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.
Flip chip assembly on organic boards using anisotropic conductive adhesives (ACAs) and nickel/gold bumps
Flip chip assembly directly on organic boards offers miniaturization of package size and reduced in interconnection distances, resulting in a high performance and cost-competitive packaging method. This paper describes the investigation of alternative low cost flip-chip mounting processes using electroless Ni/Au bumps and anisotropic conductive adhesives/films as an interconnection material on organic boards such as FR-4. As bumps for flip chip, electroless Ni/Au plating was performed and characterized for plating speed, surface roughness, and elemental analysis as a function of plating condition. High plating rate and surface planarity of the electroless Ni were considered as requirements for ACA flip chip bumps. In order to obtain high plating rate and low surface roughness, plating conditions were determined by controlling complexing agents in electroless Ni solution. Annealing effects on Ni bump characteristics showed that the formation of crystalline Ni with Ni/sub 3/P precipitation above 300/spl deg/C causes an increase in hardness and intrinsic stress, resulting in reliability limitation. As an interconnect material, modified ACFs composed of Ni conductive fillers for electrical conductor and nonconductive inorganic fillers for modification of film properties such as CTE and tensile strength were formulated for improved electrical and mechanical properties of ACF interconnection. The thermal cycle life of ACAs flip chip on organic boards was usually limited by the CTE mismatch between chip and board. However, flip chip assembly on FR-4 boards using modified ACAs almost doubled the thermal cycle life.
A New Vacuum Pressure Infiltration CFRP Method and Preparation Experimental Study of Composite
In order to prepare a carbon-fiber-reinforced polymer composite (CFRP) with ideal microstructure and properties, a new vacuum pressure infiltration CFRP method is proposed based on an analysis of existing CFRP preparation process methods. Research on composite material preparation systems was carried out by using this new method principle. The system mainly includes a fiber pre-forming module, a vacuum heating infiltration module, a hot-press curing molding module, and a data acquisition control module. Under the conditions of natural curing at 0 MPa + 6 h + 25 °C, vacuum heating curing at –0.05 MPa + 30 min + 80 °C, and hot-press curing at 0.7 MPa + 5 min + 50 °C, a two-dimensional (2D) CFRP with excellent microstructure and properties was successfully prepared. Observing the microstructure of the prepared composite material, it can be found that the inside of the composite material was sufficiently and uniformly infiltrated, and common preparation defects such as holes and delamination were effectively controlled. Through the performance test, the bending strength of the material reached 790 MPa.