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Mervi Paulastokrockel - One of the best experts on this subject based on the ideXlab platform.
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localized recrystallization and cracking of lead free solder interconnections under thermal cycling
Journal of Materials Research, 2011Co-Authors: Hongtao Chen, Toni T Mattila, Maik Mueller, Xuwen Liu, Klausjuergen Wolter, Mervi PaulastokrockelAbstract:The failure mechanism of lead-free solder interconnections of chip scale package–sized Ball Grid Array (BGA) Component boards under thermal cycling was studied by employing cross-polarized light microscopy, scanning electronic microscopy, electron backscatter diffraction, and nanoindentation. It was determined that the critical solder interconnections were located underneath the chip corners, instead of the corner most interconnections of the package, and the highest strains and stresses were concentrated at the outer neck regions on the Component Side of the interconnections. Observations of the failure modes were in good agreement with the finite element results. The failure of the interconnections was associated with changes of microstructures by recrystallization in the strain concentration regions of the solder interconnections. Coarsening of intermetallic particles and the disappearance of the boundaries between the primary Sn cells were observed in both cases. The nanoindentation results showed lower hardness of the recrystallized grains compared with the non-recrystallized regions of the same interconnection. The results show that failure modes are dependent on the localized microstructural changes in the strain concentration regions of the interconnections and the crack paths follow the networks of grain boundaries produced by recrystallization.
Vincent P. Manno - One of the best experts on this subject based on the ideXlab platform.
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Optimized Thermoelectric Module-Heat Sink Assemblies for Precision Temperature Control
Journal of Electronic Packaging, 2012Co-Authors: Rui Zhang, Marc Hodes, David A. Brooks, Vincent P. MannoAbstract:Robust precision temperature control of heat-dissipating photonics Components is achieved by mounting them on thermoelectric modules (TEMs), which are in turn mounted on heat sinks. However, the power consumption of such TEMs is high. Indeed, it may exceed that of the Component. This problem is exacerbated when the ambient temperature and/or Component heat load vary as is normally the case. In the usual packaging configuration, a TEM is mounted on an air-cooled heat sink of specified thermal resistance. However, heat sinks of negligible thermal resistance minimize TEM power for sufficiently high ambient temperatures and/or heat loads. Conversely, a relatively high thermal resistance heat sink minimizes TEM power for sufficiently low ambient temperatures and heat loads. In the problem conSidered, total footprint of thermoelectric material in a TEM, thermoelectric material properties, Component operating temperature, relevant Component-Side thermal resistances, and ambient temperature range are prescribed. Moreover, the minimum and maximum rates of heat dissipation by the Component are zero and a prescribed value, respectively. Provided is an algorithm to compute the combination of the height of the pellets in a TEM and the thermal resistance of the heat sink attached to it, which minimizes the maximum sum of the Component and TEM powers for permissible operating conditions. It is further shown that the maximum value of this sum asymptotically decreases as the total footprint of thermoelectric material in a TEM increases. Implementation of the algorithm maximizes the fraction of the power budget in an optoelectronics circuit pack available for other uses. Use of the algorithm is demonstrated through an example for a typical set of conditions.
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optimized thermoelectric module heat sink assemblies for precision temperature control
ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems MEMS and NEMS: Volume 2, 2011Co-Authors: Rui Zhang, Marc Hodes, David A. Brooks, Matthew Van Lieshout, Vincent P. MannoAbstract:Robust precision temperature control of photonics Components is achieved by mounting them on thermoelectric modules (TEMs) which are in turn mounted on heat sinks. However, the power consumption of TEMs is high because high currents are driven through Bi2 Te3 -based semiconducting materials with high electrical resistivity and finite thermal conductivity. This problem is exacerbated when the ambient temperature surrounding a TEM varies in the usual configuration where the air-cooled heat sink a TEM is mounted to is of specified thermal resistance. Indeed, heat sinks of negligible and relatively high thermal resistances minimize TEM power consumption for sufficiently high and low ambient temperatures, respectively. Optimized TEM-heat sink assemblies reduce the severity of this problem. In the problem conSidered, total footprint of thermoelectric material in a TEM, thermoelectric material properties, heat load, Component operating temperature, relevant Component-Side thermal resistances and ambient temperature range are prescribed. Provided is an algorithm to compute the unique combination of the height of the pellets in a TEM and the thermal resistance of the heat sink attached to it which minimizes the maximum power consumption of the TEM over the specified ambient temperature range. This optimization maximizes the fraction of the power budget in an optoelectronics circuit pack available for other uses. Implementation of the algorithm is demonstrated through an example for a typical set of conditions.© 2011 ASME
