are first discussed. The discussion is focused on the challenge in developing materials with low dielectric constant but strong thermomechanical properties. This is followed by a description of the material characterization techniques, including several recently developed for porous materials. Finally, the material characteristics of candidate low-k dielectrics will be discussed to illustrate their structure-property relations.
IEEE Transactions on Device and Materials Reliability, 2003
Chip-packaging interaction is becoming a critical reliability issue for Cu/low-chips during assem... more Chip-packaging interaction is becoming a critical reliability issue for Cu/low-chips during assembly into a plastic flip-chip package. With the traditional TEOS interlevel dielectric being replaced by much weaker low-dielectrics, packaging induced interfacial delamination in lowinterconnects has been widely observed, raising serious reliability concerns for Cu/lowchips. In a flip-chip package, the thermal deformation of the package can be directly coupled into the Cu/lowinterconnect structure inducing large local deformation to drive interfacial crack formation. In this paper, we summarize experimental and modeling results from studies performed in our laboratory to investigate the chip-package interaction and its impact on lowinterconnect reliability. We first review the experimental techniques for measuring thermal deformation in a flip-chip package and interfacial fracture energy for lowinterfaces. Then results from three-dimensional finite element analysis (FEA) based on a multilevel submodeling approach in combination with high-resolution moiré interferometry to investigate the chip-package interaction for lowinterconnects are discussed. Packaging induced crack driving forces for relevant interfaces in Cu/lowstructures are deduced and compared with corresponding interfaces in Cu/TEOS and Al/TEOS structures to assess the effect of ILD on packaging reliability. Our results indicate that packaging assembly can significantly impact wafer-level reliability causing interfacial delamination to become a serious reliability concern for Cu/lowstructures.
Applied Physics Letters, 1999
This letter describes measurement of the biaxial modulus, coefficient of thermal expansion (CTE),... more This letter describes measurement of the biaxial modulus, coefficient of thermal expansion (CTE), and moisture uptake characteristics of hydrogen silsesquioxane (HSQ) thin films. The biaxial modulus and CTE were determined using a bending beam method, and moisture ...
Journal of Applied Physics, 1999
Measurement of elastic modulus, Poisson ratio, and coefficient of thermal expansion of on-wafer s... more Measurement of elastic modulus, Poisson ratio, and coefficient of thermal expansion of on-wafer submicron films. [Journal of Applied Physics 85, 6421 (1999)]. Jie-Hua Zhao, Todd Ryan, Paul S. Ho, Andrew J. McKerrow, Wei-Yan Shih. Abstract. ...
AIP Conference Proceedings, 2004
ABSTRACT The package impact to the mechanical integrity of the low dielectric constant (low-k) di... more ABSTRACT The package impact to the mechanical integrity of the low dielectric constant (low-k) dielectrics back end of the line (BEOL) structure has been proven to be significant in recent publications. This work reports a simulation study of the package-induced delamination in low-k structures by interfacial fracture mechanics combined with multi-scale finite element method. The numerical simulation is validated by reliability test results of low-k devices in different flip-chip package configurations. The modeling result is compared to reliability test data of low-k devices in organic, ceramic flip-chip packages, and good correlation is found. Feasibility of flip-chip packaging for low-k devices is demonstrated. The risk of low-k delamination on different package configurations is rated based on both reliability data and numerical simulations.
