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Papers by Gerald Pham-van-diep
26th Aerospace Sciences Meeting, 1988
Thermoplastics have started to gain acceptance in some of the more challenging areas of advanced ... more Thermoplastics have started to gain acceptance in some of the more challenging areas of advanced packaging, including MEMS, where lower cost, cavity style packages are required. Thermoplastics, like LCP, PPS and PEEK, can withstand exposure to over 300oC thus assuring lead-free solder capability. Many polymers offer superior moisture resistance, can be formed into micro-precision packages in just seconds, and are easily recycled. Epoxies, the non-hermetic package standard for more than 50 years, can’t be remelted for reuse, have unremarkable moisture properties, and typically contain elements, like bromine, that put them on the environmental target list. Some halogen compounds have already been banned. Fortunately, several modern high-performance halogen-free thermoplastics are inherently flame retardant and these nontoxic materials have an excellent record of use in telecommunications, medical, and automotive fields. This paper will describe advances in thermoplastic packaging prod...
A technique that enhances the release of solder paste from stencils during the print process has ... more A technique that enhances the release of solder paste from stencils during the print process has been developed. The technique is based on applying variable high frequency and low amplitude vibrations to the stencil during the stencil/substrate separation sequence. The effects of the technique are demonstrated in the context of bumping wafers. It is shown that the enhanced print technique produces wafers with less defects, greater bump heights and better height uniformity than when conventional stencil printing is used without the enhancement technique.
The objectives of this study are to determine the point at which the stencil printing process bec... more The objectives of this study are to determine the point at which the stencil printing process becomes inefficient and to compare the difference in performance between aperture geometry (thickness, shape and taper) for typical aperture sizes ranging from 6 to 20 mils. Two laser cut stencil thicknesses (4 and 5 mils) and three levels of positive taper, low (3°), medium (5°) and high (7°) are investigated.
Velocity distribution functions in normal shock waves in argon and helium are calculated using Mo... more Velocity distribution functions in normal shock waves in argon and helium are calculated using Monte Carlo direct simulation. These are compared with experimental results for argon at M = 7.18 and for helium at M = 1.59 and 20. For both argon and helium, the variable-hard-sphere (VHS) model is used for the elastic scattering cross section, with the velocity dependence derived from a viscosity-temperature power-law relationship in the way normally used by Bird (1976).
Apparatus for performing operations on at least one surface of an electronic substrate having a f... more Apparatus for performing operations on at least one surface of an electronic substrate having a first surface and a second surface, said apparatus comprising: a frame; a transport system that moves the substrate through the apparatus; a frame coupled with the substrate support system comprising a non-rigid portion that contacts the substrate during an operation on the substrate and is supported, wherein the non-rigid portion flexure of the substrate before and during allows performing an operation on the substrate; and a coupled to the frame device that performs an operation on a surface of the substrate.
The sealed hermetic package is over 100 years old if we include cathode ray and vacuum tubes. Whi... more The sealed hermetic package is over 100 years old if we include cathode ray and vacuum tubes. While the package has changed, the idea of making a near-perfect gas-tight enclosure has remained constant. The metal and ceramic full hermetic package may be required for applications that cannot use the non-hermetic plastic package, but is there an intermediate package choice? During the last few years, the electronic packaging industry has sought to develop the Near-Hermetic Package (NHP), a design that is “good enough” and “cheap enough” to satisfy some special devices like MEMS. This paper will describe work with Liquid Crystal Polymer (LCP) injection-molded enclosures that are targeting MEMS and some optical device applications. The work involves sealing lids and chip carriers with laser energy. The package design creates a cavity type enclosure that can provide the “free space” necessary for mechanical motion found in some MEMS devices. We will also briefly describe getters (contamin...
25th Joint Propulsion Conference, 1989
A method for measuring the axial and transverse plume velocities and internal energy distribution... more A method for measuring the axial and transverse plume velocities and internal energy distributions in rarified thruster plumes by using pulsed laser-induced fluorescence (LIF) of atomic hydrogen Balmer lines is described. The results of an application of this technique for velocity mapping of a 30-kW ammonia arc-jet plume generated in the JPL arc-jet testing facility (which is uniquely suited for
Physics of Fluids A: Fluid Dynamics, 1991
One‐dimensional shock wave properties in helium and argon are predicted using Monte Carlo direct ... more One‐dimensional shock wave properties in helium and argon are predicted using Monte Carlo direct simulation. The collision model is based directly on the interatomic potential, taking angular scattering into account. The potential is assumed to be of the MaitlandSmith [n(r)−6] ...
30th Aerospace Sciences Meeting and Exhibit, 1992
28th Joint Propulsion Conference and Exhibit, 1992
ABSTRACT
Several aspects of the kinetic models used in the collision phase of Monte Carlo direct simulatio... more Several aspects of the kinetic models used in the collision phase of Monte Carlo direct simulations have been studied. Accurate molecular velocity distribution function predictions require a significantly increased number of computational cells in one maximum slope shock thickness, compared to predictions of macroscopic properties. The shape of the highly repulsive portion of the interatomic potential for argon is not well modeled by conventional interatomic potentials; this portion of the potential controls high Mach number shock thickness predictions, indicating that the specification of the energetic repulsive portion of interatomic or intermolecular potentials must be chosen with care for correct modeling of nonequilibrium flows at high temperatures. It has been shown for inverse power potentials that the assumption of variable hard sphere scattering provides accurate predictions of the macroscopic properties in shock waves, by comparison with simulations in which differential s...
