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
A novel flip chip technology using non-conductive resin sheet
A novel flip chip packaging technology using non-conductive resin sheet has been studied. The process flow of this new packaging system is as follows. First, epoxy base resin sheet is laminated onto substrate to cover the substrate surface including land electrodes. Bumped chip alignment and attachment has done through the resin sheet, in the second stage with pressure and temperature. The bumps under the chip penetrate with removing resin sheet material and eventually reaching to the metal land of the substrate in this process. Metal connection and curing of the interface resin have completed in the third stage. This new process has big potential to make flip chip package simple compared with current flip chip packaging process using liquid resin with dispensing system. The through put time can be reduced to less than 10 seconds/units in actual model case even large flip chip package which has over 15/spl times/15 (mm) square area IC chip. The other advantages are thermal stability of material in the process, moisture related performance, and warpage control performance. For current underfill process we have only choice to use anhydride type resin system which has many disadvantaged on that. This new process made it possible to introduce moisture and thermally stable epoxy resin with phenol curing system for flip chip packaging. Drastic process ability improvement can be achieved by the new process and material. As a typical improvement of thermal shock performance, it was confirmed that the life of chip damage becomes over 10 times longer by flip chip bonding parameters which can be controlled only by this new flip chip packaging process.
Comparison between Two Chemicals for Reducing Scale Formation in Reverse Osmosis Systems
In this present research was transacted with the calcium carbonate scale inhibition on the membrane surface of the reverse osmosis desalination system. Influence of changing feed solution flow rate (10-25)l/h, pH of the feed solution (6-10) on the recovery ,penetrate flow rate and total dissolved solid in (RO) system by using solution of calcium carbonate as feed solution was investigated, furthermore the effect of adding two types of scale inhibitor ,zinc chloride and polyamino polyether methylene phosphonate with difference concentration (2-8)mg/l for zinc chloride and (8-15) mg/l for polyamino polyether methylene phosphonate was calculated. The results showed that the permeate rate increases as the feed flow rate augmentation ,while it reducing with time, the total dissolved solids decreases as the feed flow rate increases while it increases with time and recovery rate decreases as the feed flow rate increases and it also decreases with time. It was concluded that the permeate rate decreases as the feed solution pH value increases and it cause high scale forming thus decrease the permeate TDS.By adding the scale inhibitor, it was found that the permeate rate and recovery rates increases as the concentration of inhibitor increases while the total dissolved solids decreases in the permeate with increasing the concentration of both inhibitors .It was discovered that Polyamino polyether methylene phosphonate more sturdy than zinc chloride as scale inhibitor for reverse osmosis desalination system in all concentrations was studied in this article.