J. K. Kivilahti - One of the best experts on this subject based on the ideXlab platform.
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Failure mechanisms of lead–free chip scale package interconnections under fast mechanical loading
2015Co-Authors: T. T. Mattila, J. K. KivilahtiAbstract:The reliability of chip scale package (CSP) Components against mechanical shocks has been studied by employing statistical, fractographic, and microstruc-tural research methods. The Components having high tin (Sn0.2Ag0.4Cu) solder bumps were reflow soldered with the Sn3.8Ag0.7Cu (wt.%) solder paste on Ni(P)|Au- and organic solderability preservative (OSP)–coated multilayer printed wiring boards (PWBs), and the assemblies were subjected to the stan-dard drop test procedure. The statistically significant difference in the reliability performance was observed: the Components soldered on Cu|OSP were more reliable than those soldered on Ni(P)|Au. Solder interconnections on the Cu|OSP boards failed at the Component Side, where cracks propagated through the (Cu,Ni)6Sn5 reaction layer, whereas interconnections on the Ni(P)|Au boards failed at the PWB Side exhibiting the brittle fracture known also as “black pad.” In the first failure mode, which is not normally observed in thermally cycled as-semblies, cracks propagate along the intermetallic layers due to the strong strain-rate hardening of the solder interconnections in drop tests. Owing t
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Failure mechanisms of lead-free chip scale package interconnections under fast mechanical loading
Journal of Electronic Materials, 2005Co-Authors: T. T. Mattila, J. K. KivilahtiAbstract:The reliability of chip scale package (CSP) Components against mechanical shocks has been studied by employing statistical, fractographic, and microstructural research methods. The Components having high tin (Sn0.2Ag0.4Cu) solder bumps were reflow soldered with the Sn3.8Ag0.7Cu (wt.%) solder paste on Ni(P)|Au- and organic solderability preservative (OSP)-coated multilayer printed wiring boards (PWBs), and the assemblies were subjected to the standard drop test procedure. The statistically significant difference in the reliability performance was observed: the Components soldered on Cu|OSP were more reliable than those soldered on Ni(P)|Au. Solder interconnections on the Cu|OSP boards failed at the Component Side, where cracks propagated through the (Cu,Ni)_6Sn_5 reaction layer, whereas interconnections on the Ni(P)|Au boards failed at the PWB Side exhibiting the brittle fracture known also as “black pad.” In the first failure mode, which is not normally observed in thermally cycled assemblies, cracks propagate along the intermetallic layers due to the strong strain-rate hardening of the solder interconnections in drop tests. Owing to strain-rate hardening, the stresses in the solder interconnections increase very rapidly in the corner regions of the interconnections above the fracture strength of the ternary (Cu,Ni)_6Sn_5 phase leading to intermetallic fracture. In addition, because of strain-rate hardening, the recrystallization of the as-soldered microstructure is hindered, and therefore the network of grain boundaries is not available in the bulk solder for cracks to propagate, as occurs during thermal cycling. In the black pad failure mode, cracks nucleate and propagate in the porous NiSnP layer between the columnar two-phase (Ni_3P+Sn) layer and the (Cu,Ni)_6Sn_5 intermetallic layer. The fact that the Ni(P)|Au interconnections fail at the PWB Side, even though higher stresses are generated on the Component Side, underlines the brittle nature of the reaction layer.
Radhakrishnan Pillai - One of the best experts on this subject based on the ideXlab platform.