Science, 1989
13. The trailing side of Io experiences a higher flux of low energy electrons and ions than the l... more 13. The trailing side of Io experiences a higher flux of low energy electrons and ions than the leading side; .however, it is the more energetic particles that are relevant to surface discharges.
Journal of Fluid Mechanics, 1991
Numerical experiments have been performed on normal shock waves with Monte Carlo Direct Simulatio... more Numerical experiments have been performed on normal shock waves with Monte Carlo Direct Simulations (MCDS's) to investigate the validity of continuum theories a t very low Mach numbers. Results from the NavierStokes and the Burnett equations are compared to MCDS's for both hard-sphere and Maxwell gases. It is found that the maximum-slope shock thicknesses are described equally well (within the MCDS computational scatter) by either of the continuum formulations for Mach numbers smaller than about 1.2. For Mach numbers greater than 1.2, the Burnett predictions are more accurate than the NavierStokes results. Temperature-density profile separations are best described by the Burnett equations for Mach numbers greater than about 1.3. At lower Mach numbers the MCDS scatter is too great to differentiate between the two continuum theories. For all Mach numbers above one, the shock shapes are more accurately described by the Burnett equations.
JOURNAL …, 2003
Three studies are undertaken to understand the dependence of aperture fill and stencil release on... more Three studies are undertaken to understand the dependence of aperture fill and stencil release on solder paste print definition. The first study focuses on the role of pastes. Seven pastes are compared and ranked by release performance. Second, three stencil-...
Abstract A technique that enhances the release of solder paste from stencils during the print pro... more Abstract A technique that enhances the release of solder paste from stencils during the print process has been developed. The technique is based on applying variable high frequency and low amplitude vibrations to the stencil during the stencil/substrate separation ...
AIAA Journal, 1991
ABSTRACT
The development of a university scale source for intense beams of energetic, neutral atmospheric ... more The development of a university scale source for intense beams of energetic, neutral atmospheric species is discussed. An unconventional plasma source is used to produce a beam of ions that can be mass selected, focused, and slowed to appropriate energies. Subsequently, neutralization of the energetic ion stream is achieved by charge exchange collisions between the ion beam and molecules of
26th Aerospace Sciences Meeting, 1988
Thermoplastics have started to gain acceptance in some of the more challenging areas of advanced ... more Thermoplastics have started to gain acceptance in some of the more challenging areas of advanced packaging, including MEMS, where lower cost, cavity style packages are required. Thermoplastics, like LCP, PPS and PEEK, can withstand exposure to over 300oC thus assuring lead-free solder capability. Many polymers offer superior moisture resistance, can be formed into micro-precision packages in just seconds, and are easily recycled. Epoxies, the non-hermetic package standard for more than 50 years, can’t be remelted for reuse, have unremarkable moisture properties, and typically contain elements, like bromine, that put them on the environmental target list. Some halogen compounds have already been banned. Fortunately, several modern high-performance halogen-free thermoplastics are inherently flame retardant and these nontoxic materials have an excellent record of use in telecommunications, medical, and automotive fields. This paper will describe advances in thermoplastic packaging prod...
A technique that enhances the release of solder paste from stencils during the print process has ... more A technique that enhances the release of solder paste from stencils during the print process has been developed. The technique is based on applying variable high frequency and low amplitude vibrations to the stencil during the stencil/substrate separation sequence. The effects of the technique are demonstrated in the context of bumping wafers. It is shown that the enhanced print technique produces wafers with less defects, greater bump heights and better height uniformity than when conventional stencil printing is used without the enhancement technique.
The objectives of this study are to determine the point at which the stencil printing process bec... more The objectives of this study are to determine the point at which the stencil printing process becomes inefficient and to compare the difference in performance between aperture geometry (thickness, shape and taper) for typical aperture sizes ranging from 6 to 20 mils. Two laser cut stencil thicknesses (4 and 5 mils) and three levels of positive taper, low (3°), medium (5°) and high (7°) are investigated.
Velocity distribution functions in normal shock waves in argon and helium are calculated using Mo... more Velocity distribution functions in normal shock waves in argon and helium are calculated using Monte Carlo direct simulation. These are compared with experimental results for argon at M = 7.18 and for helium at M = 1.59 and 20. For both argon and helium, the variable-hard-sphere (VHS) model is used for the elastic scattering cross section, with the velocity dependence derived from a viscosity-temperature power-law relationship in the way normally used by Bird (1976).
Apparatus for performing operations on at least one surface of an electronic substrate having a f... more Apparatus for performing operations on at least one surface of an electronic substrate having a first surface and a second surface, said apparatus comprising: a frame; a transport system that moves the substrate through the apparatus; a frame coupled with the substrate support system comprising a non-rigid portion that contacts the substrate during an operation on the substrate and is supported, wherein the non-rigid portion flexure of the substrate before and during allows performing an operation on the substrate; and a coupled to the frame device that performs an operation on a surface of the substrate.
