One of the benefits of tracking equipment utilization is the ability to schedule preventative maintenance based upon actual performance. The primary function of Preventative Maintenance in the InSite | Semiconductor TAP Edition is to accurately determine when a PM is required. Based on the type of tool, limits can be set for a warning to be issued to the operator that a PM is needed and a stoppage limit can be defined such that the tool will actually be shut down. A tool is not required to use Preventative Maintenance limits at all, but could use any or all of the methods discussed below.

Methods of determining when a PM is due
In the InSite | Semiconductor TAP Edition there are three ways to determine when equipment is in need of maintenance: the number of units processed, the number of runs, and the elapsed time since the latest Preventative Maintenance.

Unit Based PM
Each time a lot is tracked out of a piece of equipment, the processed unit count is captured. This count is added to the unit count for the tool and compared to the Unit Count limit for that tool type. Typical machines that use unit-based limits are wire bonders, die attach devices, and wafer saws.

Run Based PM
Each Track-In followed by a Track-Out on a tool is considered one ‘run’. A count of each run is made and compared to the Run Count limit for that tool type. Equipment that is run-based includes burn-in ovens, curing ovens, and plating and wash units. This is due to the fact that the number of units in the run is not as important as the number of times the unit is heated up, loaded with chemicals, etc.

Time Based PM
Finally, some equipment needs to undergo preventative maintenance on a regular cycle whether or not it is processing runs. The elapsed hours since the latest PM are counted each time the equipment is set up, or is used for tracking lots in or out. If the hours exceed the PM time limit, a PM warning or shutdown is initiated. Typical examples of time-based equipment are a device that is never shut down or one that is run so often that the preventative maintenance cycle is very predictable.

Activities Accomplished at a Preventative Maintenance Event
When a tool undergoes preventative maintenance it is automatically shut down and unavailable for production use until the PM is complete. The unit count and the run count for that resource are reset to zero and a time-stamp is made of when the PM is complete. This time will be the basis for measuring the time when using Time Based PM limits (current time – PM time = time since last PM). Once the PM is complete, the equipment is brought back online and made available for production.