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Rework Under Control with MES

 · 5 min · Romeu Gonçalves

Keep rework under control with MES, boosting efficiency and product quality

Rework Limits Control V11.2
Rework is one of the hidden challenges in manufacturing, affecting costs, efficiency, and product quality. This blog covers how CM MES helps you to control rework, providing solutions to stop errors before they escalate. Beyond rework limits, the other powerful capabilities of our MES are also presented, from real-time visibility to quality enforcement.

Rework: A short introduction

Rework is the corrective process applied mainly to WIP that doesn't meet the specified quality standard during production. To ensure full traceability, it's usually performed in pre-defined and approved rework flows. For instance, in semiconductor industry, a wafer can be re-coated and re-exposed when photo-resist misalignment or contamination is detected during the inspection.

Besides ensuring traceability and recover value (instead of scrapping the WIP), it also helps to improve yield, customer deliveries and their quality requirements.



Can Rework be done indefinitely and without any control?

Theoretically, yes, if a robust control system is not in place on the shop floor. But we know that neither the customers nor the manufacturers want that. Unlimited rework increases costs and can sometime degrade the quality of the final product, among other issues.

It’s why it may be necessary to restrict the number of times a lot can be reworked due to quality concerns, or even forbidding rework at all. Lots can often only tolerate a limited number of reworks before they become unusable and, in some cases, rework may not be permitted at certain process steps or for specific reasons.

CM MES now provides a mechanism to restrict the number of reworks for materials:

  1. Global Limit by Product: Apply an overall rework limit for a specific product.
  2. Limit by Step: Define rework limits at specific process steps using a Smart Table
  3. Limit by Rework Reason: Restrict reworks based on the reason, using a Smart Table
  4. Combination of Limits: Apply these restrictions individually or in combination.

Taking the example above, the lithography process cannot be redone infinitely if misalignment continues to be found at the end of the process. Not to mention the cost of photoresist, labor, and the degradation of reticles, excessive rework can damage underlying layers, and it is better to reject a few misaligned or contaminated dies rather than scrap entire wafers.

Misalignment
Misalignment

Another good example happens in medical device manufacturing. In this industry, and especially for specific devices like catheters, rework is very limited or completely prohibited. Catheters come into direct contact with sensitive tissues like vein and urinary tract. Repeated rework can introduce contaminants, which might trigger infections or toxic reactions in the patient.

Catheter rework
Catheter rework

Rework Limits were introduced as an out-of-the-box feature in Version 11.2, but how was it managed in previous version when needed? Well, through extensibility, adding a few configuration tables some attributes and some business rules to implement the required rules. Now, although the situation could be overcome, having custom solutions is always less cost-effective than using out-of-the-box features.

How MES manages rework limits

In medical industry some products cannot perform rework at all, while others may be reworked but with limits.

For example, after an assembly process, if issues are detected in the component manually assembled, the lot can be sent to rework once to replace the affected components, however, if after the next inspection the same issues are detected again, the lot can no longer be sent to rework to replace the components, and in this case it must be placed on hold or a NCR must be opened.

Catheter assembly
Catheter assembly

In the following demonstration, both "Ester IV Catheter" and "Foley V Catheter" products share the same routing. Although rework flows are available, the lots from product "Foley V Catheter" cannot undergo to any rework while the other product may proceed with rework under defined limits.

The following configurations were defined for this demonstration:

Product properties:

Foley Catheter Rework Limits
Foley Catheter Rework Limits
Ester Catheter Rework Limits
Ester Catheter Rework Limits

Context resolution table configuration:

Step Rework Limits Context Smart Table
Step Rework Limits Context Smart Table
Reason Rework Limits Context Smart Table
Reason Rework Limits Context Smart Table

Here is a demo to show the configurations:

Rework features available in Critical Manufacturing MES

In addition to rework limits, these are the other available related features

  • Simple Design of Rework Flows
    Create and manage rework flows with an intuitive and streamlined approach.

  • Integration with Standard Process Steps
    Associate rework operations directly with standard manufacturing steps to ensure full process alignment.

  • Configurable Rework Reasons
    Define multiple rework reasons, with the ability to link different rework flows to specific process steps.

  • Flexible Return Points
    Configure rework flows to return materials to any designated step within the process flow.

  • State-Based Rework Application
    Control when rework can be applied by defining eligible states: Queued, In Process, or both.

  • Rule-Based Triggers
    Automatically execute predefined rules when a material is sent for rework — from simple notifications to advanced actions, such as initiating a warehouse transfer request to supply critical Moisture-Sensitive Level (MSL) components required for the rework operation.

  • Traceability and Data
    All operations are recorded, and data are available for reports and KPIs.

Final thoughts

Managing and Controlling rework is simple with Critical Manufacturing MES. It gives you the tools to prevent errors and improve results.

Author

Hi! My name is José Romeu Bogas Gonçalves. 😉

I’ve been with Critical Manufacturing since 2018, starting out as an MES Consultant. Earlier this year, I stepped into the recently created Advocate & Architecture team. My role sits at the intersection of technology, communication, and strategy. Making sure solutions are technically sound and that everyone understands how to use or build them.

You can check me on LinkedIn

Skills: MES Consultant | System Testing | System Modeling | User Training | Content Creating

Romeu Gonçalves
Architecture & Advocacy | MES