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Despite possible toxicity issues, chemical reduction or non-polarizable electrodes incorporated with highly reactive chemical species have been utilized to control the operational characteristics of organic electrochemical transistors (OECTs) for bioelectronic interfacing applications. In this study, we demonstrate that crosslinking between highly conductive poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and biocompatible nonconductive polyvinyl alcohol (PVA) effectively modulates the mixed conducting properties of PEDOT:PSS. The PEDOT:PSS–PVA films prepared by simple PEDOT:PSS and PVA blending at various ratios, spin-coating, crosslinking, and sulfuric acid treatment were comprehensively studied using optical spectroscopy, x-ray diffraction, atomic force microscopy, and electrical/electrochemical device characterizations. With PVA contents up to 20 wt.%, the resultant PEDOT:PSS–PVA-based OECTs showed a linear threshold voltage shift with a marginal loss of transconductance, suggesting an effective modulation of the peak transconductance gate voltage. Furthermore, the PVA content also affects the ion transport dynamics, which is related to the crystallite size and ionic functional group density in the PEDOT:PSS–PVA system. The detailed mechanism of delicately controlled mixed conduction in the PEDOT:PSS–PVA system is proposed from the perspective of structure-property relations.

The mechanical shock behavior of Sn–Ag–Bi–In (SABI) solder has been investigated by micro-Charpy impact test after subjecting the solder to high electric current stress. A trace amount of Co added (0.1 wt %) is used as a refiner in the SABI solder, and the joint soldered by conventional reflow exhibits a refined grain microstructure. The SABI+Co joint exhibits higher toughness, i.e., 70% more energy is absorbed during impact than a typical SABI joint. After 80 h of 20 A electric current applied at 160 °C, electromigration (EM) is observed in both the SABI and SABI+Co joints. However, the SABI+Co joint exhibits a constant mechanical strength, while the typical SABI joint exhibits a strength decreased by 16% at the Charpy absorption energy. The mechanical strength improved by Co addition implies that microstructure refinement is useful for enhancing the EM resistance of a solder joint structure for surface mount packaging.