New liquid crystal polymer (LCP) flex circuits to meet demanding reliability and end-use applications requirements
Flex circuits made from LCP, a thermoplastic polyester, use a newly developed, adhesiveless, roll-to-roll process flow similar to that used for polyimide substrate, including vacuum metallization, additive plating and chemical etching of dielectric. Critical dimensions for both LCP raw test circuits and LCP-coverlayer-laminated LCP test circuits from multiple lots met the specification established for polyimide circuits. LCP circuits have also proven to be dimensionally stable at elevated temperature in common post-circuit operations including die attachment, wire bonding, encapsulation and solder reflow. Trace adhesion was not degraded after solder immersion at 280°C. Wire bonding has proven to be as straightforward as on polyimide, yielding strong wire bonds in a large process window. Integration studies with other materials such as LCP coverlayers and soldermasks that could enable a wide variety of product constructions with multiple materials are going forward. Initial parts passed the entire battery of reliability tests that included moisture resistance, thermal shock and temp-humidity-bias stressing to enable the definition of preliminary process conditions for a wide variety of soldermasks with different polymer chemistries. LCP-based flex circuits should have extended applications beyond those for existing polyimide offerings, due to their reduced moisture uptake and coefficient of humidity expansion and better electrical properties, particularly dissipation factor. These applications include liquid crystal display module (LCDM), medical, high frequency applications, high-density disk drive and integrated circuit packaging.
Polymer integration for packaging of implantable sensors
Abstract Inexpensive, easy-to-process, light-weight polymer-based materials that are biocompatible, mechanically flexible, and optically transparent have emerged as alternatives to metals and ceramics in the packaging of implantable sensors. These materials have been used to package components such as microelectrode arrays, telemetric coils and structural membranes. Polymers are also being used for the encapsulations and coatings of the implants. The devices and packages require fine-pitch, low-loss, and highly-conductive paths on mechanically and chemically reliable polymer films. In this review, several polymers used for implantation and related integration technologies are identified. We give an overview of novel applications of polymers in implantable sensor packages, and identify future directions for their application. Polymers exhibit high moisture absorption rate, high-frequency electrical loss, and low mechanical stability. These properties are aggravated when polymers are used for in vivo applications. Also, the integration of polymers with polymers/metals at high bonding temperatures and pressures may degrade their properties and interfaces. Furthermore, adhesive bonding and physical/chemical deposition methods for the integration may introduce non-hermetic, permeable, optically opaque, and poorly conductive interfaces. Thus, creating polymer-based high-density and small-dimension structures are critical for packaging. To address these issues, polymers with improved characteristics as well as integration techniques using low bonding temperature and pressure are indispensable. Liquid crystal polymer (LCP) and surface activated bonding (SAB) technologies meet these requirements. SAB technologies enable nanoscaled polymer–polymer/metal bonding to realize reliable, miniaturized, and high-performance packages for implantable sensors. This article is meant to serve as a reference for future research in the emerging field of implantable sensors by critically assessing the specific merits and drawbacks of several material-process combinations.
The structure of electricity demand in the Brazilian household sector
Abstract The present structure of residential electricity demand is analysed by electricity consumption classes and end-uses. Nearly 70% of households consume less than 150 kWh/month and are responsible for 35% of total residential demand. Other determinants of electricity-use, such as income and place of residence, are also discussed. It is found that electricity demand is increasing faster than income as the country reaches appliances saturation in upper consumption levels. Water heating and refrigeration account for the major part of residential consumption. Residential conservation efforts have started introducing more efficient lighting equipment and refrigerators, but further work will have to be done to speed up the diffusion of efficient technology at costs that can be paid by consumers.