Hierarchically porous polymer coatings for highly efficient passive daytime radiative cooling

Passive daytime radiative cooling (PDRC) involves spontaneously cooling a surface by reflecting sunlight and radiating heat to the cold outer space. Current PDRC designs are promising alternatives to electrical cooling but are either inefficient or have limited applicability. We present a simple, inexpensive, and scalable phase inversion–based method for fabricating hierarchically porous poly(vinylidene fluoride-co-hexafluoropropene) [P(VdF-HFP)HP] coatings with excellent PDRC capability. High, substrate-independent hemispherical solar reflectances (0.96 ± 0.03) and long-wave infrared emittances (0.97 ± 0.02) allow for subambient temperature drops of ~6°C and cooling powers of ~96 watts per square meter (W m−2) under solar intensities of 890 and 750 W m−2, respectively. The performance equals or surpasses those of state-of-the-art PDRC designs, and the technique offers a paint-like simplicity.

Deformation and Failure of Ultrafine-Grained Cu at Subambient Temperature

The ultrafine-grained copper was obtained by 12 passes of equal-channel angular pressing method. The uniaxial tensile tests at room temperature and the subambient temperature of 77 K show that the yield stress increases from the value of 128 MPa to the value of 138 MPa, respectively. In addition, the lowering the test temperature tends to the increase of the deformation before the failure. The fractographic analysis shows the transcrystalline ductile failure for all samples. Due to the high plasticity of nanostructured copper no influence of the nanoporosity on the failure process was observed.

New Method for Decapsulation of Copper Wire Devices Using LASER and Subambient Temperature Chemical Etch

IC packages have been greatly improved over the past several years. With the adoption of Cu wires and new green EMC (Epoxy Molding Compound), the suppression of lead, the use of Cu pillars and the increased number of dies, the verification of the quality of the assembly and failure analysis becomes critical. Starting twelve years ago, LASER ablation was introduced as a means to facilitate the pre-decapsulation of packages aiming at a completion by wet chemistry (acids) or dry chemistry (plasma). The decapsulation process with acid at medium temperature (75°C) does not permit to keep the Cu wires intact. Our studies and work in the past several years has consisted in lowering the temperature of acid use in order to minimize the effect of acid attack on the Al pads and Cu wires. Currently the thinnest wires used are 0.6 mil in diameter (approximately 15 μm). In this article we will demonstrate that decapsulations at sub-ambient temperatures are now possible and give expected results. Moreover, openings at near ambient temperature reduce the component deformation and also the deformation of its constituents compared to decapsulations at medium or high temperature.