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a phase 2 multicenter double blind randomized vehicle controlled clinical study to assess the safety and efficacy of a halobetasol tazarotene fixed combination in the treatment of plaque psoriasis
Journal of Drugs in Dermatology, 2017Co-Authors: Jeffrey L Sugarman, Linda Stein Gold, Mark Lebwohl, David M Pariser, Binu Alexander, Radhakrishnan PillaiAbstract:BACKGROUND: Psoriasis is a chronic, immune-mediated disease that varies widely in its clinical expression. Treatment options focus on relieving symptoms, reducing inflammation, induration, and scaling, and controlling the extent of the disease. Topical corticosteroids are the mainstay of treatment, however long-term safety remains a concern, particularly with the more potent formulations. Combination therapy with a corticosteroid and tazarotene may improve psoriasis signs at a lower corticosteroid concentration providing a superior safety profile. Objective To investigate the efficacy and safety of a once-daily application of a fixed combination halobetasol propionate 0.01% and tazarotene 0.045% (HP/TAZ) lotion in comparison with its monads and vehicle in subjects with moderate-to-severe plaque psoriasis. Methods Multicenter, randomized, double-blind, vehicle-controlled Phase 2 study in moderate or severe psoriasis (N=212). Subjects randomized (2:2:2:1 ratio) to receive HP/TAZ, individual monads, or vehicle, once-daily for 8 weeks. Efficacy assessments included treatment success (defined as at least a 2-grade improvement from baseline in the IGA score and a score of 'Clear' or 'Almost Clear'), and impact on individual signs of psoriasis (erythema, plaque elevation, and scaling) at the target lesion. Safety and treatment emergent adverse events (TEAEs) were evaluated throughout. Results HP/TAZ lotion demonstrated statistically significant superiority over vehicle as early as 2 weeks. At week 8, 52.5% of subjects had treatment success compared with 33.3%, 18.6%, and 9.7% in the HP (P=0.033), TAZ (P less than 0.001), and vehicle (P less than 0.001) groups, respectively. HP/TAZ lotion was superior to its monads and vehicle in reducing the psoriasis signs of erythema, plaque elevation, and scaling at the target lesion. At week 8, a 2-grade improvement in IGA was achieved by 54.2% of subjects for erythema, 67.8% for plaque elevation, and 64.4% for scaling. Most frequently reported TEAEs were application site reactions, and were more likely associated with the tazarotene Component. Side effects such as skin atrophy were rare. Conclusions HP/TAZ lotion was consistently more effective than its monads or vehicle in achieving treatment success and reducing psoriasis signs of erythema, plaque elevation, and scaling at the target lesion. Safety data were consistent with the known safety profile of halobetasol propionate and tazarotene, and did not reveal any new safety concerns with the combination product. J Drugs Dermatol. 2017;16(3):197-204. .
Pillai Radhakrishnan - One of the best experts on this subject based on the ideXlab platform.
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A Phase 2, Multicenter, Double-Blind, Randomized, Vehicle Controlled Clinical Study to Assess the Safety and Efficacy of a Halobetasol/Tazarotene Fixed Combination in the Treatment of Plaque Psoriasis
Henry Ford Health System Scholarly Commons, 2017Co-Authors: Sugarman, Jeffrey L, Stein Gold, Linda F, Lebwohl, Mark G, Pariser, David M, Alexander, Binu J, Pillai RadhakrishnanAbstract:BACKGROUND: Psoriasis is a chronic, immune-mediated disease that varies widely in its clinical expression. Treatment options focus on relieving symptoms, reducing inflammation, induration, and scaling, and controlling the extent of the disease. Topical corticosteroids are the mainstay of treatment, however long-term safety remains a concern, particularly with the more potent formulations. Combination therapy with a corticosteroid and tazarotene may improve psoriasis signs at a lower corticosteroid concentration providing a superior safety profile. OBJECTIVE: To investigate the efficacy and safety of a once-daily application of a fixed combination halobetasol propionate 0.01% and tazarotene 0.045% (HP/TAZ) lotion in comparison with its monads and vehicle in subjects with moderate-to-severe plaque psoriasis. METHODS: Multicenter, randomized, double-blind, vehicle-controlled Phase 2 study in moderate or severe psoriasis (N=212). Subjects randomized (2:2:2:1 ratio) to receive HP/TAZ, individual monads, or vehicle, once-daily for 8 weeks. Efficacy assessments included treatment success (defined as at least a 2-grade improvement from baseline in the IGA score and a score of \u27Clear\u27 or \u27Almost Clear\u27), and impact on individual signs of psoriasis (erythema, plaque elevation, and scaling) at the target lesion. Safety and treatment emergent adverse events (TEAEs) were evaluated throughout. RESULTS: HP/TAZ lotion demonstrated statistically significant superiority over vehicle as early as 2 weeks. At week 8, 52.5% of subjects had treatment success compared with 33.3%, 18.6%, and 9.7% in the HP (P=0.033), TAZ (P less than 0.001), and vehicle (P less than 0.001) groups, respectively. HP/TAZ lotion was superior to its monads and vehicle in reducing the psoriasis signs of erythema, plaque elevation, and scaling at the target lesion. At week 8, a 2-grade improvement in IGA was achieved by 54.2% of subjects for erythema, 67.8% for plaque elevation, and 64.4% for scaling. Most frequently reported TEAEs were application site reactions, and were more likely associated with the tazarotene Component. Side effects such as skin atrophy were rare. CONCLUSIONS: HP/TAZ lotion was consistently more effective than its monads or vehicle in achieving treatment success and reducing psoriasis signs of erythema, plaque elevation, and scaling at the target lesion. Safety data were consistent with the known safety profile of halobetasol propionate and tazarotene, and did not reveal any new safety concerns with the combination product