The total cost of test is the overriding consideration driving changes in probing technology. Memories are not the only devices being tested; but because their pricing is so competitive, test costs must be controlled closely. Dataquest's recent DRAM cost model estimates that 16-Mb DRAM manufacturers spend about $ 1 per good device in test and packaging, but that 64-Mb DRAM manufacturers spend nearly $5. As memories get larger, they require only a few more connections, but their test time goes up linearly with density. According to Mark Brandemuehl, director of probe card marketing at FormFactor, "Probe test times for DRAMs have increased to minutes per wafer touchdown with the 64-Mb generation and will exceed 10 minutes for early 256-Mb devices. The only way to counter this trend is to test a higher number of devices per touchdown."
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