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Gallium Oxide (Ga 2 O 3) holds significant potential for the next generation of electronic devices following SiC and GaN due to its ultra-wide bandgap of approximately 4.5 eV - 4.9 eV and high theoretical critical breakdown field strength of 8 MV/cm. Nonetheless, Ga 2 O 3 has a naturally low thermal conductivity, resulting in limited device output performance and hindering Ga 2 O 3 devices from reaching their full theoretical potential. In this study, we demonstrate that the appropriate thermal management strategy can solve the above challenges. By comparing the thermal control schemes including the Ga 2 O 3 FET devices on the original substrate, the thinned Ga 2 O 3 substrate, the high thermal conductivity substrate, the heat sink packaging, and the flip-chip packaging, it is demonstrated that the flip-chip model is the most effective strategy to improve the heat dissipation performance of the Ga 2 O 3 device. By utilizing the appropriate carrier in flip-chip packaging, the temperature elevation of the device at 2 W/mm power density will be diminished by around 91% in contrast to the initial basic device. Furthermore, the output performance of the device demonstrates significant enhancement. This thermal management technique successfully resolves the severe heat dissipation issue prevalent in Ga 2 O 3 devices and eliminates primary obstacles concerning the industrialization of Ga 2 O 3 RF and power devices. • Establishing a thermoelectric coupling model to solve the problem of Ga 2 O 3 transistor thermal management. • Replacing the native substrate is not an optimal solution to the thermal problem of Ga 2 O 3 transistors. • The chip flip packaging can greatly improve the heat dissipation performance of Ga 2 O 3 devices. [ABSTRACT FROM AUTHOR]

Microelectromechanical systems (MEMS)-type double helix chip-level electrical interconnect structures are fabricated and characterized in this paper. Due to their springlike structure, double helix interconnects have the potential to provide large mechanical compliance to compensate for nonidealities, such as nonplanarity and thermal expansion mismatch between silicon chips and substrates. A double helix configuration provides for structures with a high volumetric density of conductor for enhanced current carrying capability. The fabrication process is compatible with wafer-level fabrication and packaging. Instead of using solder to form semipermanent interconnections, the double helix interconnects use pressure to make electrical connection and provide sufficiently low resistance (~35 ± 15 mΩ). Large arrays of double helix structures have been fabricated and characterized with excellent yield. The mechanical and electrical models of the structures are presented. Reworkability tests were performed and the structures show a consistent resistance over 50 remating cycles. [ABSTRACT FROM AUTHOR]

Electronics packaging based on stress-engineered spring interconnects has the potential to enable integrated IC testing, fine pitch, and compliance not readily available with other technologies. We describe new spring contacts which simultaneously achieve low resistance (<100~m\Omega) and high compliance (>30~\mum) in dense 2-D arrays (180–180-\mum pitch). Mechanical characterization shows that individual springs operate at approximately 150-\muN force. Electrical measurements and simulations imply that the interface contact resistance contribution to a single contact resistance is <40~m\Omega. A daisy-chain test die consisting of 2844 contacts is assembled into flip-chip packages with 100% yield. Thermocycle and humidity testing suggest that packages with or without underfill can have stable resistance values and no glitches through over 1000 thermocycles or 6000 h of humidity. This paper suggests that integrated testing and packaging can be performed with the springs, enabling new capabilities for markets such as multichip modules. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an innovative polishing process aimed at leveling rough surface of plating-based flip chip solder bumps so as to get uniform coplanarity across the whole substrate after both electroplating and reflow processes. This polishing mechanism is characteristic of combining mechanical-dominated polishing force with slight chemical reaction together. A large number of extremely but inevitably rugged mushroom-like structures after electroplating are drastically smoothed down with the help of this newly-developed polishing process. Nearly 70μm solder bumps in height with two different profiles as square and circle on the substrates reach as flatly as ±3μm between different substrates after reflow process; ±2.5μm in single substrate; and even ±1μm in die, respectively. Besides, surface roughness among the solder bumps is simultaneously narrowed down from Ra 0.6 to Ra 0.03 along with the coplanarity improvement. Excellent uniformity and smooth surface roughness in solder bumps are absolutely beneficial to pile up and deposit in the following steps in MEMS and semiconductor fields. [Copyright &y& Elsevier]

Abstract: A novel method (the V-shaped curve) is presented to predict the failure probability of anisotropic conductive film (ACF) in IC/substrate assemblies. The Poisson function is used to calculate the probability of opening failure in the vertical gap between the pads, while the box and modified box models are used to estimate the probability of bridging failure between the pads in the pitch direction. The opening and bridging probabilities are combined using probability theory to establish four different failure prediction models. The results reveal that the model combining the Poisson function for fewer than six particles per pad with the modified box model provides the most accurate predictions of the failure probability of ACF in IC/substrate assemblies. [Copyright &y& Elsevier]