Aicha Elshabini

An overview to integrated power module design for high power electronics packaging

Abstract In recent years, there has been an explosion in demand for smaller and lighter, more efficient, and less expensive power electronic supplies and converters. There are a number of reasons for this recent necessity, ranging from the need for smaller and cheaper power converters for consumer electronics (such as laptop computers and cellular phones) to the need for highly reliable power electronics for such items as satellite and military craft power systems, which are required to be highly efficient, light in weight, smaller in volume, and low cost. This paper discusses the concept of Integrated Power Modules (IPMs), in which the electronic control circuitry and the high power electronics of the converter are integrated into a single compact standardized module. The advantages and disadvantages of such an approach will be discussed in reference to the current industry standard for power electronics design and packaging. The researchers will then take the readers through the IPM design, including basic circuit topology layout, module fabrication processes, and finally thermal considerations.

Fabrication of microvias for multilayer LTCC substrates

Advances in screen printing and photoimageable paste technologies have allowed low-temperature cofired ceramic (LTCC) circuit densities to continue to increase; however, the size of vias for Z-axis interconnections in multilayer LTCC substrates have been a limiting process constraint. In order to effectively exploit the 50-100-/spl mu/m line/spacing capabilities of advanced screen printing and photoimageable techniques, microvia technologies need to achieve 100 /spl mu/m and under in diameter. Three main steps in fabrication of microvias include via formation, via metallization or via fill, and layer-to-layer alignment. The challenges associated with the processing and equipment for the fabrication of microvias are addressed in this paper. Microvias down to 50 /spl mu/m in diameter with spacings as small as 50 /spl mu/m are achieved in 50-254-/spl mu/m-thick LTCC tape layers through the use of a mechanical punching system, whereas the minimum size of 75-/spl mu/m via/spacing is obtained using a pulse laser-drilling system in the LTCC tape layers with the same thicknesses as those for the punching test. The quality of punched microvias and laser-drilled microvias will be presented as well. Layer-to-layer alignment is crucial to the connection of vias in adjacent LTCC tape layers. Through a stack and tack machine with a three-camera vision system and an adjustable precision stage, less than 25-/spl mu/m layer-to-layer misalignment is achieved across a 114.3/spl times/114.3 mm (4.5/spl times/4.5 in) design area. In a six-layer LTCC test substrate (152/spl times/152/spl times/0.762 mm), microvias of 50, 75, and 100 /spl mu/m in diameter are successfully fabricated without the use of via catch pads. The cross section of fired microvias filled with silver conductor pastes at various locations of this substrate demonstrates a minor layer-to-layer misalignment in both X and Y directions across the substrate.

Ceramic Interconnect Technology Handbook

Ceramics were among the first materials used as substrates for mass-produced electronics, and they remain an important class of packaging and interconnect material today. Most available information about ceramic electronics is either outdated or focused on their materials science characteristics. The Ceramic Interconnect Technology Handbook goes beyond the traditional approach by first surveying the unique properties of ceramics and then discussing design, processing, fabrication, and integration, as well as packaging and interconnect technologies. Collecting contributions from an outstanding panel of experts, this book offers an up-to-date overview of modern ceramic electronics, from design and material selection to manufacturing and implementation. Beginning with an overview of the development, properties, advantages, and applications of ceramics, coverage spans electrical design, testing, simulation, thermomechanical design, screen printing, multilayer ceramics, photo-defined and photo-imaged films, copper interconnects for ceramic substrates, and integrated passive devices in ceramic substrates. It also offers a detailed review of the surface, thermal, mechanical, and electrical properties of various ceramics as well as the processing of high- and low-temperature cofired ceramic (HTCC and LTCC) substrates. Opening new vistas and avenues of advancement, the Ceramic Interconnect Technology Handbook is the only source for comprehensive discussion and analysis of nearly every facet of ceramic interconnect technology and applications.

Interfacial thermal resistance and temperature dependence of three adhesives for electronic packaging

The thermal resistance and its temperature dependence was measured for three industrial adhesives used for electronic packaging. Measurements were made by the laser-flash method from room temperature to 300/spl deg/C. The samples were in the form of sandwiches consisting of two platelets of silicon carbide-reinforced aluminum (AlSiC) bonded together with the adhesives. The total thermal resistance of the bond (the sum of the bulk thermal resistance of the adhesive and the resistances at the two interfaces) was calculated from the thermal response of the sandwich subjected on one side to a single laser-flash. The total thermal resistance was found to decrease with increasing temperature. The bulk thermal resistance of the adhesive, calculated from its thickness and independently determined thermal conductivity, was found to be relatively independent of temperature. The interfacial resistance at the AlSiC interfaces, depending on the adhesive, ranged from about 60 to 80% of the total resistance decreasing to about 50% of the total interfacial resistance at 300/spl deg/C. For two of the adhesives considered in this study, the interfacial thermal resistances for the AlSiC/adhesive interfaces were found to be considerably higher than those found in an earlier study of Si/adhesive interfaces.

