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.
Availability of High Density Interconnect Flexible Circuits
Flexible circuit interconnect has been an enabling technology in a wide range of applications, including automotive, industrial, military and aerospace, computer, telecommunication, consumer, and medical products. Flexible circuit or tape automated bonding (TAB) has also been a key interconnect for IC packages. Over the last few years the industry has expanded, and growth in the high density interconnect (HDI) segment of the market promises to exceed that of the traditional material in dollar value.
Mechanical behaviour and durability of high volume fly ash cementitious composites
The purpose of this research is to separate different morphological particles of ASTM class F fly ash, and study their effect on mechanical behaviour and durability of high volume cementitious mixtures. In this research wet separation of raw fly ash is carried out, which resulted in three layers of different morphological particles. The first layer of particles float, comprise of about 1-5% of fly ash, is identified as cenospheres or hollow spheres. The second layer of particles is measured to be 55-60% of raw fly ash and consisting of porous spherical and rounded particles rich in Si and Al. The third layer particles is measured to be about 35-40% of raw fly ash. High volume fly ash cementitious composites containing second or third layer particles are tested under compression and bending, highlighting a higher strength and ductility in comparison to cementitious ones containing raw fly ash particles. KEYWORDS. Cementitious matrix; Raw fly ash; Second layer particles; Third layer particles.