All we care about is that our cycle time (CT) is predictable for 100% of our lots so we can accurately quote delivery times to our customers. If we are concerned about how long our lots will take to complete, we want to look at leading edge indicators to avoid delays.
Assuming we understand what our Theoretical CT is and we know that we are not within 1.5 or 2x that number; here is a tip for you.
We want to look at 2 data points for our CT, Static (SCT) and Dynamic (DCT).
SCT gives us the absolute time it takes to process a lot through any assembly line and can be looked at in individual process steps. We know manufacturing has issues on a daily basis that affects our CT such as; machine stops/breakages, non-conforming material (MRB's), lost lots, etc. All these stoppages are included in the total SCT.
DCT tells us how fast lots can move through an assembly line when all things are normal. Dynamic CT is a calculation considering line WIP and machine throughput. This is in essence line speed. The calculation is a leading indicator of what your CT will be as opposed to Static, which is a trailing data point.
DCT is my first line of defense to avoid being late on customer deliveries. Monitoring my DCT, I can see the problems coming down the line and probably do something quickly to avoid having late lots. Looking at SCT alone will merely tell me history and offers no way to change the outcome.
Depending on how fast we fix relative issues on the line we would expect that DCT and SCT would intersect at some point in time, once issues on the floor are resolved and the line normalizes.
To me, it is as simple as breaking the problems down into smaller issues that can be accurately categorized and fixed during the processing, not after the lot is processed. This is real time correction to problems in the line and I use to DCT to alert me. If I see the DCT increasing on a daily monitor it is a good point to ask why and help put the problem to bed before it affects customer delivery.
I have read numerous articles talking about a myriad of ways to look at reducing assembly cycle times in semiconductor manufacturing. Using SCT and DCT have allowed me to achieve world class cycle times in past lives.
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