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STMicroelectronics Puts Up to 8 Dies in Multi-Chip Package

Thin BGA package with multiple memory chips significantly increases capacity and allows a mix of memory types in condensed space for ever smaller portable devices

GENEVA, April 4 /PRNewswire-FirstCall/ -- STMicroelectronics (NYSE:STM) , a leader in the application of multi-chip technology comprising both memory and MCU devices, has announced the capability to manufacture BGA (Ball Grid Array) packages just 1.6mm high that contain as many as eight stacked memory chips. The same technology is also being used to pack two memory dies into a 0.8mm thick UFBGA (Ultra thin Fine Pitch BGA). Devices produced using the new technology will help satisfy the ever-increasing demand for more memory in smaller volume, for phones, cameras, and PDAs.
ST's Multi-Chip Package (MCP) devices containing between two and four chips, often representing different types of memory such as SRAM, Flash, or DRAM, are already widely used in products such as mobile phones where space is at a premium. By literally stacking two or more chips on top of each other, the space required on the printed circuit board is the same as would be needed for a single chip - and because memory chips use many common signals, such as address and data bus lines, the number of connections between the package and the board is almost the same.

The use of discrete chips enables different types of memory -- such as NOR Flash and SRAM -- to be provided within the same footprint in the application, even when they are produced using different process technologies. Other typical combinations include NAND Flash and DRAM, or NOR Flash plus NAND Flash plus SRAM. The two-die package could combine an ASIC plus NAND Flash, or NOR Flash and SRAM.

Until now the number of chips that could sensibly be used in a multi-chip package has been limited by the thickness of the individual die -- typical applications that use MCPs are as concerned about total volume as they are about board area, and an increase in package height is often not an acceptable option. ST's new technology makes use of very thin die: just 40 microns thick. The die in the packages are supported and spaced apart from each other by 'interposers', which also have a thickness of 40 microns each.

The eight-die MCP consists of a stack of eight active memory chips and seven interposers, while the chips of the very thin two-die UFBGA device are separated by a single interposer. A key challenge has been development of the technology to process such thin wafers, which are approximately one quarter of the normal thickness. In addition, ST is using new techniques to reduce the wire bond loop height to approximately 40 microns for these devices; wire bonds are the gold wire connections from the die to the pads of the package, and the height of the wire loop above the die must be considerably lower than normal when the chips are so closely spaced.

The ability to pack a large amount of memory into a very small volume will be of particular utility in 3G mobile phones handling multimedia content, as well as in advanced PDAs and digital cameras. For example, the board area previously required for one gigabit (1Gb) of memory will now be able to accommodate one gigabyte (1GB), using a package stacking eight 1Gb dies. By using an MCP with more chips current products will in many cases easily get increased memory density in the same footprint.

About STMicroelectronics

STMicroelectronics is a global leader in developing and delivering semiconductor solutions across the spectrum of microelectronics applications. An unrivalled combination of silicon and system expertise, manufacturing strength, Intellectual Property (IP) portfolio and strategic partners positions the Company at the forefront of System-on-Chip (SoC) technology and its products play a key role in enabling today's convergence markets. The Company's shares are traded on the New York Stock Exchange, on Euronext Paris and on the Milan Stock Exchange. In 2004, the Company's net revenues were $8.76 billion and net earnings were $601 million. Further information on ST can be found at http://www.st.com/.


Source: STMicroelectronics

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