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Development of Organic Multi Chip Package for high performance application
Keywords: Organic Interposer, 2.5D, Package
In recent years, the conventional FC-BGA (Flip Chip Ball Grid Array) substrate manufacturing method (Electro-less Cu plating, Desmear, Laser Drilling processing) is becoming the limit of miniaturization of wiring and narrow pitch of flip chip pad. On the other hand, Semiconductor is considered miniaturization and higher density flip chip pad and goes further in the future. Therefore we have been developing Organic Multi Chip Package, having a multi-chip and corresponding to a narrow pitch and the function of the interposer. Feature of Organic Multi Chip Package is that without the glass and Si Interposer, fine wiring layer is formed directly on the PWB(Printed Wire Board)package, using a thin film process. More specifically, the processing is performed including a small diameter via with an insulating resin technology smoothed by CMP(Chemical Mechanical Polishing ), sputtered seed layer, and photosensitive resin. Top layer to form a Cu pad is treated by OSP(Organic Solderability Preservative). The back side of BGA is the SR layer similar to a typical FC-BGA. The following is the structure of the prototype Organic Multi Chip Package. The part of PWB Core consists of 2 layers, which has φ100um diameter through-holes. And the build-up of the chip-side is composed of 2layers the build up of BGA side is composed of 3layers and solder resist. Therefore, the structure is asymmetric. And then design of thin film layer is, over 40mmx40mm square package size, 10um via diameter can be formed with 40um pad pitch, and then Cu pad diameter becomes 25um. Forming 3 wiring layers, Cu trace can be very fine up to L/S=2/2um and 2.5um thickness. From these results, Organic Multi Chip Package can be easily done to the pitch conversion from the chip to the board. The warpage of Organic Multi Chip Package can be reduced in the optimization of structure and materials. Therefore, we were possible to connect the chip to chip through the fine wiring of the surface layer. For example, multi-chip assembly of high pin count logic and, standardized Wide I/O memories are enabled. We think that there are some advantages in the structure of the Organic Multi Chip Package. The first one is total height. With the Si interposer, there is the height of the solder joint between the PWB substrate and interposer, and also the height of the Si interposer. However, Organic Multi Chip Package will enable direct assembly of the chip, so the total height can be lower than the assembled glass and Si interposer. Secondly, process is simple compared with current 2.5D which is necessary to assemble the interposer to substrate, and chip to interposer. But, Organic Multi Chip Package has interposer function in it. Finally, fine line formation on Organic Multi Chip Package has been successfully processed. Reliability test is progressing now. We will discuss process of Organic Multi Chip Package and the result of reliability test in this paper.
Noriyoshi Shimizu,
Nagano-shi, Nagano

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