2011 12th Intl. Conf. on Thermal, Mechanical & Multi-Physics Simulation and Experiments in Microelectronics and Microsystems
Absorption and desorption tests were conducted on five distinct commercial epoxy mold compounds (... more Absorption and desorption tests were conducted on five distinct commercial epoxy mold compounds (EMCs) used in electronic packaging. For absorption, the samples were subjected to 85°C /85% relative humidity and 60°C /85% relative humidity soaking. Desorption conditions were above glass transition temperature at 140°C and 160°C. A dual stage model is developed in this paper for both absorption and desorption
Microelectronics Reliability
ABSTRACT Die cracking in the assembly and reliability testing of flip-chip (FC) packages is often... more ABSTRACT Die cracking in the assembly and reliability testing of flip-chip (FC) packages is often a major concern. A widely used die strength test is the so-called the four-point bending (4PB) test. In the 4PB test, the die is under pure bending and the strength of the die is determined by its breaking tensile stress. Although the 4PB test has been widely used, a well-established relation between the 4PB result and the die breaking in FC package has not been reported. This paper discusses the relation from a probabilistic mechanics point of view. The theory considers the following issues in the material strength test and the application loading conditions: (1) the die top in the 4PB test is under uniaxial tensile stress and the die in FC package is under multi-axial stress; (2) the 4PB test only puts part of the die top under tension and the die top in FC plastic package has almost 100% of the die top area under tension; (3) the die stress in the 4PB and in the package has a different distributions which contribute differently to die cracking. Weibull distribution will be used to analysis the 4PB test data. A three-parameter Weibull distribution fitting procedure will be presented. The function form of the cumulative density function of Weibull distribution is specially modified to take the above three issues into consideration and reflect the stress distribution difference between the test and application. The three-parameter Weibull fitting is compared to a two-parameter fitting. It turns out that some systems need three-parameter fitting and some other systems only need the two-parameter fitting. For systems need three-parameter fitting, a two-parameter fitting will be too conservative in design.
2011 12th Intl. Conf. on Thermal, Mechanical & Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, 2011
ABSTRACT In this paper, a damage mechanics-based continuum theory is developed to provide a theor... more ABSTRACT In this paper, a damage mechanics-based continuum theory is developed to provide a theoretical framework for multi-field problems involving moisture diffusion, heat conduction, moisture evaporation, void growth, and material deformation in a temperature and time-dependent process in encapsulated microelectronics devices. The analysis of moisture diffusion using normalized moisture concentration is re-examined under various conditions, and the applicability of the thermal-moisture analogy is discussed. Effective stress concept is introduced to consider the effect of vapor pressure in the development of a continuum mechanics framework. It turns out that the volumetric strains consist of three parts: thermal expansion (or contraction), hygroscopic swelling, and vapor pressure-induced volumetric strains. Void volume fraction is introduced as a field variable to describe the damage progression. The evolution of void volume fraction is governed by the continuity equation. Vapor pressure is considered as another internal field variable, which is related to moisture evaporation. A complete set of multi-field governing equations are developed. A simplified process, which allows the coupled problem to be solved sequentially, is defined. A bi-material assembly is used to illustrate the multi-field solutions using ANSYS.
AIP Conference Proceedings, 2009
To meet electrical performance requirements, the industry is implementing ultra-low dielectric co... more To meet electrical performance requirements, the industry is implementing ultra-low dielectric constant (ULK) materials in the back end of line interconnect structure. ULK dielectrics are inherently weak compared to traditional dielectrics and pose significant challenges to electronic packaging processes and reliability. Accurate mechanical properties are a pre-requisite for upfront risk assessments associated with low-k integration using numerical simulations. In this paper, techniques used to characterize ULK dielectric elastic modulus and in-plane/out-of-plane coefficient of thermal expansion will be presented and the data for a candidate ULK dielectric will be summarized. Nanoindentation of ULK films on substrate was used to determine the plane strain modulus. In the direction normal to the film, the temperature gradient of the thermal expansion strain along the film thickness was measured by x-ray reflectivity. In the plane of the film, the temperature gradient of the biaxial thermal stress was obtained by the substrate curvature measurements. A method to deduce Poisson's ratio of the thin ULK film is proposed using the data from the afore-mentioned characterization techniques.
Failure induced by die cracking is one of the concerns in flip-chip packaging design and reliabil... more Failure induced by die cracking is one of the concerns in flip-chip packaging design and reliability study. In this paper, a thermal stress model called bi-material plate (BMP) model for analyzing flip-chip packages is developed. The analytical model, which has a closed form solution, is validated by finite element method and extensive experimental measurements for applications in flip-chip packages. Using this model, die stress and curvature can be determined effectively. It offers a significant advantage in estimating the die stress and package reliability in the process of selecting and evaluating the design and material parameters for the flip-chip packages. From this model, it is evident that the curvature and the bending stress are independent of die size if the edge effect is neglected. Further more, the bending stress is independent of absolute die thickness if substrate to die thickness ratio is kept the same. The die curvature and the bending stress have simple correlation...
