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Back End Test Flow Overview

In one of the last articles I discussed the purpose of the Back End Test, in this article I will shortly describe what are the stages of a Back End Test. A Back End Test is done on the chipe level and can have the following test stages (see also Figure 1):

  • Burn-In Test. During the Burn-In Test special data patterns are written and read at elevated temperature and internal voltage. The test will take several hours. The Burn-In is a kind of accelerated ageing and is done in order to find out the chips which will die in the early phase of their life (infant mortality).
  • Hot Test. Is a similar to the Hot Test at Wafer Level and is done at temperatures of about 70C. Due to Back End processing is possible that some of the DRAM cells on the chip will not function anymore as they did previously to the Back End processing. Therefore, the chips which have such bad cells should be found.
  • Cold Test. Is a similar to the Cold Test at Wafer Level and is done at temperatures of about -10C.
  • Speed Test. A Speed Test (how quick you can read and write the data from/in the chip) is done in order to classify the chips in different speed sorts and thus to assure that the chips that will be on one and the same module will have nearly the same speed sorts. One low speed chip on a module will make the whole module slow, in spite of the fact that maybe the other chips on the module are very fast. Also, should be taken into account that normally the chips with a higher speed are more expensive than those with a lower speed.
  • Back End Test Flow Overview
  • Figure 1: Back End test Flow Overview