Focus: Processor makers' flippin' genius

The next generation of chip packaging will mean simpler, cheaper PCs for consumers
Written by Matthew Broersma, Contributor

When Advanced Micro Devices (AMD) in the next few weeks introduces its new Duron microprocessor, the chip will be faster and cheaper partly because of a prosaic-sounding technology called flip-chip pin grid array packaging. But FCPGA, as it's known in the trade, is part of a trend experts believe will ultimately lead to less expensive, simpler-to-use PCs for consumers.

Broadly, FCPGA makes use of two innovations: a smaller, cheaper-to-manufacture package and a more efficient heat-removal system.

Older chips, such as Intel's Pentium II or the current family of AMD's Athlons, reside in a "slot" package, which encases the processor and the L2 cache in a rectangular case. (The L2 cache stores frequently-used information, and the speed at which it can be accessed is crucial to overall system performance.) The recent advent of new manufacturing processes, however, has meant the L2 cache can be brought directly onto the processor die, eliminating the need for the slot package.

Instead, the chip, with its on-die L2 cache, could be mounted in socket packaging, with its pins on the bottom -- the "pin grid array". Socket packages are much cheaper to manufacture than the bulky slot package: industry analysts estimate switching to socketed design will save AMD $10-$15 (£6.4-£9.6) on every part.

In addition to the decreased manufacturing price, which makes cheaper overall systems possible, the next generation of socketed chips is significantly faster than the slot design.

In older chips the access speed for the L2 cache -- the backside bus speed -- could only reach half that of the chip speed, so an 800MHz chip would have a backside bus running at 400MHz. That limitation goes away with socketed parts, allowing, for example, Intel's new 1GHz Pentium III to access the L2 cache at 1GHz. While superior to the Pentium III in some ways, AMD's 1GHz Athlon is still limited to a 500MHz backside bus speed.

The "flip-chip" part of the package has to do primarily with heat dissipation.

On older socket designs, the silicon resided on the bottom of the device, and heat had to make its way through the ceramic material before it could be dissipated. The newer design puts the silicon on top, allowing a direct connection to the heat sink. Increased heat dissipation allows processors to run at faster speeds without overheating.

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