Bottlenecks, part 1

Almost 15 years ago I had the opportunity to attend a 4 day seminar with the authors of the well known book “Factory Physics” LINK

In the opening session we talked about what is limiting factory performance and sure enough bottlenecks came up. The question was asked , what can be done to improve a bottleneck. After a lively discussion between all attendees about what they have done or what they think should be done, Dr. Mark Spearman stated:

“… I propose you walk on the factory floor and look at the tool or tool group and see if it is indeed running (at full speed and efficiency) …”

I had a pretty big “aha !” moment and I remember this, like it was yesterday. But this proposal comes with another interesting challenge:

How do we know what is the factory bottleneck ???

I think to answer this question correctly is the foundation for a lot of things. In its simplest form, the correct answer would lead the folks who actually want to see the bottleneck on the floor to walk to the right tool/tool group. Obviously, there is much more connected to that, for example:

  • where to spend resources for improvement activities
  • if the bottleneck capacity is used to define the overall FAB capacity, it would be great, if the correct tool/tool group was identified
  • where to spend capital to buy another tool

How do we find out, what is the factory bottleneck tool group ? One obvious answer is lets look into data – what data – and how do we know it is indeed the bottleneck. The answer becomes quickly ” … it depends …”

It depends on what is the definition metric and I have seen a few of them so far:

  • highest tool utilization as per capacity planning numbers
  • highest tool utilization as per actual numbers (daily, last week , 4 weeks ?)
  • highest amount of WIP behind tool group
  • highest average lot wait time at the tool group
  • highest miss of daily moves vs. target
  • frequency / intensity a tool group is discussed in morning meeting as a “problem kid”
  • lowest tool group uptime ( or availability)
  • highest OEE value

I’m pretty sure all of these metrics have some value, if used in the right context. I do have my own opinion, what I would select as the key metric, to declare the FAB bottleneck, but I really like to get some discussion going here, therefore I like to run a little poll, to see what the majority would select as the key metric:

I can’t wait to see the results. I’m fully aware that the answer selection is not that straightforward without more content – so if you like to provide thoughts, please use the comment functionally at the bottom.

I will share and discuss the results in my next post, sometime before the holidays


6 thoughts on “Bottlenecks, part 1

  1. Hi Thomas. You will probably agree that I am not the most qualified to leave a vote in here. I find your poll a good start, especially since I am planning to propose the specification of a dashboard for bottleneck management into our MES.
    What I noticed in your options is that some may be pointing to a well managed bottleneck while others may to a badly managed one. Furthermore there is planned versus unplanned bottleneck. For each of these, there would probably be a different option suitable. Being an IT person, I tend to the ones relying on data that is accurately collected and processed. But no – my favorite is the one that depends on the amount of discussions between people. 🙂


    1. Hello Tom, thank you for commenting ! I doubt, that you are not qualified ! I do agree with your statements and plan to discuss this a bit more in the next post. Regarding your favorite metric, this is indeed a real thing, especially in manually operated FABs which have no or no reliable data due to missing equipment integration. I have seen manually build “heat maps” which were simply based on, was a tool group discussed as a problem in the morning meeting – YES or NO. I remember data like the top toolset was discussed on 24 days in the last month. Very likely worth to have a closer look, what is going on and how can it be improved.


  2. Pay attention to the bottleneck… unless it’s litho. Their tools are the most expensive so they must be a bottleneck by design.


  3. Yes indeed, in a lot of factories the Litho tools are the most expensive tool group and one would assume, that the Factory capacity is designed in a way, that the Litho tools are also the bottleneck. In daily FAB life I experienced often, that other tool groups became temporarily or permanently the true bottleneck for various reasons.


  4. True bottleneck is tool with the lowest Unit Start Capacity (USC), all other factors is also important but it is a matter of management – capacity variability management


    1. There is no option to edit my previous comment, I meant that bottleneck is toolset with lowest WSA- Wafer Start Achievable which is basically USC (of 1 unit) multiply by number of tools.


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