Reliability Validation Testing vs. End-Of-Line Quality Control

In this article, I will explain the difference between reliability validation testing and end-of-line quality control, because they are often mixed up when people talk about reliability testing vs quality control, yet they address very different risks.

What is reliability validation testing?

When we talk about reliability validation testing, I am talking about validating the product design, including the choice of components; in other words, product design validation from a reliability standpoint.

The idea is to expose the product to conditions that are close to, or beyond, its normal operating conditions and then observe whether it is likely to fail once it is in use. I am really asking:

“Given how this product will be used and given what environmental conditions it will have to endure, is the design likely to fail too early?”

To simplify, this is not about checking whether a batch was manufactured correctly. It is about confirming whether the reliability is adequate, or whether some aspects of the design or components make failures likely in the field (e.g. in customers’ hands, after installation, etc.).

What is end-of-line quality control?

On the other hand, end-of-line quality control (EOL QC) is about checking and confirming that the product has been manufactured properly.

Here, the question is as follows:

“Does this batch of products, which is coming out of the factory, comply with specifications?”

End-of-line quality control is a form of manufacturing quality control. It is a verification against specifications: appearance, dimensions, basic functions, and other points that have been agreed upon. It is usually not destructive, and it is not done beyond the normal operating conditions of the product.

So, when we discuss reliability testing vs quality control, End Of Line QC clearly sits on the “quality control” side. It takes a snapshot of what the products are now; it does not focus on whether the design itself will hold up over time in terms of being reliable.

Different risks: Design reliability vs manufacturing quality

These two activities target different types of risks:

1. Reliability validation testing tackles the risk that the design itself, including the components, is likely to fail after some time once the product is in use.
2. End-of-line quality control tackles the risk that a batch of products has been manufactured in the wrong way (for example, due to process issues, mistakes, or other production problems).

That’s really the core of design reliability vs manufacturing quality. There is a bit of overlap, but the root causes and corrective actions are quite different depending on whether the problem arises from design or manufacturing.

Ongoing reliability testing from production batches

One point that sometimes confuses people is ongoing reliability testing.

If needed, it is possible to pull some samples from production for ongoing reliability testing at the same time as the regular end-of-line quality control inspections. Just to be clear, those samples are tested with a different objective in mind: checking whether reliability performance has changed, not checking day-to-day manufacturing quality.

Why do experienced companies keep them separate?

Because the objectives and the risks are so different, every experienced company keeps reliability validation testing and end-of-line quality control separate.

They are done at different times, as the design needs to be validated before production starts. They typically involve different people, as product designers usually don’t work closely with the operations of purchasing & manufacturing.

FAQs

• Q: Is reliability validation testing the same as normal production testing?
  No. Reliability validation testing is about challenging the design, often close to or beyond normal operating conditions. Normal production testing (end-of-line QC) is about checking that each batch is manufactured according to the specifications.
• Q: Can strict end-of-line quality control replace reliability validation testing?
  No. Even very strict EOL quality control, including a bit of abuse and endurance testing, is not likely to tell you whether the design is likely to fail after some time in the field. It is good at confirming whether the products comply with the specifications and pass function tests.
• Q: Why pull extra samples for ongoing reliability testing if I already do EOL QC?
  Because EOL QC confirms manufacturing quality on that batch, while ongoing reliability testing aims at noticing differences in component manufacturing and in assembly methods that are likely to impact product reliability (and often also safety).