ITherm 2002. Eighth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (Cat. No.02CH37258), 2002
Solder reliability has been an issue with many fine-pitch, area-array packages because of the lar... more Solder reliability has been an issue with many fine-pitch, area-array packages because of the large thermal expansion (CTE) mismatch between the silicon die and the substrate. One solution to flip-chip plastic ball grid array (FCPBGA) package is to underfill the solder bumps to improve the reliability by reducing the solder bump shear stresses. However, for an underfilled flip-chip package, large
1998 Proceedings. 48th Electronic Components and Technology Conference (Cat. No.98CH36206), 1998
Abstract Plastic flip-chip packaging provides a high-performance and low-cost approach for develo... more Abstract Plastic flip-chip packaging provides a high-performance and low-cost approach for development of electronic packages. The underfill material plays a key role in enhancing shear fatigue reliability of the solder bump interconnection between the chip and the ...
Handbook of Silicon Semiconductor Metrology, 2001
2008 11th Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, 2008
To meet electrical performance requirements, the industry is implementing ultra-low dielectric co... more To meet electrical performance requirements, the industry is implementing ultra-low dielectric constant (ULK) materials in the back end of line interconnect structure. ULK dielectrics are inherently weak compared to traditional dielectrics and pose significant challenges to electronic packaging processes and reliability. Accurate mechanical properties are a prerequisite for upfront risk assessments associated with low-k integration using numerical simulations. In this
2011 IEEE 61st Electronic Components and Technology Conference (ECTC), 2011
Abstract A combined adhesion characterization and fracture mechanics based modeling methodology h... more Abstract A combined adhesion characterization and fracture mechanics based modeling methodology has been developed to predict delamination in lead frame packages. This methodology allows experimental data from a simple adhesion test such as button shear ...
2010 12th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, 2010
ABSTRACT Stress induced parametric shifts caused by packaging are a major source of yield loss in... more ABSTRACT Stress induced parametric shifts caused by packaging are a major source of yield loss in precision devices. Package stress induced parameter shifts can be decomposed into two parts, a mean shifting component and a distribution broadening component. The mean shifting component is systematic and can be compensated in the circuit design phase or by laser-trimming thin film resistors if package stresses are well characterized. However, the distribution broadening component is random in nature due to the random distribution of filler particles against the die surface. This component is hard to handle by design compensation and laser trimming. This work explores the root cause of the random component by a stochastic finite element method (FEM). The epoxy mold compound is modeled as a two-phase composite material consisting of randomly distributed filler particles in an epoxy resin. A predictive methodology that accounts for filler effects and material property mismatch of the fillers and the resin is studied for the first time. The effect of a compliant coating on top of die was simulated by the FEM. The residual stress effect of the compliant coating layer was also accounted for in the simulation. The present work thus incorporates both the systematic and random components of stress in silicon, and suggests yield improvements through package and assembly process optimization. A methodology of generating a conformal FEM mesh of a composite material with a large number of close-packing spheres in a matrix is also presented. This methodology overcomes the difficulty of Boolean operation failures in commercial FEM software packages and provides a feasible way to account for the random distribution of fillers in the mold compound.
