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Silver sintering technology has received considerable attention in recent years because it has the potential to be a suitable interconnection material for high-temperature power electronic packaging, such as high melting temperature, high electrical/thermal conductivity, and excellent mechanical reliability. It should be noted, however, that pressure (usually between three to five MPa) was added during the sintering stage for attaching power chips with area larger than 100 mm2. This extra pressure increased the complexity of the sintering process. The maximum chip size processed by pressure-free sintering, in the published resources, was 6 x 6 mm2. One objective of this work was to achieve chip-attachment with area of 13.5 x 13.5 mm2 (a chip size of one kind of commercial IGBT) by pressure-free sintering of nano-silver paste. Another objective was to fabricate high-power (1200 V and 150 A) multi-chip module by pressure-free sintering. In each module (half-bridge), two IGBT dies (13.5 x 13.5 mm2) and two diode dies (10 x 10 mm2) were attached to a DBC substrate. Modules with solder joints (SN100C) and pressure-sintered silver joints were also fabricated as the control group. The peak temperature in the process of of pressure-free sintering of silver was around 260oC, whereas 270oC for vacuum reflowing of solder, and 280oC under three MPa for pressure-sintering of silver. The process for wire bonding, lead-frame attachment, and thermocouple attachment are also recorded. Modules with the above three kinds of joints were first characterized by electrical methods. All of them could block 1200 V DC voltage after packaging, which is the voltage rating of bare dies. Modules were also tested up to the rated current (150 A) and half of the rated voltage (600 V), which were the test conditions in the datasheet for commercial modules with the same voltage and current ratings. I-V characteristics of packaged devices were similar (on-resistance less than 0.5 mohm). All switching waveforms at transient stage (both turn-on and turn-off) were clean. Six switching parameters (turn-on delay, rise time, turn-off delay, fall time, turn-on loss, and turn-off loss) were measured, which were also similar (<9%) among different kinds of modules. The results from electrical characterizations showed that both static characterizations and double-pulse test cannot be used for evaluating the differences among chip-attach layers. All modules were also characterized by their thermal performances. Transient thermal impedances were measured by gate-emitter signals. Two setups for thermal impedance measurement were used. In one setup, the bottoms of modules were left in the air, and in the other setup, bottoms of modules were attached to a chiller (liquid cooling and temperature controlled at 25oC) with thermal grease. Thermal impedances of three kinds of modules still increased after 40 seconds for the testing without chiller, since the thermal resistance of heat convection from bottom copper to the air was included , which was much larger than the sum of the previous layers (from IGBT junction, through the chip-attach layer, to the bottom of DBC substrate). In contrast, thermal impedances became almost stable (less than 3%) after 15 seconds for all modules when the chiller was used. Among these three kinds of modules, the module with pressure sintered joints had the lowest thermal impedance and the thermal resistance (tested with the chiller) around 0.609oK/W, In contrast, the thermal resistance was around 964oK /W for the soldered module, and 2.30oK /W for pressure-free sintered module. In summary, pressure-free large-area sintered joints were achieved and passed the fabrication process for IGBT half-bridge module with wiring bonding. Packaged devices with these kinds of joints were verified with good electrical performance. However, thermal performances of pressure-free joints were worse than solder joints and pressure-sintered joints. / Master of Science

Electrical switches are ubiquitous. Performance requirement for a switch is stringent. The operating mechanism mostly decides the performance of an electromechanical switch. However, design of such mechanisms, which involve discontinuous motions, is not much addressed in literature. The present work proposes a systematic procedure to design and analyze toggle based switching mechanisms. The work defined the toggle phenomenon rigorously, and, based on the behaviour of the toggles, provided a classification scheme for the switch mechanisms. The existing switches fall in two major categories viz., single-toggle and double-toggle switches. The double toggle mechanism is more suitable for high power breaking as it can isolate the system’s behaviour from the operator’s behaviour. The kinematic and geometric attributes of the operating mechanism which affect the toggle sequence and timings have been identified. A systematic simulation based study has been performed to identify the influence of different kinematic and dynamic parameters on the functionality of a double toggle switching mechanism. The influence of the variable moment of inertia and mechanism singularities arising out of introduction of the four bar sub chain on the performance of the system have been studied in detail. It is observed that the performance of the double toggle systems is less susceptible, though not immune to the user behaviour; in extreme scenarios the switching performance could become erratic. The use of an additional spring in an existing system enhanced the system performance; but, connecting the main spring with the coupler link altered the system performance more dramatically. Thus it established that the influence of the kinematic configuration on the performance of a switching mechanism is more pronounced than the dynamic characteristics of a comparable system. For the ab initio design of double toggle switching mechanisms, necessary structural criteria for a mechanism to exhibit double toggle phenomenon have been identified and verified with various 2 d.o.f. systems. It is also established that any double toggle mechanism cannot be used directly as a switching mechanism; the link dimensions, link arrangements and the stopper locations have to be chosen properly. Towards that end, three necessary kinematic criteria for a switching mechanism are identified. A few mechanisms which satisfy all structural and kinematic criteria are identified; the switching and toggle behaviour of these mechanisms are examined through simulations using Pro/Mechanism. Finally, considering all the conditions a is constructed with consideration of mass and geometric shape of the links. Thus, it established that the proposed methodology can systematically generate novel, structurally distinct electrical switches.

The Catalyst 6500 is a modern commercial switch, capable of processing millions of packets per second through the utilization of specialized hardware. One of the main hardware components aiding the switch in performing its task is the Ternary Content Addressable Memory (TCAM). TCAMs update themselves with data relevant to routing and switching based on the traffic flowing through the switch. This enables the switch to forward future packets destined to a location that has already been previously discovered - at a very high speed. The problem is TCAMs have a limited size, and once they reach their capacity, the switch has to rely on software to perform the switching and routing - a much slower process than performing Hardware Switching that utilizes the TCAM. A framework has been developed to analyze the switch’s performance once the TCAM has reached its capacity, as well as measure the penalty associated with a cache miss. This thesis concludes with some recommendations and future work.

The Catalyst 6500 is a modern commercial switch, capable of processing millions of packets per second through the utilization of specialized hardware. One of the main hardware components aiding the switch in performing its task is the Ternary Content Addressable Memory (TCAM). TCAMs update themselves with data relevant to routing and switching based on the traffic flowing through the switch. This enables the switch to forward future packets destined to a location that has already been previously discovered - at a very high speed. The problem is TCAMs have a limited size, and once they reach their capacity, the switch has to rely on software to perform the switching and routing - a much slower process than performing Hardware Switching that utilizes the TCAM. A framework has been developed to analyze the switch’s performance once the TCAM has reached its capacity, as well as measure the penalty associated with a cache miss. This thesis concludes with some recommendations and future work.