August 2019 – Paul Wu's Blog

Foam compression set

Compression set is an important parameter to evaluate the foam’s permanent deflection which determines the long term performances,. e.g. sealing, isolation.

A method to reduce nodules on ED copper foil

ED copper foil is broadly used in Li-ion battery and printed circuit boards in electronics industry. However, nodules are commonly observed on the surface of ED copper foil made through a conventional electro-deposition method. Patent of US 9,562.298 B2 teaches a new way to reduce the number of the nodules on the surface.

Liquid metal

For liquid metals, people may immediately think of mercury; in fact there are several other metals with melting point close to room temperature in addition to Mercury (Hg, MP=−38.8 °C, e.g. Caesium(Cs, MP=28.5 °C, Rubidium (Rb, MP=39 °C, Francium (Fr, estimated MP= at 27 °C), and Gallium (Ga, MP=30 °C). However, due to the issues of radioactivity, vapor pressure, and toxicity, etc, the practical liquid metal is typically Ga based eutectic alloy with melting point less than that of Ga.

Accuracy of Steady State Thermal conductivity measurement

The steady state method is commonly adopted to measure thermal resistance and conductivity of thermal interface materials or TIMs. A heat flow through the TIM is generated and the temperature gradient across the TIM is measured, and the thermal resistance or conductivity can be calculated through the procedure defined by ASTM standard ASTM D5470.

Cyclic voltammetry

Cyclic voltammeter is frequently adopted to study electron transfer in electrochemistry, battery, electrochromic, semiconducting devices fields.

Thermal contact resistance & TIM measurement

Heat flow method can be adopted to measure the thermal contact resistance of two mating samples or thin film materials.

Raman spectroscopy

Once a laser illuminates on a specimen, photons of the laser beam will be absorbed by the sample and pumped to virtual states; it then reemits photons with same or slightly higher/lower frequencies and jump back to ground state. If the frequency is same, it is a Rayleigh scattering process. If the frequency is lower, it is called stock shift; otherwise it is an anti-stock shift. The frequency changes is related to the molecular vibration, rotation, bending. Therefore, similar as IR spectroscopy, Raman can also be adopted as a powerful tool to study the molecular structures.

Refractive index measurement by Abbe Refractometer

Abbe refractometer measures a material’s refractive index through determining the critical angle αc under total internal reflection conditions.

Numerical aperture and resolution

The numerical aperture of a microscope objective is the measure of its ability to gather light and to resolve fine specimen detail while working at a fixed object (or specimen) distance. Resolution of an optical microscope is defined as the smallest distance between two points on a specimen that can still be distinguished as two separate entities.

Yellowness index measurement

Yellowness Index (YI) is a number calculated from spectrophotometric data to characterize the change in color of specimen from clear or white to yellow.