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Purpose of the SDRAM Back End Test

As was mentioned in the Chip Level Assembly and SDRAM Factory Schematics articles, after the chips assembly the chip is normally tested again. This test at the chip level is called the Back End Test. The main purpose of the back End Test is to find chips which are:

  • Totally not functional after the chip assembly. This means that the chip was functional after the Wafer Level Test, however due to some reasons which happened in Back End during the Chip Level Assembly the chip became not functional and has to be scraped.
  • Marginal and can fail during the Application Test. There are chips which are functioning at the room temperature, but do not function any more at slightly higher or lower temperatures. These chips are marginal and have to be found in order to avoid them to be build in a module. Such a marginal chip can kill a whole module, even if the other chips on the module are totally Ok.
  • Marginal and can early fail at the customer. The Back End Test will find our also chips which at the moment seem to work perfectly, but which degrade in time quickly and could fail immediately as the chip/module will reach the customer.
  • Do not conform to the standards. The SDRAMs are regulated by the JEDEC standard. If the chip does not fulfill the conditions of this standard, it will not work properly when the customer will try to use the chip according to the standard. Thus, such chips should be found and scraped.