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SRC to standardise 3D chip testing

Posted: 15 Apr 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Duke University? 3D chip? TSV? SRC? fab?

A large volume of 3D chips are increasingly being manufactured or are close to being manufactured by every major fab across the globe. As such, a standardised system necessary to test the devices should be set in place right. For now, makers have to settle for expensive nanoprobe systems such as the ones offered by Cascade Microtech Inc. (Beaverton, Ore.), which could be discouraging to a number of companies.

The Semiconductor Research Corp. (SRC) thinks Krishnendu "Kris" Chakrabarty, professor at Duke University, has a better idea. Chakrabarty, whose was funded to do the work, has come up with an idea that can be used on the assembly line.

"A challenge to manufacturing test has always been accessibility: how can you get inside the die to be sure you are testing for all the defects," said Chakrabarty. "This challenge is exacerbated by 3D, when access to stacked dies becomes harder." In addition, the through-silicon vias (TSVs) that connect the stacked die also need to be tested for defects. Chakrabarty and his team at Duke recognised this and have developed innovative solutions, guided by SRC's members, for testing both before and after stacking and bonding."

3D stacked chips

3D stacked chips are connected by copper through-silicon-vias terminated in microbumps. (Source: Duke University)

The technique boils down to designing-for-test the TSVs, so that large inexpensive probes can touch many TSV microbumps simultaneously to take measurements that ensure that the stacked die are defect free.

"Our design-for-testability (DFT) technique makes high volume fabs for stacked die 3D chips feasible," noted Chakrabarty.

Chakrabarty suggests that his DFT technique be used both before and after stacking and bonding the chips on every chip at first. Then as a fab becomes familiar with the results of each step and the likelihood of defects at each step, they will be able begin skipping testing steps while still keeping yields high.

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