2010 12th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, 2010
The ball-on-ring (BOR) test is an effective technique used to characterize the biaxial fracture s... more The ball-on-ring (BOR) test is an effective technique used to characterize the biaxial fracture strength of brittle materials. In particular, damages induced by wafer backgrinding process can be evaluated using the BOR test. It is difficult to measure directly the radius of contact area between the loading ball and a specimen, which is needed for stress determination by an analytic solution. In this study, parametric finite element analyses were performed to compare with known closed-form solutions. It was found that the effect of small loading area must not be ignored and that the radius of contact could be precisely determined using Hertz's contact theory. This can serve as a guideline to accurately obtain the fracture strength of a BOR specimen. KEY WORDS: ball-on-ring (BOR), biaxial strength, Si die fracture, equivalent radius, contact radius, finite element method. NOMENCLATURE E Young's modulus, MPa P load, N R specimen radius, mm a radius of specimen support, mm b radius of uniform loading, mm b eq equivalent radius, mm r radius of loading ball, mm t specimen thickness, mm z radius of contact area between the loading ball and the specimen, mm Greek symbols ν Poisson's ratio σ max maximum tensile stress, MPa
Physical Review B, 1992
A negatively charged donor center D - (ie, a neutral shallow donor D 0 that binds a second electr... more A negatively charged donor center D - (ie, a neutral shallow donor D 0 that binds a second electron) in a spherical quantum dot is studied by use of a variational approach. A trial function which includes electron-correlation effects and approaches the Chandrasekhar-type ...
MRS Proceedings, 1999
In recent years there have been widespread efforts to identify low dielectric constant materials ... more In recent years there have been widespread efforts to identify low dielectric constant materials that can satisfy a number of diverse performance requirements necessary for successful integration into IC devices. This has led to extensive efforts to develop low k materials and the associated process integration. A particularly difficult challenge for material development has been to find the combination of low dielectric constant and good thermal and mechanical stability. In this paper recent characterization results for low k materials performed at the University of Texas will be reviewed, with an emphasis on the relationship of chemical structure to the aforementioned key material properties. For example, measurements showing the effect of film porosity on dielectric constant and thermal and mechanical properties is presented. This data, as well as that for other material types, demonstrates the tradeoffs between dielectric constant and thermomechanical properties that are often m...
Physical Review B, 1994
The binding energies E B (D 0 ) and E B (D - ) of neutral and negative donor (D 0 and D - ) cente... more The binding energies E B (D 0 ) and E B (D - ) of neutral and negative donor (D 0 and D - ) centers in quantum dots (QD’s) with different dimensionality and potential shape have been obtained by a variational approach with a trial ...
Annual Review of Materials Science, 2000
▪ As integrated circuit (IC) dimensions continue to decrease, RC delay, crosstalk noise, and po... more ▪ As integrated circuit (IC) dimensions continue to decrease, RC delay, crosstalk noise, and power dissipation of the interconnect structure become limiting factors for ultra-large-scale integration of integrated circuits. Materials with low dielectric constant are being developed to replace silicon dioxide as interlevel dielectrics. In this review, the general requirements for process integration and material properties of low-k dielectrics are first discussed. The discussion is focused on the challenge in developing materials with low dielectric constant but strong thermomechanical properties. This is followed by a description of the material characterization techniques, including several recently developed for porous materials. Finally, the material characteristics of candidate low-k dielectrics will be discussed to illustrate their structure-property relations.
IEEE Transactions on Device and Materials Reliability, 2003
Chip-packaging interaction is becoming a critical reliability issue for Cu/low-chips during assem... more Chip-packaging interaction is becoming a critical reliability issue for Cu/low-chips during assembly into a plastic flip-chip package. With the traditional TEOS interlevel dielectric being replaced by much weaker low-dielectrics, packaging induced interfacial delamination in lowinterconnects has been widely observed, raising serious reliability concerns for Cu/lowchips. In a flip-chip package, the thermal deformation of the package can be directly coupled into the Cu/lowinterconnect structure inducing large local deformation to drive interfacial crack formation. In this paper, we summarize experimental and modeling results from studies performed in our laboratory to investigate the chip-package interaction and its impact on lowinterconnect reliability. We first review the experimental techniques for measuring thermal deformation in a flip-chip package and interfacial fracture energy for lowinterfaces. Then results from three-dimensional finite element analysis (FEA) based on a multilevel submodeling approach in combination with high-resolution moiré interferometry to investigate the chip-package interaction for lowinterconnects are discussed. Packaging induced crack driving forces for relevant interfaces in Cu/lowstructures are deduced and compared with corresponding interfaces in Cu/TEOS and Al/TEOS structures to assess the effect of ILD on packaging reliability. Our results indicate that packaging assembly can significantly impact wafer-level reliability causing interfacial delamination to become a serious reliability concern for Cu/lowstructures.
