Effects of Sintering Process Conditions on Size Shrinkages of Low-Temperature Co-Fired Ceramic Substrate

The effects of sintering process conditions on the size shrinkages of low-temperature co-fired ceramic (LTCC) substrate were investigated. The process variables investigated were thickness of the stacked raw tapes, lamination pressure, lamination-pressure holding time, pre-heating time, debinding time, sintering dwell time, and sintering temperature ramp. Results revealed that the size shrinkage percentage of the LTCC samples in the lateral directions was always smaller than that in the thickness direction. The lateral shrinkage deviations were less than 2.1% for all the experiments conducted in this study. Pre-heating time, lamination-pressure holding time, debinding time, sintering dwell time and sintering temperature ramp had almost no effects on the lateral size shrinkage of the LTCC samples, and the average of the lateral shrinkage values was 15.3%, with a standard deviation of 0.17%. Lamination pressure and stacked raw-tape thickness had effects on the lateral size shrinkage of the LTCC samples, and empirical equations for calculation of the size shrinkage values were obtained by curve fitting.     

Effects of Four Key Process Variables on Size Shrinkages of Low Temperature Co-Fired Ceramic Substrates

The effects of four key process variables on the size shrinkages of low temperature co-fired ceramic substrates were investigated using the methods of design of experiments (DOE), analysis of variance (ANOVA), and multivariable regression. The process variables investigated were raw tape thickness, laminating pressure, coining pressure, and coining time. The results revealed that coining pressure had the most significant effect on the size shrinkages of the low temperature co-fired ceramic samples under the process conditions set in this study. The average lateral size shrinkage and thickness shrinkage of the LTCC samples produced with a coining pressure of 320 MPa were significantly lower and higher than those produced with a coining pressure of 50 MPa with shrinkage differences of 3.6% and 6.2%, respectively. The effects of tape thickness, the interaction of tape thickness, laminating pressure, and coining pressure, the interaction of tape thickness and coining pressure, and the interaction of tape thickness and laminating pressure were also significant. Two regression equations were obtained and the shrinkage values could be estimated using them. The coefficients of determination R² were 99.9% and 98.9%, respectively, and the P values were smaller than 0.001 for the two regression equations. This can allow engineers to calculate the dimensions especially lateral dimensions and features such as pad pitches at the design stage and to set the process parameters at the manufacturing stage.     

Redox Mapping of Biological Samples Using EPR Imaging

Under normal conditions, cells meticulously maintain redox homeostasis. However, under abnormal conditions, such as stress, the redox equilibrium is disturbed, leading to a threat to the cellular wellbeing. Techniques that are capable of measurement of the redox status might prove useful in the detection and treatment of adverse conditions that change the cellular redox equilibrium. Electron paramagnetic resonance (EPR) imaging is a unique non-invasive imaging technique that is capable of redox measurements in vivo. EPR utilizes redox-sensitive spin labels, nitroxides. These EPR-active probes are reduced by cellular reducing agents to EPR-inactive species (hydroxylamines). The rate of reduction, among various factors, depends on the redox status of the cell, thus providing information about the redox environment of the region of interest. This review focuses on the principle, method, and application of redox mapping to biological systems.     

Real-time calculation and visualization of spectra in field-cycled dynamic nuclear polarization spectroscopy

Field-cycled dynamic nuclear polarization (FC-DNP), which is based on the Overhauser effect, provides a new way to perform in vivo measurements of free radicals in biological systems. Since it measures the alterations of the nuclear magnetic resonance (NMR) signal in the presence of paramagnetic molecules, a customized program is usually needed in FC-DNP experiments to extract spectral information from the acquired NMR signals. While this program can be designed to calculate the spectrum after all the NMR signals are collected, the batch-processing mode inevitably causes delay and is not convenient for in vivo applications. In this paper, we report the development of a real-time DNP spectrum calculation and visualization program, called RT_DNP, for FC-DNP experiments. A dynamic data exchange (DDE) client was implemented to enable real-time receipt of the system information and the NMR signals from a commercial NMR console. The received NMR signals and experimental parameters were then used to calculate the DNP spectrum during the data acquisition. The real-time DNP spectrum calculation and visualization program was tested in experiments. A seamless integration of the program into a commercial NMR console has been achieved.     

