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Custom dice tossed for system-in-package

Posted: 12 May 2004 ?? ?Print Version ?Bookmark and Share

Keywords:inapac technology? dram? sip?

A fabless DRAM company that has been providing product to select partners for some time, albeit in stealth mode, will take off the wraps this week. Inapac Technology Inc. is making an unusual move in offering custom, fully tested DRAM dice in system-in-package (SiP) configurations.

The startup will also assist customers with SiP development and could potentially work on a custom DRAM design specifically for SiP integration.

Inapac's self-disclosure comes at a time when consumer and telecommunications applications are increasingly turning to SiP technologies. President and CEO Jean-Pierre Braun said SiP has become the only viable answer to many system design problems.

The persistent pressure on end-system form factors demands continued integration. Yet the rapid expansion of software-based features in everything from cellular handsets to digital cameras to hearing aids is forcing systems to include more memory - often, more memory than can reasonably be implemented in SRAM, Braun said. Embedded DRAM continues to be an expensive, risky option with a long design cycle, he argued. That pretty much leaves multidie packages, in which the DRAM dice are placed beside or stacked with the system ASIC, as the remaining alternative.

But the most obvious answer of where to get the DRAM dice - namely, commodity DRAM vendors - isn't necessarily the best one for the SiP developer, Braun said.

One issue is configuration. Commodity DRAMs are designed for bulk memory applications, so they are narrow and deep. Most embedded applications require just the opposite: DRAMs that are wide - often 64- or 128 bits wide - and relatively shallow.

Similarly, commodity DRAMs come with interfaces intended for PC bulk memory, such as synchronous DRAM or the DDR1 double-data-rate interface. Those interfaces are not optimized for the carefully controlled impedances and tiny distances involved in SiPs.

A related issue is power. Commodity DRAMs are designed for an environment in which the memory is simply turned off in standby mode, so they do not have particularly impressive static energy efficiency. But DRAMs in embedded applications need to have a very low-power standby mode that retains data, just as do the SRAMs they are often replacing.

But the most serious problem, Braun said, centers on known-good dice. "Every commodity DRAM vendor has a test flow in which wafer test is a relatively simply checking and sorting operation," he said.

- Ron Wilson

EE Times

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