Applied Physics Letters, 1999
This letter describes measurement of the biaxial modulus, coefficient of thermal expansion (CTE),... more This letter describes measurement of the biaxial modulus, coefficient of thermal expansion (CTE), and moisture uptake characteristics of hydrogen silsesquioxane (HSQ) thin films. The biaxial modulus and CTE were determined using a bending beam method, and moisture ...
Journal of Applied Physics, 1999
Measurement of elastic modulus, Poisson ratio, and coefficient of thermal expansion of on-wafer s... more Measurement of elastic modulus, Poisson ratio, and coefficient of thermal expansion of on-wafer submicron films. [Journal of Applied Physics 85, 6421 (1999)]. Jie-Hua Zhao, Todd Ryan, Paul S. Ho, Andrew J. McKerrow, Wei-Yan Shih. Abstract. ...
AIP Conference Proceedings, 2004
ABSTRACT The package impact to the mechanical integrity of the low dielectric constant (low-k) di... more ABSTRACT The package impact to the mechanical integrity of the low dielectric constant (low-k) dielectrics back end of the line (BEOL) structure has been proven to be significant in recent publications. This work reports a simulation study of the package-induced delamination in low-k structures by interfacial fracture mechanics combined with multi-scale finite element method. The numerical simulation is validated by reliability test results of low-k devices in different flip-chip package configurations. The modeling result is compared to reliability test data of low-k devices in organic, ceramic flip-chip packages, and good correlation is found. Feasibility of flip-chip packaging for low-k devices is demonstrated. The risk of low-k delamination on different package configurations is rated based on both reliability data and numerical simulations.
2011 12th Intl. Conf. on Thermal, Mechanical & Multi-Physics Simulation and Experiments in Microelectronics and Microsystems
Absorption and desorption tests were conducted on five distinct commercial epoxy mold compounds (... more Absorption and desorption tests were conducted on five distinct commercial epoxy mold compounds (EMCs) used in electronic packaging. For absorption, the samples were subjected to 85°C /85% relative humidity and 60°C /85% relative humidity soaking. Desorption conditions were above glass transition temperature at 140°C and 160°C. A dual stage model is developed in this paper for both absorption and desorption
Microelectronics Reliability
ABSTRACT Die cracking in the assembly and reliability testing of flip-chip (FC) packages is often... more ABSTRACT Die cracking in the assembly and reliability testing of flip-chip (FC) packages is often a major concern. A widely used die strength test is the so-called the four-point bending (4PB) test. In the 4PB test, the die is under pure bending and the strength of the die is determined by its breaking tensile stress. Although the 4PB test has been widely used, a well-established relation between the 4PB result and the die breaking in FC package has not been reported. This paper discusses the relation from a probabilistic mechanics point of view. The theory considers the following issues in the material strength test and the application loading conditions: (1) the die top in the 4PB test is under uniaxial tensile stress and the die in FC package is under multi-axial stress; (2) the 4PB test only puts part of the die top under tension and the die top in FC plastic package has almost 100% of the die top area under tension; (3) the die stress in the 4PB and in the package has a different distributions which contribute differently to die cracking. Weibull distribution will be used to analysis the 4PB test data. A three-parameter Weibull distribution fitting procedure will be presented. The function form of the cumulative density function of Weibull distribution is specially modified to take the above three issues into consideration and reflect the stress distribution difference between the test and application. The three-parameter Weibull fitting is compared to a two-parameter fitting. It turns out that some systems need three-parameter fitting and some other systems only need the two-parameter fitting. For systems need three-parameter fitting, a two-parameter fitting will be too conservative in design.