Effects of process conditions on reliability, microstructure evolution and failure modes of SnAgCu solder joints

In this study, microstructure evolution at intermetallic interfaces in SnAgCu solder joints of an area array component was investigated at various stages of a thermal cycling test. Failure modes of solder joints were analyzed to determine the effects of process conditions on crack propagation. Lead-free printed-circuit-board (PCB) assemblies were carried out using different foot print designs on PCBs, solder paste deposition volume and reflow profiles. Lead-free SnAgCu plastic-ball-grid-array (PBGA) components were assembled onto PCBs using SnAgCu solder paste. The assembled boards were subjected to the thermal cycling test (−40 °C/+125 °C), and crack initiation and crack propagation during the test were studied. Microstructure analysis and measurements of interface intermetallic growth were conducted using samples after 0, 1000, 2000 and 3000 thermal cycles. Failures were not found before 5700 thermal cycles and the characteristic lives of all solder joints produced using different process and design parameters were more than 7200 thermal cycles, indicating robust solder joints produced with a wide process window. In addition, the intermetallic interfaces were found to have Sn–Ni–Cu. The solder joints consisted of two Ag–Sn compounds exhibiting unique structures of Sn-rich and Ag-rich compounds. A crystalline star-shaped structure of Sn–Ni–Cu–P was also observed in a solder joint. The intermetallic thicknesses were less than 3 μm. The intermetallics growth was about 10% after 3000 thermal cycles. However, these compounds did not affect the reliability of the solder joints. Furthermore, findings in this study were compared with those in previous studies, and the comparison proved the validity of this study.     

Effects of Key Process Conditions on Warpage and Via Protrusion of LTCC Substrate

The effects of key process conditions on the protrusion of via conductors and warpage of low temperature co-fired ceramic (LTCC) substrates were investigated using the design of experiments and analysis of variance. The results revealed that tape thickness, via size and coining pressure had highly significant effects and the interaction of via size and coining pressure had a significant effect on the via protrusion heights of the LTCC samples. A combination of via size of 0.12 mm, raw tape thickness of 0.254 mm and coining pressure of 50 MPa produced minimized protrusion. Tape thickness, coining pressure and the interaction of them had highly significant effects on the warpage of the LTCC samples. A combination of tape thickness of 0.127 mm and coining pressure of 50 MPa produced minimized warpage. A combination of the factor settings was also recommended for obtaining low heights of both protrusion and warpage.     

Magnetic Force Microscopy of an Oxygen-Sensing Spin-Probe

In the present work we provide magnetic force microscopy (MFM) analysis on particles of a paramagnetic spin-probe lithium octa-n-butoxy-naphthalo-cyanine (LiNc-BuO) used for EPR oximetry. We demonstrate how MFM can generate a magnetic contrast in ambient air for LiNc-BuO particles when they assemble into structures >50 nm in size. The same sample when assembled into particles <10 nm in size failed to show contrast in MFM images. The potential for utilizing MFM to understand the magnetic signature of paramagnetic nanoparticles in biological samples is discussed.     

Mapping of Oxygen Concentration in Biological Samples Using EPR Imaging

Electron paramagnetic resonance (EPR) spectroscopy is widely used for measurement and imaging of oxygen and free radicals in biological systems. EPR oximetry is non-invasive, capable of providing local, reproducible, and repetitive measurements of oxygen concentration or partial pressure of oxygen (pO₂) in tissues. Although EPR oximetry is used primarily as a research tool, it has the potential to be useful in the clinic. This review provides a brief overview of the technique and its application to selected biological systems.     

A comparison of a 30-cluster survey method used in India and a purposive method in the estimation of immunization coverages in Tamil Nadu

The reaction mechanisms of p-nitrophenyl phosphate hydrolysis catalyzed by two rat liver isoenzymes of the low M(r) phosphotyrosine protein phosphatase (AcP1 and AcP2) were compared. Furthermore, the effect of some heterocyclic compounds on their activities were tested. Cyclic GMP and guanosine causes a particularly high activation of the isoenzyme AcP2, whereas its effect on AcP1 is very poor. A study on the mechanism of cyclic GMP activation was carried out. The results suggest that cyclic GMP activates the AcP2 isoenzyme by increasing the rate of the step that leads to the hydrolysis of the covalent enzyme-substrate phosphorylated complex formed during the catalytic process. The physiological significance of cyclic GMP activation of only one of the two isoenzymes (AcP2) remains uncertain.