TEST HAPPENS TWICE

Bare on the wafer, then finished in package

wafer sort, then final test

Every die is tested electrically while still on the wafer, a step called wafer sort, so bad die never waste money being packaged. After packaging, the same chip is tested again as final test, since packaging itself can introduce its own new failures.

Testing twice catches different problems: one before packaging, one because of it.

WHAT GETS TESTED

More than just 'does it turn on'

Functional test Does every circuit block actually do what it's supposed to

Parametric test How fast can it run, and at what voltage and power

Leakage test How much current does it draw when it should be idle

A chip can pass functional test and still fail on speed or power.

BINNING

One design, several products

the same chip, sold at different speeds

Manufacturing variation means chips from the very same design don't all perform identically. Binning sorts tested chips by measured speed and power into different product grades, so a single design can be sold as several different products at several different prices.

The fastest and slowest versions of a chip often started as the exact same design.

BURN-IN

Forcing early failures to happen early

stress it now, so it doesn't fail later

Some chips have a hidden weakness that fails almost immediately under stress, called infant mortality. Burn-in runs a chip at elevated temperature and voltage for a period of time before it ships, deliberately forcing that kind of early failure to happen at the factory instead of in a customer's hands.

Burn-in trades a little factory time for a lot fewer field failures.

UNIT 40 STUDY COMPLETE

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Ready for the Fab Challenge?

You've covered how a chip is tested, sorted into bins, and stressed before it ships.