Fujitsu and Philips Test Technology for SDRAMs

In a collaboration initiated in 1997, Fujitsu and Philips jointly developed a Design-for-Test methodology to facilitate assembly interconnection testing of "complex" memory devices.

Complex memories require an initialization sequence or are accessed by a more complex protocol, and therefore complicate assembly test. Examples are Synchronous Dynamic Random Access Memory (SDRAM), Double Data Rate DRAM (DRDRAM) and Flash.

With the trend towards smaller pin pitch and chip scale packages (CSP) for memories, testing of solder connections becomes ever more complicated and expensive. The new test technology enables the user to detect all static solder connection faults (open, short, stuck@0, stuck@1) by using simple low cost testers. Diagnosis is significantly improved while test time and therefore manufacturing time can be dramatically reduced, resulting in lower production cost.

Called Static Component Interconnection Test Technology (SCITT), the concept is compatible with boundary-scan, the recognized standard for manufacturing defect testing, formulated by the international Joint Test Action Group (JTAG) and standardized as IEEE Std. 1149.1.

SCITT test technology enables memory interconnect testing to be undertaken with almost zero die size penalty, no change in device package and footprint, and no performance degradation. SCITT is based on a loop-back function incorporated in the I/O area of the memory device. The use of XNOR combinations makes it possible to run a single pass of walking-0 and walking-1 tests to detect all static connection faults. Philips estimates that this concept will reduce test time from seconds to milliseconds. The generic nature of this test technology makes it easily applicable for all memory densities and device organizations.

The concept has been proposed to the JEDEC committee and presented at the International Test Conference in Washington D.C. where memory users/suppliers as well as test equipment manufacturers showed interest in the concept. Industry-wide standardization is in consideration.

The first device supporting SCITT is Fujitsu's 64Mbit (2Mx32) SDRAM which will be available at the beginning of 1999.