Abnormal Shear Performance of Microscale Ball Grid Array Structure Cu/Sn–3.0Ag–0.5Cu/Cu Solder Joints with Increasing Current Density

The shear performance and fracture behavior of microscale ball grid array structure Cu/Sn–3.0Ag–0.5Cu/Cu solder joints with increasing electric current density (from 1.0 × 103 to 6.0 × 103 A/cm2) at various test temperatures (25 °C, 55 °C, 85 °C, 115 °C, 145 °C, and 175 °C) were investigated systematically. Shear strength increases initially, then decreases with increasing current density at a test temperature of no more than 85 °C; the enhancement effect of current stressing on shear strength decreases and finally diminishes with increasing test temperatures. These changes are mainly due to the counteraction of the athermal effect of current stressing and Joule heating. After decoupling and quantifying the contribution of the athermal effect to the shear strength of solder joints, the results show that the influence of the athermal effect presents a transition from an enhancement state to a deterioration state with increasing current density, and the critical current density for the transition decreases with increasing test temperatures. Joule heating is always in a deterioration state on the shear strength of solder joints, which gradually becomes the dominant factor with increasing test temperatures and current density. In addition, the fracture location changes from the solder matrix to the interface between the solder matrix and the intermetallic compound (IMC) layer (the solder/IMC layer interface) with increasing current density, showing a ductile-to-brittle transition. The interfacial fracture is triggered by current crowding at the groove of the IMC layer and driven by mismatch strain at the solder/IMC layer interface, and the critical current density for the occurrence of interfacial fracture decreases with increasing test temperatures.

Preparation of Ideally Ordered Anodic Porous Alumina by Prepatterning Process Using a Flexible Mold

Ideally ordered anodic porous alumina with controlled interpore distances was formed by fabricating a resist mask using a flexible mold and subsequent anodization. Prior to forming the resist pattern on the surface of an Al substrate, Al was pre-anodized at 10 V to prepare the fine porous structure, which acts as a resist adhesive layer. After the formation of the resist mask using a flexible mold, an arranged array of cavities with Al exposed at the bottom was formed by the selective dissolution of the oxide layer at resist openings. The subsequent anodization of the sample with the cavity array generated ideally ordered anodic porous alumina because alumina holes were formed at the bottom of cavities during anodization. This process allows the preparation of ideally ordered anodic porous alumina even on a curved Al surface owing to the flexibility of the mold. In addition, this process can also be applied to the preparation of an ideally ordered anodic porous alumina with a large sample area because the Al substrate can be patterned without high pressure. The obtained sample can be used for various applications requiring an ideally ordered hole array structure.

Bimetallic ZnCo nanorod array for highly reactive and durable hydrogen evolution reaction

One-step hydrothermal method to synthesize a stable ZnCo2(OH)F nanorod array structure supported by nickel foam.

Ordered Porous TiO2@C Layer as an Electrocatalyst Support for Improved Stability in PEMFCs

Proton exchange membrane fuel cells (PEMFCs) are the most promising clean energy source in the 21st century. In order to achieve a high power density, electrocatalytic performance, and electrochemical stability, an ordered array structure membrane electrode is highly desired. In this paper, a new porous Pt-TiO2@C ordered integrated electrode was prepared and applied to the cathode of a PEMFC. The utilization of the TiO2@C support can significantly decrease the loss of catalyst caused by the oxidation of the carbon from the conventional carbon layer due to the strong interaction of TiO2 and C. Furthermore, the thin carbon layer coated on TiO2 provides the rich active sites for the Pt growth, and the ordered support and catalyst structure reduces the mass transport resistance and improves the stability of the electrode. Due to its unique structural characteristics, the ordered porous Pt-TiO2@C array structure shows an excellent catalytic activity and improved Pt utilization. In addition, the as-developed porous ordered structure exhibits superior stability after 3000 cycles of accelerated durability test, which reveals an electrochemical surface area decay of less than 30%, considerably lower than that (i.e., 80%) observed for the commercial Pt/C.