Recent advances in anisotropic conductive adhesives (ACAs) materials and processing technology
This paper deals with three recent advances in the area of ACA materials and processing technologies, (1) wafer-level ACA, (2) ultrasonic ACA bonding, and (3) Solder ACAs. Patented idea of Wafer level package (WLP) ACA/NCA was introduced earlier as one of the promising ACA packaging technologies due to its advantages such as fewer processing steps, lower cost, and enhanced device performance compared to conventional single chip ACA packaging. WLP ACA can be widely used for flat panel display (FPD), general semiconductor packaging, and 3D-TSV applications because of cost and performance advantages. In addition, another patented novel anisotropic conductive film (ACF) bonding process using vertical ultrasonic vibration was also introduced in flex-on-board (FOB) and Touch Screen Panel(TSP) applications. The ACF temperature was precisely controlled by adjusting both U/S power and bonding pressure. The significant meaning of this technique are (1) significantly reduced ACF bonding time typically 1/3 ∼ 1/5 of conventional T/C bonding times in FOB applications, (2) less thermal damages especially for TSP assembly, and (3) compact and energy saving machine. Lastly, newly developed solder ACFs combined with Ultrasonic processing can increase twice the current handling capability of conventional Ni ACFs and show excellent reliability performance in FOB applications because of metallurgical bonding at the joint rather than physical contact of conventional ACAs.
Wafer-applied underfill: flip-chip assembly and reliability
Manufacturers of consumer electronic products are continuously striving to confer greater functionality to smaller, lighter, and less expensive packages, and flip-chip is an important enabling technology for these product trends. Underfill between the die and an organic substrate is necessary to compensate for the coefficient of thermal expansion mismatch. The underfill dispense and cure step is not a typical process for a surface-mount technology (SMT) factory, and demands additional capital equipment, floor space, cycle time, and headcount. An alternate approach to traditional capillary underfill is wafer-applied underfill. The underfill is applied after wafer bumping and sawing, but prior to the picking of the individual die from the saw tape. This paper describes the coating and assembly processes. Liquid-to-liquid thermal cycle shock tests (-55 to +125/spl deg/C) have been performed on test vehicles assembled with the wafer-applied underfill. First failures were at over 1000 cycles. Weibull plots of the data and failure analysis are presented.
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.