What’s WAT? An Overview Of WAT/PCM Data

More about the data that the fab makes available to the fabless customer when the wafer is ready to ship.


Wafer acceptance testing (WAT) also known as process control monitoring (PCM) data is data generated by the fab at the end of manufacturing and generally made available to the fabless customer for every wafer. The data will typically have between forty and one hundred tests, each test having a result for each site (or “drop-in”) on the wafer. The sites are located so that the fab can monitor the consistency of key parameters across the wafer. Within the fab itself, there is a statistical process control system which uses this (and other) data to improve yield and reduce defects.

Typically the data is sent per lot, so 25 wafers are represented in a single data file. The formats are often ASCII CSV (comma separated value) or Excel. Any modern yield management system (YMS) or yield analysis system will be able to support this type of data. Contact us for more details of what a typical file looks like.

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