Evaluation of Thermal Resistance Matrix Method for an Embedded Power Electronic Module

Thermal characterization provides data on the thermal performance of electronic components under given cooling conditions. The most common thermal characterization parameter used to characterize the behavior of electronic components is the thermal resistance. In this work, experiments are conducted to obtain thermal characterization data for different chips in a multichip package. Using this data, it is shown that the assumption of a linear temperature rise with input power is valid within the expected range of operation of the electronic module. Secondly, the applicability of a resistance matrix superposition methodology to the packaging structure of an integrated power electronic module is evaluated. The temperatures and the associated uncertainties involved in using the resistance matrix superposition method are compared to those obtained directly by powering all chips. It is shown that for any arbitrary power losses from the chips, the resistance matrix superposition method can predict the temperatures of a multichip package with reasonable accuracy for temperature rise up to 50degC.     

Antenna pattern comparison between an outdoor cylindrical near-field test facility and an indoor spherical near-field antenna test facility

A new spherical near-field probe-positioning device has been designed and constructed, consisting of a large 5.0 meter fixed arc. This arc has been installed in a near-field test facility, located at Alenia Marconi Systems, on the Isle of Wight, UK. As part of the near-field qualification, testing was performed on a ground-based radar antenna. The resultant patterns were compared against measurements collected on the same antenna on a large outdoor cylindrical near-field test facility, also located on the Isle of Wight [F. Steiner et al., Jan. 1994]. These measurements included multiple-frequency measurements and multiple pattern comparisons. This paper summarizes the results obtained as part of the measurement program, and includes discussions on the error budgets for the two ranges, along with a discussion of the mutual error budget between the two ranges.     

Subpicosecond Domain Switching in Discrete Regions of Pb(Zr0.35Ti0.65)O3 Thick Films

The time dependence of the domain switching current density, J_sw(t), under pulsed voltages on a ferroelectric parallel‐plate capacitor is the consequence of region‐by‐region polarization reversals across the film. As the distributive coercive voltage of domain nucleation increases from zero to the maximum applied voltage during the capacitor charging time, J_sw(t) is proportional to the domain switching speed at each time. By transforming the spatially inhomogeneous domain nucleation distribution into a temporal distribution of coercive fields (E_c), a local lnJ_sw versus E_c^?1 plot is derived for each domain, following the Merz equation. This provides insight into the independent domain switching dynamics at different nucleation sites in Pb(Zr_0.35Ti_0.65)O₃ thick films over a large current range. Although the activation field of the slope of the lnJ_sw(t) versus E_c^?1 plot varies with film area and temperature, all the plots extrapolate to a single point (J₀, E₀) from which the ultimate domain switching current density of J₀ =1.4 × 10⁸ A cm^?2 at the highest field of E₀ = 0.20‐0.25 MV cm^?1 is derived. Unexpectedly, J₀ and E₀ are independent of the film thickness and area, after correction for a small interfacial‐layer effect. This analysis provides rigorous evidence for nucleation rate‐limited domain switching with a subpicosecond nucleation time and the relative unimportance of domain forward‐growth time across film thicknesses between 0.14 and 2 μm. This work paves the way to improve the efficiency of ferroelectric thick‐film functionality in electronic and optoelectronic devices with ultrafast clock rates.     

Modelling methodology for thermal analysis of hot solder dip process

The shift of electronics industry towards the use of lead-free solders in components manufacturing brought also the challenge of addressing the problem of tin whiskers. Manufacturers of high reliability and safety critical equipment in sectors such as defence and aerospace rely increasingly on the use of commercial-of-the-shelf (COTS) electronic components for their products and systems. The use of COTS components with lead-free solder plated terminations comes with the risks for their long term reliability associated with tin whisker growth related failures. In the case of leaded type electronic components such as Quad Flat Package (QFP) and Small Outline Package (SOP), one of the promising solutions to this problem is to “re-finish” the package terminations by replacing the lead-free solder coatings on the leads with conventional tin–lead solder. This involves subjecting the electronic components to a post-manufacturing process known as Hot Solder Dip (HSD). One of the main concerns for adopting HSD (refinishing) as a strategy to the tin whisker problem is the potential risk for thermally induced damage in the components when subjected to this process.     

Development of the high-pressure electro-dynamic gradient crystal-growth technology for semi-insulating CdZnTe growth for radiation detector applications

