Elpida Memory Inc. said it will use the probe cards to test low-power mobile DRAMs aimed at cellular phones.

To date, the difficulty in testing bare DRAMs, compared with flash or SRAMs in unpackaged form, has limited the use of DRAMs in the stacked packages used in cell phones. That may change as probe card vendors develop wafer-level test capabilities that make it easier to fully test DRAMs in parallel and then stack them with flash in multichip packages for the 3G cell-phone market.

FormFactor (Livermore, Calif.) has become the largest probe card vendor, according to VLSI Research Inc. (San Jose, Calif.), as it applies its ceramic microspring technology to the increasingly tightly spaced pads on bare DRAM dice.

Mark Brandemuehl, vice president of marketing at FormFactor, said the company's previous line of probe cards was capable of testing DRAMs operating at 30 to 60 MHz. The new S200 series architecture has a fidelity rating — which measures the loss of signal — of 1 dB for a 200-MHz device. Crosstalk isolation, which he said is normally 5 to 10 dB, has been improved to 20 dB.

Other vendors are not sitting still. One source said Kulicke & Soffa's test division is working on a new line of probe cards that will match the capabilities of FormFactor's product.

FormFactor launched its initial public offering in June and last week reported 2003 revenue of $98.3 million, up 25 percent from 2002. In the fourth quarter of 2003, its revenue was $31 million.

Lane Mason, a memory analyst at Denali Software Inc., said the challenge of testing bare DRAM dice is one reason that few vendors offer them in unpackaged form. Micron Technology Inc. offers bare DRAM dice, but Samsung Electronics Co. Ltd. does not, he noted. And to date, most bare DRAM dice have been low-speed parts. As a result, the multichip packages normally contain flash and SRAM memories, both of which are easier to test in bare-die form, he said.

That's changing, FormFactor's Brandemuehl said, as third-generation cell phones bulk up on memory — particularly DRAM, for the application processors.

"Early in 2005 is when we believe significant volumes of DRAM will go into the advanced cell phones. Applications such as streaming video will drive up the performance requirements for the application processors, as well as the memory bandwidth needed for the memory," Brandemuehl said.

By: DocMemory
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