Low cost flex substrates for miniaturized electronic assemblies

Abstract Electronic power converters have been designed, produced, and disseminated to the market in mass quantities utilizing a number of fabrication techniques; ranging from standard printed circuit board (PCB) technologies for low cost applications, to conventional thick film on ceramic, to direct bond copper (DBC) approaches for high power, higher cost applications. Each of these approaches holds a share of the power packaging market, but they all demonstrate a limitation to conventional two dimensional “flat board” strategy. PCBs, thick films, and DBCs are all technologies which restrict, for the most part, circuit and package designs to two dimensional boards. The one potential pathway into the third dimension is through the use of multilayers; an approach, which becomes increasingly difficult with each additional layer added beyond the first, and with the exception of high performance solutions is typically cost prohibitive for the majority of applications. This paper will demonstrate the feasibility and viability of flexible polymer substrates. Flex technology employs industry standard PCB and/or thick film processes, offers the lower cost, higher performance solutions inherent with the majority of polymer plastics, and as a final bonus, essentially frees the designer to more efficiently utilize all three dimensions of space. The researchers have demonstrated the feasibility of this low cost alternative solution through the fabrication and testing of integrated power modules, which utilize flexible polymer substrates in conjunction with both surface mount and bare dice. These DC/DC power converters transform 120 V/240 V inputs to 9 V, 7-W outputs, and illustrate through their unique geometrical design the miniaturization advantages of fully utilizing the three dimensional space offered by flex circuitry.

An interdigital bandpass filter embedded in LTCC for 5-GHz wireless LAN applications

This letter presents a compact interdigital stripline bandpass filter embedded in low temperature cofired ceramic for 5-GHz wireless LAN applications, including design, simulation, fabrication, and measurements. The filter measures 8 mm/spl times/7 mm/spl times/1.1 mm and exhibits an insertion loss of 3.6 dB, a return loss of 20 dB, and a 212-MHz passband with the midband frequency at 5.28 GHz. The filter is highly reproducible with good tolerance. A low noise amplifier (LNA) built on the top of the LTCC substrate with an embedded filter has the same bandwidth and midband frequency as those of the filter. Using this filter and an integrated chip, a small RF front-end receiver has been achieved.

Polymer thick film (PTF) and flex technologies for low cost power electronics packaging

Electronic power converters have been designed, produced, and disseminated in mass quantities using a number of fabrication techniques, from standard PCB technologies for low cost applications, to thick film on ceramic, to direct bond copper (DBC) for high power, higher cost applications. Each approach holds a share of the power packaging market, but they all restrict, for the most part, circuit and package designs to 2D boards. One potential pathway into the third dimension is by the use of multilayers, an approach which becomes increasingly difficult with each additional layer added beyond the first, and with the exception of high performance solutions is typically cost prohibitive for the majority of applications. This paper demonstrates the feasibility and viability of an alternative low cost power packaging option which uses familiar industry technologies in a unique manner: flexible polymer substrates. Flex technology uses industry standard PCB and/or thick film processes, offers the lower cost, higher performance solutions inherent with the majority of polymer plastics, and as a final bonus, frees the designer to more efficiently use all three dimensions. The researchers have shown the feasibility of this low cost alternative solution through the fabrication and testing of integrated power modules (IPMs) which use flex polymer substrates in conjunction with both surface mount and bare dice. These DC/DC power converters transform 120 V/240 V inputs to 9V, 7 W outputs, and illustrate the miniaturization advantages of fully utilizing the 3D space offered by flex circuitry.

Computer Modeling of Liquid Droplet Impact on Heat Transfer During Spray Cooling

Spray cooling is a high flux heat removal technique considered for systems dissipating high power within small areas such as advanced lasers. Recently Selvam and Ponnappan (2004 & 2005) identified the importance of modeling heat transfer in a thin liquid film on a hot surface at the micro level and illustrated how this micro level modeling could help to improve the macro level spray cooling. The goal of this research is to advance the theoretical understanding of spray cooling to enable efficient system level hardware designs. Two-phase flow modeling is done using the level set method to identify the interface of vapor and liquid. The modifications made to the incompressible Navier-Stokes equations to consider surface tension and phase change are presented. The equations are solved using the finite difference method. The effect of liquid droplet impact on a 40 μm thick liquid film containing vapor bubble and the consequent heat removal is explained with a sequence of temperature vs. time contours. From that, the importance of fast transient conduction in the liquid film leading to high heat flux in a short time is illustrated. The optimum positioning of the droplet with respect to the vapor bubble for effective heat removal is also systematically investigated. This information is expected to help in proper positioning of the droplet in three-dimensional modeling.Copyright

A novel packaging methodology for spray cooling of power semiconductor devices using dielectric liquids

The heat flux requirements of present power electronics systems are exceeding 100 W/cm2 and are predicted to reach the 1000 W/cm2 range in the near future. Spray cooling is a cooling technology that can provide such enormous cooling demands. Direct spray cooling of power devices (e.g., IGBTs) that are conventionally wire-bonded creates long-term reliability problems. So in order to achieve the expected future heat load demands and improve the reliability of the system there is a need for novel packaging methodologies. This paper reports on an innovative packaging methodology and a test vehicle that demonstrates the potential of spray cooling power electronics. This paper describes the proposed methodology as well as the spraying parameters that affect the cooling

Getting aggressive with passive devices

The circuit boards of many mixed-signal and digital systems are now dominated by individually placed discrete passive (DP) components. This article looks at thin-film integrated passives (IPs) as an alternative to DPs in the effort to save board space and improve electrical performance and system reliability. Integrated passive components have been utilized successfully with ceramic substrate technology for over 50 years in the form of thick-film resistive and dielectric firable pastes. However, this considerable infrastructure cannot be transferred to FR4 and flex substrates due to the high firing temperatures required, and these board materials make up the vast majority of interconnect substrates, in consumer and commercial systems. Mmat has been lacking is thin-film IP materials and fabrication processes that are compatible with organic boards.