Celestica

About: Celestica is a based out in . It is known for research contribution in the topics: Soldering & Printed circuit board. The organization has 186 authors who have published 214 publications receiving 2521 citations.

A new soft-switched quasi-single-stage (QSS) bi-directional inverter/charger

Abstract: A new soft-switched quasi single-stage (QSS) bidirectional inverter/charger topology is proposed in this paper. It realizes seamless four-quadrant operation in inverter mode, and rectifier operation with unity power factor in charger mode. Single stage power conversion, standard half-bridge connection of devices, soft-switching for all the power devices, low conduction loss, simple center-aligned PWM control, and high efficiency are among the salient features. The principles of circuit operation, PWM control and synthesis, and topological extension are discussed in this paper. The experimental results on a 3 kVA prototype (12 V DC to and from 110 V AC) are also presented.

Electrically conductive adhesives for surface mount solder replacement

Abstract: Electrically conductive adhesives offer a lead free, relatively low temperature process for attachment of surface mount components to printed circuit boards (PCB's). The National Center for Manufacturing Sciences (NCMS) Conductive Adhesives project has defined a requirement for an isotropically conductive adhesive (ICA). In this study, 25 commercially available silver-filled epoxies were evaluated for joint resistance stability on copper and tin/lead surface finishes after 500 h of 85/spl deg/C/85% RH aging. Mechanical properties were evaluated through lap shear and impact testing. This testing led to a set of requirements for a surface mount adhesive including a volume resistivity of 1 m/spl Omega/-cm, less than a 20% shift in resistance after aging, and the ability to pass six drops with a plastic leaded chip carrier (PLCC) 44 package from a height of 1.52 m (60 in). Promising candidate adhesives identified in the screening study were evaluated on a circuit board test vehicle with a variety of components. Assembly revealed a narrow processing window when compared to solder. Impact testing demonstrated that current materials have inadequate impact strength for many components and accelerated T/H aging reveals unstable electrical resistance with Sn/Pb finished components. Preliminary data is included on a new adhesive formulation that has been developed to address the shortcomings of currently available ICAs.

Input current ripple cancellation in synchronized, parallel connected critically continuous boost converters

Abstract: In high power factor AC-to-DC applications, boost power converters operating on the boundary of continuous mode and discontinuous mode switch with variable frequency and draw high peak input currents. A method is presented to parallel two or more of these power converters to reduce the high peak input currents. Each power converter continues to operate on the boundary of continuous mode and discontinuous mode and maintains the benefits of zero-voltage switching.

New start-up schemes for isolated full-bridge boost converters

Abstract: Two new start-up schemes for isolated full-bridge boost converters are proposed in this paper. The control timing for each scheme, which is compatible with pulse-width modulated (PWM) control timing for normal boost mode operation, are investigated. Design considerations on the relationship between the turns ratios of the boost choke windings and the main transformer windings, and its effects on the operation of the converter, are studied. The two proposed start-up schemes are experimentally verified on a 1.6 kW, 12 V/288 V prototype.

Electroless Ni/Immersion Au interconnects: Investigation of black pad in wire bonds and solder joints

Abstract: Black Pad was observed on Electroless Ni/Immersion Au (ENIG) wire bond pads. Thick immersion Au on highly corroded electroless Ni was detected. It was determined that the pads were electrically connected to the Cu ground plane due to a Ni bridge formed inside normally open photovias. The mechanism of the bridge formation was verified and preventative actions were taken; it was demonstrated that formation of Black Pad could be switched on and off. The mechanism of Black Pad formation is proposed to be defective ENIG plating involving variation of both the electroless Ni and immersion Au plating processes. The intermetallic structures of solder joints on the above pads were studied. The study was conducted on both defective and non-defective pads to show differences in intermetallic structure and composition. Me2Sn4 and Me2Sn2 (Me=Cu, Ni, and Au) intermetallics were formed on non-defective pads, which nucleated on the Ni layer and grew inside the molten solder. However, only the Me3Sn intermetallic was formed on defective pads inside the corroded Ni Layer. Both mechanisms of intermetallic formation were found on pads with mildly corroded Ni and intermediate Au thickness (4.5–7 in).