Simultaneous Chip-Join and Underfill Assembly Technology for Flip-Chip Packaging
Controlled Collapse Chip Connection (C4) flip-chip packaging is the current state of the art assembly technique. The C4 Organic Land Grid Array (OLGA) technology process to attach a silicon die to a package substrate involves seven process steps. In the current plan of record (POR) C4 OLGA flip-chip assembly process, solder wetability is achieved by removing Pb/Sn oxide films from the bump material by means of a flux and deflux process. An epoxy material is placed between the die and package. This underfill (UF) process has a long epoxy application step and curing time. We present a three-step chip-join assembly process using a no-flow-type underfill material combined with nonlead-containing bump metal on the chip side. This process has fewer process steps than the POR assembly process, and the underfill cure time is also reduced. The process described in this paper shortens the assembly process by eliminating fluxing, defluxing, and furnace reflow steps. We achieved more than a 90% assembly yield as a result of process parameter and material property optimization. INTRODUCTION Intel successfully introduced C4 OLGA technology into the Personal Computer (PC) market in April 1998. The technology has many advantages over wire bonding and Tape Automated Bonding (TAB): it has a higher Input/Output (I/O) number, shorter interconnects, and the silicon die self-aligns to the package. The current C4 OLGA plan of record (POR) process to attach a silicon die to a package substrate and apply the underfill material requires seven processing steps. An epoxy-type material is required in C4 packaging to prevent solder bumps on the silicon die from moving and electrically shorting during the life of the part. The underfill also mediates the thermal miss-match between the silicon die and the organic polymer package. The underfill material is applied in a liquid form to flow between the silicon C4 bumps and the package substrate. A high-temperature oven cure is required to set the polymer. Several different underfill formulations and bump metals were examined. We found a correlation between the size of particles in the underfill material and silicon bump to package substrate joint reliability. Different underfill resins were tested. Resins causing a higher viscosity showed better reliability after a temperature cycle reliability test. We examined the potential package assembly cost savings using our three-step process. By eliminating process steps and shortening the cure time, a substantial cost savings can be realized. This paper describes an assembly technology that targets future-generation C4 flip-chip packaging. We report a method to combine silicon chip join and epoxy underfill processes in one step with a shorter underfill cure time. The process has fewer steps than the POR assembly process. The POR assembly is shown in Figure 1 with our new assembly process flow shown in Figure 2. Intel Technology Journal Q3, 2000 Simultaneous Chip-Join and Underfill Assembly Technology for Flip-Chip Packaging 2 Figure 1: Current (P856) chip join assembly process Figure 2: New one-step chip join assembly process MATERIALS AND PROCESS Materials Die Test die were used with different bump metal material. To obtain good adhesion between the bump material and die, a Ti/Au under bump metallurgy was used. Substrate The test substrate was an OLGA material with Sn/3.5Ag eutectic pre-solder paste. UF Material The no-flow-type underfill material provided by Nitto Denko was used in the testing. The UF properties of the first formulation are listed in Table 1[1]. Table 1: No-flow-type UF property
Role of feed protocol in achieving chaotic mixing of highly filled flow systems during filling the empty cavity
Title of Dissertation: ROLE OF FEED PROTOCOL IN ACHIEVING CHAOTIC MIXING OF HIGHLY FILLED FLOW SYSTEMS DURING FILLING THE EMPTY CAVITY Yue Huang, Doctor of Philosophy, 2006 Dissertation directed by: Professor David Bigio Department of Mechanical Engineering Chaotic mixing of highly filled viscous fluids is desired but hardly achieved in the electronic packaging industries. The demand for high reliability found in electronic package attracts more and more researchers to study the properties and distribution of binders and filler particles. These will affect properties such as coefficient of thermal expansion and stiffness. Both of these contribute strongly to reliability. The filler concentration, size distribution and spatial distribution must be examined in a structured manner to understand their effects on final properties. However, most studies deal with filler concentration and size distribution, while very few studies have tied the particle spatial distribution to the properties. It is not enough to just properly control the filler concentration and size distribution. The more uniform filler distribution, the more uniform are local properties, and this can be achieved by well-designed mixing processes. Mixing is very important and in many cases the goodness of the mixing of fillers will affect or determine the properties of the products. In this thesis, the local properties of electronic package and their relations with filler particle distribution are quantified. For the first time, a new feed protocol that can generate chaotic mixing during filling cavity by implementing periodic and aperiodic filling process is presented. Instead of using single gate in the molding process, we have developed a two-gate feeding protocol. A numerical simulation experiment is conducted on a 2-D square cavity to examine the mixing of polymer fluid in low Reynolds number flows. Since there are a vast number of geometries in electronic packages, only cavities with 46 and 49 bumps, which can be treated as solder balls or leadframe, is investigated. Periodic and aperiodic feed protocols resulted in exponential growth of the distance between two adjacent particles, an indication of chaotic mixing. Entropic study shows that the global mixing has been improved 858% compared to single gate feeding. The improved properties and reliability could be foreseen in electronic package. ROLE OF FEED PROTOCOL IN ACHIEVING CHAOTIC MIXING OF HIGHLY FILLED FLOW SYSTEMS DURING FILLING THE EMPTY CAVITY
Computer-Aided System of Virtual Testing of Gas Turbine Engines
The article describes the concept of a virtual lab that includes subsystem of gas turbine engine simulation, subsystem of experiment planning, subsystem of measurement errors simulation, subsystem of simulator identification and others. The basis for virtual lab development is the computer-aided system of thermogasdynamic research and analysis “ASTRA”. The features of gas turbine engine transient modes simulator are described. The principal difference between the simulators of transient and stationary modes of gas turbine engines is that the energy balance of the compressor and turbine becomes not applicable. The computer-aided system of virtual gas turbine engine testing was created using the developed transient modes simulator. This system solves the tasks of operational (throttling, speed, climatic, altitude) characteristics calculation, analysis of transient dynamics and selection of optimal control laws. Besides, the system of virtual gas turbine engine testing is a clear demonstration of gas turbine engine working process and the regularities of engine elements collaboration. The interface of the system of virtual gas turbine engine testing is described in the article and some screenshots of the interface elements are provided. The developed system of virtual gas turbine engine testing provides means for reducing the laboriousness of gas turbine engines testing. Besides, the implementation of this system in the learning process allows the diversification of lab works and therefore improve the quality of training.