Burn-In Testing: How Much Reliability Is Worth the Extra Time?

Imagine an industrial electronic assembly that has passed its functional tests and is ready for delivery. Everything works as intended.

But the product is expected to operate reliably for years, perhaps inside a machine or system where an unexpected failure could mean downtime, a service visit, or an expensive replacement.

This is where an EMS provider may recommend an additional step: burn-in testing.

Instead of shipping the product immediately after the usual production tests, the electronics are operated for an extended period of time, often under elevated temperatures or electrical loads. The goal is to expose weaknesses that might not appear during a short functional test, but could lead to an early failure once the product is in the field.

That additional confidence, however, comes at a price.

Burn-in can add hours or even days to the testing process. It requires equipment, energy, monitoring and test capacity. For a highly critical aerospace application, that effort may be relatively easy to justify. For cost-sensitive high-volume electronics, the calculation can look very different.

And somewhere between those extremes sits a large part of industrial electronics.

So the real question is not whether manufacturers want reliable electronics. Of course they do.

The more useful question is:

How much additional testing is justified by the failure risk you are trying to eliminate?

To answer that, we first need to understand what burn-in testing is actually designed to find.

What Burn-In Testing Is Actually Trying to Prevent

A product passing its functional test tells us something important: it works at that moment and under the conditions in which it was tested.

What it does not necessarily tell us is how the product will behave after hundreds or thousands of hours in operation.

Electronic components and assemblies can contain latent weaknesses that do not cause an immediate failure. Manufacturing defects, weak components, soldering issues or material-related weaknesses may initially remain unnoticed and only become visible after the electronics have been operating for some time or have been exposed to thermal and electrical stress.

This is where the concept of infant mortality becomes important.

Reliability engineers often describe product failures using the so-called bathtub curve. At the beginning of a product's life, the probability of failure can be comparatively high because weaker units fail early. After this initial period, the failure rate typically decreases and remains relatively stable during the product's useful life, before increasing again as components eventually wear out.

Burn-in testing targets that first part of the curve.

By operating electronics for a defined period and under controlled stress conditions, manufacturers try to accelerate the appearance of early-life failures. The intention is not to simulate the entire lifetime of the product, but to identify units with weaknesses that could otherwise become failures shortly after delivery.

This distinction is important:

Functional testing asks whether the product works. Burn-in testing asks whether hidden weaknesses emerge when the product is operated under stress over time.

Burn-in therefore does not guarantee that a product will never fail. Nor does simply increasing the burn-in duration automatically make a product more reliable.

Its value lies in screening: identifying certain early weaknesses before the product reaches the field.

And that raises the next practical question: What actually happens to an electronic assembly during a burn-in test?

What Actually Happens During a Burn-In Test?

A burn-in test sounds simple in principle: operate the electronics for an extended period of time and see whether they fail.

In practice, the process is much more controlled.

Depending on the product and the test specification, an electronic assembly or complete system is powered and operated for a defined period while being exposed to elevated temperatures and electrical loads. Dedicated burn-in chambers or temperature-controlled environments allow manufacturers to maintain the required conditions while the devices continue to operate.

During this time, relevant parameters are monitored to detect failures or abnormal behavior. The idea is to create conditions that make certain latent weaknesses appear earlier than they would under normal operation.

But there is no universal burn-in recipe.

A test lasting eight hours at one temperature is fundamentally different from a test lasting several days under more demanding conditions. The appropriate temperature, duration, electrical load and monitoring requirements depend on the product, its components, the expected operating environment and, most importantly, the weaknesses the test is intended to reveal.

This is also why burn-in should not simply be understood as “putting electronics in a hot chamber for 24 hours.”

For some products, the electronics may operate continuously under relatively constant conditions. Other reliability screening approaches use changing temperatures, power cycling or additional environmental stresses. These methods are sometimes grouped together in everyday discussions, but burn-in and Environmental Stress Screening (ESS), for example, are not necessarily the same thing.

The important point for an OEM working with an EMS provider is that the test conditions should have a purpose.

The question is not how much stress can be applied, but which conditions are appropriate for exposing the failure mechanisms that matter for the product.

And once electronics have to remain in a controlled test environment for hours or even days, another factor quickly becomes important: production economics.

The Reliability–Time–Cost Trade-Off

If burn-in can expose early failures before a product reaches the customer, why not simply test every product for as long as possible?

Because reliability is not the only requirement in electronics manufacturing.

Every additional hour of burn-in requires test capacity. Products occupy equipment or chamber space, consume energy and need to be monitored and handled. Depending on the setup, a longer burn-in can also increase work in progress and extend the time before a finished product can be shipped.