2011 12th Intl. Conf. on Thermal, Mechanical & Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, 2011
ABSTRACT In this paper, a damage mechanics-based continuum theory is developed to provide a theor... more ABSTRACT In this paper, a damage mechanics-based continuum theory is developed to provide a theoretical framework for multi-field problems involving moisture diffusion, heat conduction, moisture evaporation, void growth, and material deformation in a temperature and time-dependent process in encapsulated microelectronics devices. The analysis of moisture diffusion using normalized moisture concentration is re-examined under various conditions, and the applicability of the thermal-moisture analogy is discussed. Effective stress concept is introduced to consider the effect of vapor pressure in the development of a continuum mechanics framework. It turns out that the volumetric strains consist of three parts: thermal expansion (or contraction), hygroscopic swelling, and vapor pressure-induced volumetric strains. Void volume fraction is introduced as a field variable to describe the damage progression. The evolution of void volume fraction is governed by the continuity equation. Vapor pressure is considered as another internal field variable, which is related to moisture evaporation. A complete set of multi-field governing equations are developed. A simplified process, which allows the coupled problem to be solved sequentially, is defined. A bi-material assembly is used to illustrate the multi-field solutions using ANSYS.
AIP Conference Proceedings, 2009
To meet electrical performance requirements, the industry is implementing ultra-low dielectric co... more To meet electrical performance requirements, the industry is implementing ultra-low dielectric constant (ULK) materials in the back end of line interconnect structure. ULK dielectrics are inherently weak compared to traditional dielectrics and pose significant challenges to electronic packaging processes and reliability. Accurate mechanical properties are a pre-requisite for upfront risk assessments associated with low-k integration using numerical simulations. In this paper, techniques used to characterize ULK dielectric elastic modulus and in-plane/out-of-plane coefficient of thermal expansion will be presented and the data for a candidate ULK dielectric will be summarized. Nanoindentation of ULK films on substrate was used to determine the plane strain modulus. In the direction normal to the film, the temperature gradient of the thermal expansion strain along the film thickness was measured by x-ray reflectivity. In the plane of the film, the temperature gradient of the biaxial thermal stress was obtained by the substrate curvature measurements. A method to deduce Poisson's ratio of the thin ULK film is proposed using the data from the afore-mentioned characterization techniques.
Failure induced by die cracking is one of the concerns in flip-chip packaging design and reliabil... more Failure induced by die cracking is one of the concerns in flip-chip packaging design and reliability study. In this paper, a thermal stress model called bi-material plate (BMP) model for analyzing flip-chip packages is developed. The analytical model, which has a closed form solution, is validated by finite element method and extensive experimental measurements for applications in flip-chip packages. Using this model, die stress and curvature can be determined effectively. It offers a significant advantage in estimating the die stress and package reliability in the process of selecting and evaluating the design and material parameters for the flip-chip packages. From this model, it is evident that the curvature and the bending stress are independent of die size if the edge effect is neglected. Further more, the bending stress is independent of absolute die thickness if substrate to die thickness ratio is kept the same. The die curvature and the bending stress have simple correlation...
ITherm 2002. Eighth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (Cat. No.02CH37258), 2002
Solder reliability has been an issue with many fine-pitch, area-array packages because of the lar... more Solder reliability has been an issue with many fine-pitch, area-array packages because of the large thermal expansion (CTE) mismatch between the silicon die and the substrate. One solution to flip-chip plastic ball grid array (FCPBGA) package is to underfill the solder bumps to improve the reliability by reducing the solder bump shear stresses. However, for an underfilled flip-chip package, large
1998 Proceedings. 48th Electronic Components and Technology Conference (Cat. No.98CH36206), 1998
Abstract Plastic flip-chip packaging provides a high-performance and low-cost approach for develo... more Abstract Plastic flip-chip packaging provides a high-performance and low-cost approach for development of electronic packages. The underfill material plays a key role in enhancing shear fatigue reliability of the solder bump interconnection between the chip and the ...
Handbook of Silicon Semiconductor Metrology, 2001
2008 11th Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, 2008
To meet electrical performance requirements, the industry is implementing ultra-low dielectric co... more To meet electrical performance requirements, the industry is implementing ultra-low dielectric constant (ULK) materials in the back end of line interconnect structure. ULK dielectrics are inherently weak compared to traditional dielectrics and pose significant challenges to electronic packaging processes and reliability. Accurate mechanical properties are a prerequisite for upfront risk assessments associated with low-k integration using numerical simulations. In this
2011 IEEE 61st Electronic Components and Technology Conference (ECTC), 2011
Abstract A combined adhesion characterization and fracture mechanics based modeling methodology h... more Abstract A combined adhesion characterization and fracture mechanics based modeling methodology has been developed to predict delamination in lead frame packages. This methodology allows experimental data from a simple adhesion test such as button shear ...
