The Unexpected Impact Of Lots On Hold

Unusual ways manufacturing schedules can be derailed.


One of the biggest bottlenecks in any Subcon is Lots on Hold. The problem occurs many times a week on most factory floors. It’s something you’ve grown to loathe or endure. But, is there something you can do to reduce the amount of time lots spend on hold? In this article, we will explain what Lots on Hold are and how you can make the process less painful for your team and help improve on-time delivery to your customers.

Lots on Hold are lots that are temporarily suspended during testing due to a concern about yield, the failure rates of certain bins or the quality of testing. Parameters are set and when a lot exceeds the limits the lot is put on hold and investigated.

When something is askew, the lot is put on hold. The technician on the floor investigates. Typically the technician is not the product expert. In some companies (for example IDMs), the product engineer may be nearby and can come and investigate it. For the majority of Subcons and IDMs, it’s a more onerous, manual task that takes time and could lead to human error.

The technician has a template where they describe the problem. They send it to the person or team familiar with the product. The person could be in a different timezone, country and speak a different language. They must wait until the person gets the message, deciphers the error message, figures out what happened, and decides the next steps, then relays the message back to them. Sometimes, they may as well send a message in a bottle.

In many Subcons, lots can remain on hold for several days or more. We’ve seen lots remain on hold for over a week.


  • Time: With so much back and forth, a good lot could be held for a few days.
  • Production: With the lot on hold, unexpected retesting can affect capacity, which even if slight can affect delivery of other product.
  • Delivery schedule:The delivery schedule could easily be affected especially for the product in question but also, as just noted, other product using the same equipment.
  • Analysis: Generally, the technician uses different analysis tools to the product experts. Different tools have different algorithms, user interfaces and graphical representations. So they may not look at the same thing. If the technician sends their data in one format and the recipient uses different software to open it, it could corrupt the analysis.

I used to work in a translation agency where we could charge by word count. Invariably, the word count according to Excel was different from the word count determined by CAT tools and different from manual counting. The difference may be minuscule, but it slows things down. In the semiconductor industry, accuracy is essential, so using the same analysis tools is invaluable. For that reason, many of our customers share the analysis on-line with customers. It makes their lives easier and gives their customers peace of mind.

This can happen during wafer sort and final test. The factor delaying everything often isn’t with the behavior of the lot itself, it’s with communication. Until the issue is resolved the lot is on hold and cannot leave the factory floor.

yieldHUB helps automate the communication of Lots on Hold to save time, enhance collaboration, and reduce human error. It allows your team to spend less time filling out forms and waiting for answers. They will spend more time doing value-added activities.

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