The sealed hermetic package is over 100 years old if we include cathode ray and vacuum tubes. Whi... more The sealed hermetic package is over 100 years old if we include cathode ray and vacuum tubes. While the package has changed, the idea of making a near-perfect gas-tight enclosure has remained constant. The metal and ceramic full hermetic package may be required for applications that cannot use the non-hermetic plastic package, but is there an intermediate package choice? During the last few years, the electronic packaging industry has sought to develop the Near-Hermetic Package (NHP), a design that is “good enough” and “cheap enough” to satisfy some special devices like MEMS. This paper will describe work with Liquid Crystal Polymer (LCP) injection-molded enclosures that are targeting MEMS and some optical device applications. The work involves sealing lids and chip carriers with laser energy. The package design creates a cavity type enclosure that can provide the “free space” necessary for mechanical motion found in some MEMS devices. We will also briefly describe getters (contamin...
25th Joint Propulsion Conference, 1989
A method for measuring the axial and transverse plume velocities and internal energy distribution... more A method for measuring the axial and transverse plume velocities and internal energy distributions in rarified thruster plumes by using pulsed laser-induced fluorescence (LIF) of atomic hydrogen Balmer lines is described. The results of an application of this technique for velocity mapping of a 30-kW ammonia arc-jet plume generated in the JPL arc-jet testing facility (which is uniquely suited for
Physics of Fluids A: Fluid Dynamics, 1991
One‐dimensional shock wave properties in helium and argon are predicted using Monte Carlo direct ... more One‐dimensional shock wave properties in helium and argon are predicted using Monte Carlo direct simulation. The collision model is based directly on the interatomic potential, taking angular scattering into account. The potential is assumed to be of the MaitlandSmith [n(r)−6] ...
30th Aerospace Sciences Meeting and Exhibit, 1992
28th Joint Propulsion Conference and Exhibit, 1992
ABSTRACT
Several aspects of the kinetic models used in the collision phase of Monte Carlo direct simulatio... more Several aspects of the kinetic models used in the collision phase of Monte Carlo direct simulations have been studied. Accurate molecular velocity distribution function predictions require a significantly increased number of computational cells in one maximum slope shock thickness, compared to predictions of macroscopic properties. The shape of the highly repulsive portion of the interatomic potential for argon is not well modeled by conventional interatomic potentials; this portion of the potential controls high Mach number shock thickness predictions, indicating that the specification of the energetic repulsive portion of interatomic or intermolecular potentials must be chosen with care for correct modeling of nonequilibrium flows at high temperatures. It has been shown for inverse power potentials that the assumption of variable hard sphere scattering provides accurate predictions of the macroscopic properties in shock waves, by comparison with simulations in which differential s...
Science, 1989
13. The trailing side of Io experiences a higher flux of low energy electrons and ions than the l... more 13. The trailing side of Io experiences a higher flux of low energy electrons and ions than the leading side; .however, it is the more energetic particles that are relevant to surface discharges.
Journal of Fluid Mechanics, 1991
Numerical experiments have been performed on normal shock waves with Monte Carlo Direct Simulatio... more Numerical experiments have been performed on normal shock waves with Monte Carlo Direct Simulations (MCDS's) to investigate the validity of continuum theories a t very low Mach numbers. Results from the NavierStokes and the Burnett equations are compared to MCDS's for both hard-sphere and Maxwell gases. It is found that the maximum-slope shock thicknesses are described equally well (within the MCDS computational scatter) by either of the continuum formulations for Mach numbers smaller than about 1.2. For Mach numbers greater than 1.2, the Burnett predictions are more accurate than the NavierStokes results. Temperature-density profile separations are best described by the Burnett equations for Mach numbers greater than about 1.3. At lower Mach numbers the MCDS scatter is too great to differentiate between the two continuum theories. For all Mach numbers above one, the shock shapes are more accurately described by the Burnett equations.
JOURNAL …, 2003
Three studies are undertaken to understand the dependence of aperture fill and stencil release on... more Three studies are undertaken to understand the dependence of aperture fill and stencil release on solder paste print definition. The first study focuses on the role of pastes. Seven pastes are compared and ranked by release performance. Second, three stencil-...
Abstract A technique that enhances the release of solder paste from stencils during the print pro... more Abstract A technique that enhances the release of solder paste from stencils during the print process has been developed. The technique is based on applying variable high frequency and low amplitude vibrations to the stencil during the stencil/substrate separation ...
AIAA Journal, 1991
ABSTRACT
The development of a university scale source for intense beams of energetic, neutral atmospheric ... more The development of a university scale source for intense beams of energetic, neutral atmospheric species is discussed. An unconventional plasma source is used to produce a beam of ions that can be mass selected, focused, and slowed to appropriate energies. Subsequently, neutralization of the energetic ion stream is achieved by charge exchange collisions between the ion beam and molecules of