Wafer-level packaging (WLP) is a next-generation semiconductor packaging technology that is important for realizing high-performance and ultra-thin semiconductor devices. However, the molding process, which is a part of the WLP process, has various problems such as a high defect rate and low predictability. Among the various defect factors, the die shift primarily determines the quality of the final product; therefore, predicting the die shift is necessary to achieve high-yield production in WLP. In this study, the die shift caused by the flow drag force of the epoxy molding compound (EMC) is evaluated from the die shift of a debonded molding wafer. Experimental and analytical methods were employed to evaluate the die shift occurring during each stage of the molding process and that resulting from the geometrical changes after the debonding process. The die shift caused by the EMC flow drag force is evaluated from the data on die movements due to thermal contraction/expansion and warpage. The relationship between the die shift and variation in the die gap is determined through regression analysis in order to predict the die shift due to the flow drag force. The results can be used for die realignment by predicting and compensating for the die shift.
A novel In−Sn−Bi solder with a low electrical resistivity of 14.3 × 10 −6 Ω cm and a melting temperature of 99.3 °C was produced for use in adhesive joining on a flexible poly(ethylene terephthalate) substrate. We determined that the fine microstructure of the In-based solder (which had an average phase size of 62.2 nm) strongly influenced its superplasticity and toughness at diffusive temperatures of 55−85 °C because the late-forming BiIn intermetallic compound (IMC) suppressed the growth of two other IMCs, In 3 Sn and In 0.2 Sn 0.8 , which formed earlier in the soldering process. Thus, an elongation of 858.3% and toughness of 36.0 MPa were obtained at a temperature of 85 °C and a strain rate of 0.0020 s −1 . However, due to phase boundary fracturing, the phase-refined solder exhibited a slightly more brittle nature (with an elongation of 74.3%) at room temperature compared with a standard In−Sn solder consisting only of the In 3 Sn and In 0.2 Sn 0.8 IMCs, which had a slightly larger phase size of 84.9 nm and higher ductility (with an elongation of 80.7%). In terms of superplastic deformation, the conventional fracture system based on the Hall−Petch effect transformed into phase boundary sliding at the solder operating temperature, significantly enhancing ductility.
Laser powder bed fusion (L-PBF)-processed 17-4 PH stainless steel (SS) generally exhibits a non-equilibrium microstructure consisting mostly of columnar δ-ferrite grains and a substantial fraction of retained austenite and martensite, contrary to 17-4 PH SS wrought with a fully martensite structure and coarse grains. Despite the different microstructures of L-PBF and wrought 17-4 PH SS, post-processing is typically performed using the conventional heat treatment method. The insufficient effect of the heat treatment on the L-PBF product produces a δ-ferrite phase in the microstructure. To obtain improved mechanical properties, the addition of a normalizing treatment to the conventional heat treatment after L-PBF in a nitrogen gas environment was investigated. The fully martensitic matrix developed by adding the normalizing treatment contained homogeneous Cu precipitates and exhibited a similar or improved strength and elongation to failure compared to the wrought SS.
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