Wright Williams & Kelly
Factory Explorer® v2.2 Technical Alert #6
Summary: When simulating models that contain alternative process steps, Factory Explorer® can generate incorrect cycle time contribution estimates. This error affects not only tools listed on alternative process steps, but other tools in the model. This error is corrected in Factory Explorer® v2.2a, and Factory Explorer® v2.3 beta 4.
Details: To estimate cycle time contribution by tool group, Factory Explorer® maintains a list of tool-visit information for each active lot. When a lot completes processing in the factory, this visit information is unrolled and recorded at the tool group level. Upon completion of the simulation, Factory Explorer® uses this accumulated visit information to estimate overall cycle time contribution by tool group. In models containing alternative process steps, tool-visit information at the lot level can become corrupted, due to the way lots are created and destroyed at alternative process steps. This corruption can affect tools that are not used at alternative process steps. The exact impact of this corruption is hard to predict in advance, but can result in sizable errors in the estimated number of visits, and overall cycle time contribution.
Workaround: WWK is currently beta-testing an intermediate release, Factory Explorer® v2.2a, that fixes this error. This intermediate release will be distributed to all maintenance contract customers within 1-2 weeks.