2010 12th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, 2010
ABSTRACT Stress induced parametric shifts caused by packaging are a major source of yield loss in... more ABSTRACT Stress induced parametric shifts caused by packaging are a major source of yield loss in precision devices. Package stress induced parameter shifts can be decomposed into two parts, a mean shifting component and a distribution broadening component. The mean shifting component is systematic and can be compensated in the circuit design phase or by laser-trimming thin film resistors if package stresses are well characterized. However, the distribution broadening component is random in nature due to the random distribution of filler particles against the die surface. This component is hard to handle by design compensation and laser trimming. This work explores the root cause of the random component by a stochastic finite element method (FEM). The epoxy mold compound is modeled as a two-phase composite material consisting of randomly distributed filler particles in an epoxy resin. A predictive methodology that accounts for filler effects and material property mismatch of the fillers and the resin is studied for the first time. The effect of a compliant coating on top of die was simulated by the FEM. The residual stress effect of the compliant coating layer was also accounted for in the simulation. The present work thus incorporates both the systematic and random components of stress in silicon, and suggests yield improvements through package and assembly process optimization. A methodology of generating a conformal FEM mesh of a composite material with a large number of close-packing spheres in a matrix is also presented. This methodology overcomes the difficulty of Boolean operation failures in commercial FEM software packages and provides a feasible way to account for the random distribution of fillers in the mold compound.
2010 12th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, 2010
The ball-on-ring (BOR) test is an effective technique used to characterize the biaxial fracture s... more The ball-on-ring (BOR) test is an effective technique used to characterize the biaxial fracture strength of brittle materials. In particular, damages induced by wafer backgrinding process can be evaluated using the BOR test. It is difficult to measure directly the radius of contact area between the loading ball and a specimen, which is needed for stress determination by an analytic solution. In this study, parametric finite element analyses were performed to compare with known closed-form solutions. It was found that the effect of small loading area must not be ignored and that the radius of contact could be precisely determined using Hertz's contact theory. This can serve as a guideline to accurately obtain the fracture strength of a BOR specimen. KEY WORDS: ball-on-ring (BOR), biaxial strength, Si die fracture, equivalent radius, contact radius, finite element method. NOMENCLATURE E Young's modulus, MPa P load, N R specimen radius, mm a radius of specimen support, mm b radius of uniform loading, mm b eq equivalent radius, mm r radius of loading ball, mm t specimen thickness, mm z radius of contact area between the loading ball and the specimen, mm Greek symbols ν Poisson's ratio σ max maximum tensile stress, MPa
Physical Review B, 1992
A negatively charged donor center D - (ie, a neutral shallow donor D 0 that binds a second electr... more A negatively charged donor center D - (ie, a neutral shallow donor D 0 that binds a second electron) in a spherical quantum dot is studied by use of a variational approach. A trial function which includes electron-correlation effects and approaches the Chandrasekhar-type ...
MRS Proceedings, 1999
In recent years there have been widespread efforts to identify low dielectric constant materials ... more In recent years there have been widespread efforts to identify low dielectric constant materials that can satisfy a number of diverse performance requirements necessary for successful integration into IC devices. This has led to extensive efforts to develop low k materials and the associated process integration. A particularly difficult challenge for material development has been to find the combination of low dielectric constant and good thermal and mechanical stability. In this paper recent characterization results for low k materials performed at the University of Texas will be reviewed, with an emphasis on the relationship of chemical structure to the aforementioned key material properties. For example, measurements showing the effect of film porosity on dielectric constant and thermal and mechanical properties is presented. This data, as well as that for other material types, demonstrates the tradeoffs between dielectric constant and thermomechanical properties that are often m...