At low volumes, this additional effort may be manageable. At higher production volumes, however, even a relatively small increase in test duration can have a significant impact on throughput and the amount of test capacity required.

This is where burn-in becomes more than a technical question. It becomes an economic one.

On one side of the equation are the costs of testing: additional production time, equipment, energy, capacity and ultimately higher manufacturing costs.

On the other side is the cost of not detecting an early failure.

For an industrial product, a field failure may involve much more than replacing a defective electronic assembly. A technician may have to travel to the customer, a machine may be unavailable while the problem is diagnosed, or a difficult-to-access system may need to be opened and repaired. In some applications, the cost of the electronic assembly itself can be small compared with the consequences of its failure.

This is why the same burn-in strategy does not make economic sense for every product.

An additional 24 or 48 hours of testing can look expensive for a high-volume, cost-sensitive product where a failed unit can be replaced relatively easily. The same testing time can look comparatively inexpensive when the electronics will operate inside an industrial system for years and an early field failure could result in substantial service effort or downtime.

The relevant comparison is therefore not simply the cost of burn-in versus no burn-in. It is the cost of additional screening versus the risk and consequences of an early field failure.

And those consequences vary enormously between applications.

That is why burn-in is particularly established in high-reliability environments, while in other applications the additional time and cost require much more careful justification.

To understand where that balance changes, it helps to look at how burn-in is used across different industries.

Where Burn-In Makes Sense and Where It Often Doesn't

There is no industry in which every electronic product automatically requires the same burn-in procedure. The decision depends on the product, its reliability requirements and, above all, the consequences of a failure.

Looking at different industries makes this easier to understand.

Aerospace and Defense: When Failure Is Extremely Difficult to Accept

Aerospace and defense represent one end of the spectrum.

Electronic components used in high-reliability space applications can be subject to extensive screening requirements. Depending on the applicable specification and reliability class, burn-in periods can extend far beyond what would be economically realistic for many commercial products.

For example, NASA/JPL documentation for high-reliability microelectronics describes burn-in periods of 160 hours for QML Class Q and 240 hours for higher-reliability Class V or Class S devices.

The economics are easy to understand: if electronics are installed in a system that is extremely difficult or impossible to repair after deployment, preventing an early failure can justify a substantial amount of additional testing. And in safety-critical applications, the consequences can go far beyond repair costs or downtime. An electronic failure may affect the safe operation of the entire system, making reliability not only an economic consideration, but a safety requirement.

In such environments, spending significantly more time on screening before deployment can therefore be entirely reasonable.

Medical Electronics: Reliability Depends on the Application

Medical electronics are another area where reliability can be particularly important. But it would be misleading to assume that every medical electronic device automatically requires burn-in.

The appropriate screening strategy depends on the device, its risk profile and the applicable product and quality requirements. In fact, FDA guidance on electronic-component screening does not establish burn-in as a universal requirement for medical-device manufacturers.

The important distinction is therefore not simply whether a product is "medical", but what the consequences of an electronic failure would be and which reliability measures are appropriate for that specific device.

Automotive: Reliability Meets Production Volume

Automotive electronics illustrate a different challenge.

Electronic systems may need to operate reliably for years while being exposed to temperature changes, vibration and demanding operating conditions. At the same time, automotive production can involve very high volumes, making every additional production step economically significant.

This creates exactly the trade-off at the heart of burn-in testing.

A documented example from automotive manufacturing used a temperature-cycled operational screen for electronic engine control units. The screening process helped identify intermittent component and workmanship defects and was integrated into the production sequence specifically because its duration was short enough to remain practical.

The lesson is important: an effective reliability screen must not only detect relevant weaknesses. It also has to fit the realities of production.

Industrial Electronics: Where the Decision Becomes Particularly Interesting

For many industrial electronics products, the answer is less obvious – and that makes the decision particularly interesting.

Consider a control unit installed inside a production machine.

The electronics may be expected to operate reliably for many years. If the assembly fails after a few weeks, replacing the PCB itself might not even be the largest cost. Troubleshooting, technician time, travel, machine downtime and disruption at the customer's site can quickly become much more significant.

In such a case, additional burn-in may be relatively easy to justify.

But change the scenario slightly. Imagine a less critical product that is easily accessible, inexpensive to replace and produced in much larger volumes. Suddenly, adding many hours of burn-in to every unit may be difficult to justify.

This is why industrial electronics are such a good example of the real burn-in decision.

There is often no simple rule saying that the product must or must not be burned in. Instead, the OEM and EMS provider need to understand the application, expected lifetime, operating environment, production volume and consequences of an early failure.

Consumer Electronics: When Cost and Throughput Dominate the Equation

At the other end of the spectrum are many cost-sensitive, high-volume consumer products.

