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This study investigates surface oxidized layers of Cu-Fe-Zn-P (C194) and Cu-Ni-Si-Mg (C7025) lead frames under different oxidation conditions and their influence on the adhesion of epoxy molding compounds with lead frames. Micro-etching and electroplating are adopted to roughen the surface. Isothermal heat treatments which simulate molding and curing processes, as well as high temperature aging, are carried out to oxidize lead frame surface. According to the absorption peaks of FTIR (Fourier transform infrared spectroscopy) spectra, the topmost surface of the oxide layer can be easily identified. In combination with the reduction potential and time obtained from the coulometric reduction test, the variation of oxide phases along the through-thickness direction can also be revealed. Experimental results show that in addition to surface roughness, surface oxides and their thickness play more important roles in the interfacial strength between lead frames and epoxy molding compounds. In the case of the surface with one single Cu 2 O layer, an increase in oxide layer results in a decrease in bonding strength. Once the topmost surface forms CuO, the bonding strength could be enhanced due to a greater surface energy. Compared with electroplated C194, the thinner surface oxide layer and thus better performance in adhesion strength for electroplated C7025 can be ascribed to the immersion Ag surface treatment. • Surface oxidation layer of commercial lead frames was studied. • FTIR and electrochemical mean explored oxide on lead frame surface and underneath. • CuO formation leads to a greater EMC adhesion because of high surface energy. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogel‐based electronics are ideally suited for neural interfaces because they exhibit ultracompliant mechanical properties that match that of excitable tissue in the brain and peripheral nerve. Hydrogel‐based multielectrode arrays (MEAs) can conformably interface with tissues to minimize inflammation and improve the reliability to enhance signal transduction. However, MEA substrates composed of swollen hydrogels exhibit low toughness and poor adhesion when laminated on the tissue surface and also present incompatibilities with processes commonly used in MEA fabrication. Here, a strategy to fabricate an ultracompliant MEA is described based on aqueous‐phase transfer printing. This technique employs redox active adhesive motifs in hygroscopic polymer precursors that simultaneously form hydrogels through sol–gel phase transitions and bond to materials in the underlying microelectronic structures. Specifically, in situ gelation of four‐arm‐polyethylene glycol‐grafted catechol [PEG‐Dopa]4 hydrogels induced by oxidation using Fe3+ produces conformal adhesive contact with the underlying MEA, robust adhesion to electronic sub‐structures, and rapid dissolution of water‐soluble sacrificial release layers. MEAs are integrated on hydrogel‐based substrates to produce free‐standing ultracompliant neural probes, which are then laminated to the surface of the dorsal root ganglia in feline subjects to record single‐unit neural activity. [ABSTRACT FROM AUTHOR]

The use of scaled-down micro-bumps in miniaturized consumer electronic products has led to the easy realization of full intermetallic solder bumps owing to the completion of the wetting layer. However, the direct contact of the intermetallic compounds (IMCs) with the adhesion layer may pose serious reliability concerns. In this study, the terminal reaction of the Ti adhesion layer with Cu–Sn IMCs was investigated by aging the micro-bumps at 200 °C. Although all of the micro-bumps transformed into intermetallic structures after aging, they exhibited a strong attachment to the Ti adhesion layer, which differs significantly from the Cr system where spalling of IMCs occurred during the solid-state reaction. Moreover, the difference in the diffusion rates between Cu and Sn might have induced void formation during aging. These voids progressed to the center of the bump through the depleting Cu layer. However, they neither affected the attachment between the IMCs and the adhesion layer nor reduced the strength of the bumps. In conclusion, the IMCs demonstrated better adhesive behavior with the Ti adhesion layer when compared to Cr, which has been used in previous studies. [ABSTRACT FROM AUTHOR]