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For the fine‐pitch application of flip‐chip bonding with semiconductor packaging, fluxing and hybrid underfills were developed. A micro‐encapsulated catalyst was adopted to control the chemical reaction at room and processing temperatures. From the experiments with a differential scanning calorimetry and viscometer, the chemical reaction and viscosity changes were quantitatively characterized, and the optimum type and amount of micro‐encapsulated catalyst were determined to obtain the best pot life from a commercial viewpoint. It is expected that fluxing and hybrid underfills will be applied to fine‐pitch flip‐chip bonding processes and be highly reliable.

The rapid progress in silicon carbide (SiC)-based technology for high-power applications expects an increasing operation temperature (up to 250 °C) and awaits reliable packaging materials to unleash their full power. Epoxy-based encapsulant materials failed to provide satisfactory protection under such high temperatures due to the intrinsic weakness of epoxy resins, despite their unmatched good adhesion and processability. Herein, we report a series of copolymers made by melt blending novolac cyanate ester and tetramethylbiphenyl epoxy (NCE/EP) that have demonstrated much superior hightemperature stability over current epoxies. Benefited from the aromatic, rigid backbone and the highly functional nature of the monomers, the highest values achieved for the copolymers are as follows: glass-transition temperature (T g ) above 300 °C, decomposition onset above 400 °C, and char yield above 45% at 800 °C, which are among the highest of the known epoxy chemistry by far. Moreover, the high-temperature aging (250 °C) experiments showed much reduced mass loss of these copolymers compared to the traditional high-temperature epoxy and even the pure NCE in the long term by suppressing hydrolysis degradation mechanisms. The copolymer composition, i.e., NCE to EP ratio, has found to have profound impacts on the resin flowability, thermomechanical properties, moisture absorption, and dielectric properties, which are discussed in this paper with in-depth analysis on their structure−property relationships. The outstanding high-temperature stability, preferred and adjustable processability, and the dielectric properties of the reported NCE/EP copolymers will greatly stimulate further research to formulating robust epoxy molding compounds (EMCs) or underfill for packaging next-generation high-power electronics.

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Popular solder-bumping mechanisms such as electroplating and stencil printing suffer from either high process costs or technical limitations. A low-cost solder-on-pad (SoP) process has been developed to meet the requirements of fine-pitch solder bumping. This paper focuses on the characterization and estimation of the SoP process. To form a solder bump without soldering defects, optimum process conditions should be carefully designed. A model to estimate the bump volume and predict the bump height is suggested. By optimizing the composition of solder paste material called solder-bump-maker, and by adjusting the process conditions, Sn-Ag-Cu solder bumps with different heights are obtained. The experiments and analysis to understand the impact of parameters were based on test vehicles with 80 μm pitch size. Then, the measured heights of solder bumps are compared with the model to see how they fit the estimation. Finally, a similar process has been conducted to test vehicles with pitch sizes of 150 and 40 μm, to confirm the scalability of the SoP process in different pitch sizes.