The high-pressure electro-dynamic gradient (HP-EDG) crystal-growth technology has been recently developed and introduced at eV PRODUCTS to grow large-volume, semi-insulating (SI) CdZnTe single crystals for room-temperature x-ray and gamma-ray detector applications. The new HP growth technology significantly improves the downstream CdZnTe device-fabrication yield compared to earlier versions of the HP crystal-growth technology because of the improved structural and charge-transport properties of the CdZnTe ingots. The new state-of-the-art, HP-EDG crystal-growth systems offer exceptional flexibility and thermal and mechanical stability and allow the growth of high-purity CdZnTe ingots. The flexibility of the multi-zone heater system allows the dynamic control of heat flow to optimize the growth-interface shape during crystallization. This flexibility combined with an advanced control system, improved system diagnostics, and realistic heat-transport modeling provides an excellent platform for continuing process development. Initial results on large-diameter (140 mm), SI Cd_1−xZn_xTe (x=0.1) ingots grown in low temperature gradients with the HP-EDG technique show reduced defect density and complete elimination of ingot cracking. The increased single-crystal yield combined with the improved charge transport allows the fabrication of large-volume, high-sensitivity, high energy-resolution detector devices at increased yield. The CdZnTe ingots grown to date produced large-volume crystals (≥1cm³) with electron mobility-lifetime product (μτ_e) in the (3–7) × 10⁻³ cm²/V range. The lower-than-desired charge-transport uniformity of the HP-EDG CdZnTe ingots is associated with the high density of Te inclusions formed in the ingots during crystallization. The latest process-development efforts show a reduction in the Te-inclusion density, an increase of the charge-transport uniformity, and improved energy resolution of the large-volume detectors fabricated from these crystals.     

Gas Diffusion,Energy Transport,and Thermal Accommodation in Single‐Walled Carbon Nanotube Aerogels

The thermal conductivity of gas‐permeated single‐walled carbon nanotube (SWCNT) aerogel (8 kg m^?3 density, 0.0061 volume fraction) is measured experimentally and modeled using mesoscale and atomistic simulations. Despite the high thermal conductivity of isolated SWCNTs, the thermal conductivity of the evacuated aerogel is 0.025 ± 0.010 W m^?1 K^?1 at a temperature of 300 K. This very low value is a result of the high porosity and the low interface thermal conductance at the tube–tube junctions (estimated as 12 pW K^?1). Thermal conductivity measurements and analysis of the gas‐permeated aerogel (H₂, He, Ne, N₂, and Ar) show that gas molecules transport energy over length scales hundreds of times larger than the diameters of the pores in the aerogel. It is hypothesized that inefficient energy exchange between gas molecules and SWCNTs gives the permeating molecules a memory of their prior collisions. Low gas‐SWCNT accommodation coefficients predicted by molecular dynamics simulations support this hypothesis. Amplified energy transport length scales resulting from low gas accommodation are a general feature of CNT‐based nanoporous materials.     

Design and demonstration of policy-based management in a multi-hop ad hoc network

In this paper, we propose a policy-based framework for the management of wireless ad hoc networks and briefly describe a characteristics-based taxonomy that provides a platform to analyze and compare different architectural choices. We develop a solution suite that helps achieve our goal of a self-organizing, robust and efficient management system. One of the main contributions of this work is the prototype implementation and testing of the mechanisms and protocols comprising our framework in a multi-hop ad hoc network environment. Experiments are conducted using both an emulated ad hoc network testbed and a true wireless testbed. Degradation in management system performance is observed as the number of hops between a policy server and client increases. Our proposed k-hop clustering algorithm alleviates this problem by limiting the number of hops between a server and client. We demonstrate the operation of our prototype implementation, illustrating QoS management in a multi-domain ad hoc network environment using the proposed cluster management, redirection, and policy negotiation mechanisms.     

An X-ray Radiography Study of the Effect of Thermal Cycling on Damage Evolution in Large-Area Sn-3.5Ag Solder Joints

There is a need for next-generation, high-performance power electronic packages and systems utilizing wide-band-gap devices to operate at high temperatures in automotive and electricity transmission applications. Sn-3.5Ag solder is a candidate for use in such packages with potential maximum operating temperatures of about 200°C. However, there is a need to understand the thermal cycling reliability of Sn-3.5Ag solders subject to such high-temperature operating conditions. The results of a study on the damage evolution occurring in large-area Sn-3.5Ag solder joints between silicon dies and direct bonded copper substrates with Au/Ni-P metallization subject to thermal cycling between 200°C and 5°C are presented in this paper. Interface structure evolution and damage accumulation were followed using high-resolution X-ray radiography, cross-sectional optical and scanning electron microscopies, and X-ray microanalysis in these joints for up to 3000 thermal cycles. Optical and scanning electron microscopy results showed that the stresses introduced by the thermal cycling result in cracking and delamination at the copper–intermetallic compound interface. X-ray microanalysis showed that stresses due to thermal cycling resulted in physical cracking and breakdown of the Ni-P barrier layer, facilitating Cu-Sn interdiffusion. This interdiffusion resulted in the formation of Cu-Sn intermetallic compounds underneath the Ni-P layer, subsequently leading to delamination between the Ni-rich layer and Cu-Sn intermetallic compounds.     

Nano‐Domain Pinning in Ferroelastic‐Ferroelectrics by Extended Structural Defects

Most ferroelectrics are also ferroelastics (hysteretic stress‐strain relationship and response to mechanical stresses). The interactions between ferroelastic twin walls and ferroelectric domain walls are complex and only partly understood, hindering the technological potential of these materials. Here we study via atomic force microscopy the pinning of 180‐degree ferroelectric domain walls in lead zirconate titanate (PZT). Our observations satisfy all three categories of ferroelectric‐ferroelastic domain interaction proposed by Bornarel, Lajzerowicz, and Legrand.