Authors: Hiroki Tanaka, Company: Hitachi Cable Ltd. Date Published: 9/10/1996
Surface Mount International
Abstract: In the recent trends of increasing LSI’S 1/0 count and clock speed, the developments and practical applications of Ball Grid Array (BGA) are becoming more active instead of Quad Flat Package (QFP) which has been a mainstream of high pin count LSI packages. Currently, Plastic BGA (PBGA) is taking a leading part in that activities, but it is expected that Tape BGA @GA) using TAB tape as an interposer will take more important position as a technology to realize higher 1/0 count and smaller size package in low cost because of its ability in higher circuit density compared with printed circuit board (PCB) which is used as the interposer in PBGA and in freer pitch bonding than wire bonding. In addition, the clock frequency of LSIS including microprocessor is increasing remarkably year by year, so that the electrical performance is becoming more important factor in designing and manufacturing LSI packages. It is considered that TBGA is also advantageous for high speed devices because of the shrinkage of wiring length due to its higher circuit density. On the other hand, two metal layer TAB tape having signal/power layer and ground plane layer on the both side of dielectric film, which can achieve more excellent electrical properties, is strongly required for high performance TBGA package. Fig.1 shows the examples of one and two metal TBGA package structures. In this figure, the interconnection of chip and tape leads, that is inner lead bonding (LB), is illustrated as a conventional TAB bonding using gold bumps on chip and beam leads on tape, but other LB technologies such as flip chip bonding (C4) and wire bonding technology are also possible to apply in TBGA packaging  . In designing and manufacturing two metal TAB tape, it must be considered that the ground vias which connect the ground electrodes of chip and the ground plane of tape electrically should be placed on the area close by the chip as much as possible, where the circuit density is usually highest in the fan-out wiring design on the tape, so it is essential to minimize the size of conductive vias to realize two metal TAB tape having higher circuit density. Further, high reliable metallizing technology for conductive vias and other various requirements in TBGA packaging and assembly process different from attach or solder reflow important. To meet those demands, mounting on PCB are also we have studied on an advanced process for two metal layer TAB tape manufacturing. In this paper, the outline of the results including new laser technology for via formation and new copper plating method for via metallizing ,we described.