Price competition is a major concern for most semiconductor memory manufacturers. In the last few years, memory prices have declined dramatically, forcing manufacturers to work aggressively to reduce production costs. As memories grow in size and complexity, test time increases geometrically. As a result, testing accounts for an increasing share of the cost of memory production.
Dataquest has estimated that final test costs represent 8.5 percent of the total manufacturing cost of DRAMs. Much of this cost is directly attributable to the way memories are tested. Memory manufacturers normally rely on a multi-phase testing process in which each device is burned-in and tested to ensure that it meets the performance and reliability specifications required. During burn-in, memories are electrically and thermally stressed, typically for several hours, to accelerate failures so they can be detected during final test. This process allows manufacturers to screen out defective ICs, including those with latent defects, prior to shipment and incorporation into end products.
Final testing is traditionally performed using very expensive, high performance multi-site testing equipment. This equipment, which can cost more than $2.5 million per system, is only capable of testing up to 64 ICs at a time. Unfortunately, since only a fraction of the tests performed by these systems actually require the costly high performance features, the tester's capabilities are severely underutilized.
Massively Parallel Test Systems perform the time consuming functional tests of the traditional tester, off-loading up to 80 percent of the test time from the final tester. Massively Parallel Test Systems, such as the MTX Parallel Functional Test System, are a cost-effective solution that can test thousands of ICs simultaneously and can provide traditional burn-in as well. This allows semiconductor manufacturers to use their higher cost testers for the high speed and high accuracy tests for which they are best suited, rather than inefficiently using them for time-consuming functional tests. Using the massively parallel memory testing solution rather than traditional testing methods, high volume memory manufacturers can reduce their equipment expenditures by tens of millions of dollars.
Because it combines burn-in and functional tests, there are no additional handling steps required to realize the benefits of a massively parallel test system. Moreover, testing during burn-in detects intermittent failures that only occur during burn-in and that would otherwise pass during a traditional final test. Test results from high-accuracy massively parallel test systems correlate extremely well with those obtained using traditional memory testers.
