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.
Curing and bonding behaviors of anisotropic conductive films (ACFs) by ultrasonic vibration for flip chip interconnection
In this study, the curing and bonding behaviors of ACFs by ultrasonic vibration for flip chip interconnection were investigated using a 40 kHz ultrasonic bonder with longitudinal vibration. In-situ temperature of the ACF layer during thermosonic (TS) bonding was measured to investigate the effects of substrate materials and substrate temperature. Curing of the ACFs by ultrasonic vibration was investigated by dynamic scanning calorimetry (DSC) analysis in comparison with isothermal cure. Die adhesion strength of TS bonded specimens was compared with that of thermo-compression (TC) bonded specimens. The temperature of the ACF layer during TS bonding was significantly affected not by substrate temperature but by substrate materials. The temperature of the ACF layer increased up to 300degC within 2 seconds on FR-4 substrates but 250 degC within 4 seconds on glass substrates at room temperature. ACFs were fully cured within 3 by ultrasonic vibration, because ACF temperature reached at 300 degC within 3 seconds. Die adhesion strengths of TS bonded specimens were as high as those of TC bonded specimens both on FR-4 and glass substrates. As a summary, TS bonding of ACF will significantly reduce the ACF bonding times at several seconds, and also make the bonding possible at room temperature compared with tens of seconds bonding times and more than 180degC bonding temperature of TC bonding
Morphology and dynamic mechanical properties of glass beads filled low density polyethylene composites
Abstract The dynamic mechanical properties of glass bead filled low density polyethylene (LDPE) composites have been investigated using a dynamic mechanical analyzer. With the addition of the glass bead volume fraction ( φ f ), the relative storage modulus and the relative loss modulus increase non-linearly at 25°C, but the damping reaction is opposite to this. The effects of the glass bead size on the dynamic modulus are insignificant except for individual data points. When the weight fraction ( φ ) of the glass beads is 10%, the values of the glass transition temperature for the composites are greatly reduced. The dynamic moduli of the filled system, for which the surface of the glass beads was pretreated with a silane coupling agent, is greater than that of the one in which the glass beads are untreated. In addition, scanning electron microscopy (SEM) has been used to study the interfacial adhesion between the inclusions and the matrix, as well as the particle distribution in the matrix.