This does not mean that burn-in is never used in consumer electronics. Components may already have undergone screening at semiconductor or component level, and individual products can have their own reliability requirements.

However, extensive system-level burn-in of every finished unit becomes harder to justify when production volumes are high, margins are tight and a failed product can be replaced relatively easily.

In these environments, manufacturers may rely on a combination of component qualification, process control, functional testing, sampling and other reliability methods rather than simply adding long burn-in periods to every finished product.

The comparison across industries reveals an important principle:

The more serious and expensive the consequences of an early field failure, the easier it becomes to justify additional screening.

But knowing that burn-in can make sense is still not enough. For an EMS provider, the practical question is when to recommend it to a customer in the first place.

When Should an EMS Recommend Burn-In?

For an EMS provider, burn-in should not simply be another test added to every production process. It should solve a specific reliability problem.

In some cases, the customer already defines burn-in requirements as part of the product specification or test plan. In others, the EMS may identify that additional screening is worth discussing based on the application, operating conditions or consequences of a potential field failure.

This is where the experience of the manufacturing partner becomes valuable.

An EMS that understands the product and its intended use can help the customer ask the right questions before deciding how much additional testing is appropriate.

What Happens If the Product Fails in the Field?

This is often the most important question.

If a failed assembly can be replaced quickly and at low cost, extensive burn-in may be difficult to justify. But if a failure causes machine downtime, requires a service technician, interrupts a production process or creates a safety risk, the economics change considerably.

The cost of failure should therefore be considered at system level – not only as the cost of replacing the PCB.

Where Will the Electronics Operate?

A control board operating in a climate-controlled office faces a very different environment from electronics installed in industrial machinery, outdoor equipment or systems exposed to elevated temperatures and demanding operating cycles.

Understanding the actual operating environment helps determine which stresses are relevant and whether burn-in is an appropriate way to address them.

How Long Is the Product Expected to Remain in Service?

Expected lifetime matters as well.

Industrial electronics are often expected to operate reliably for many years. In some applications, products may also become increasingly difficult or expensive to access, service or replace after installation.

That can make detecting weak units before delivery considerably more valuable.

What Are We Actually Trying to Detect?

This question is easy to overlook.

Burn-in should not be performed simply because "more testing is better." The test needs to target relevant early-life failure mechanisms.

If the expected weaknesses are unlikely to be revealed by the chosen temperature, electrical load or test duration, adding more burn-in time may provide little additional value.

The test strategy should therefore start with the failure mechanisms and reliability risks of the product – not with an arbitrary number of hours.

What Testing Is Already in Place?

Burn-in is only one part of a much broader quality and test strategy.

Depending on the product, manufacturing may already include inspection, electrical testing, functional testing and other environmental or reliability-related procedures. Components themselves may also have undergone qualification or screening before reaching the EMS.

The question is therefore not simply whether burn-in is beneficial in isolation, but what additional risk it addresses beyond the testing that is already being performed.

What Do the Specification and Customer Requirements Demand?

Finally, the decision is not always optional.

Specific customer requirements, product specifications or applicable qualification and screening standards may already define particular test conditions. In those cases, the role of the EMS is less about deciding whether burn-in should be performed and more about implementing the required process correctly and documenting the results.

In less prescriptive applications – including many industrial electronics projects – there may be considerably more room for discussion.

And this is where a good EMS can add value beyond manufacturing itself.

Rather than simply offering burn-in as another test service, the EMS can help the customer determine whether the additional screening addresses a meaningful product risk.

Once that decision has been made, however, another question remains: if burn-in is appropriate, how much burn-in is actually enough?

How Much Burn-In Is Enough?

Once burn-in has been identified as useful, the next question seems obvious: how long should it last?

Unfortunately, there is no universal answer.

Burn-in periods can range from hours to several days, depending on the product, components, applicable requirements and the purpose of the test. As we have seen in high-reliability aerospace applications, defined screening procedures can require well over 100 hours. That does not mean the same duration would make sense for an industrial control board.

More burn-in is not automatically better burn-in.

The purpose of the test is to expose relevant early-life weaknesses within a controlled period of time. If the chosen conditions do not effectively accelerate the failure mechanisms of interest, simply keeping the product in the test chamber for longer may add cost and production time without providing proportional additional value.

The opposite is equally important. A burn-in period chosen primarily because it fits conveniently into the production schedule may be too short or too mild to provide the intended screening effect.

This is why duration cannot be considered independently from the test conditions.

Temperature, electrical load, operating state, cycling and monitoring all influence what the test actually does. A meaningful burn-in specification therefore needs to define not only how long a product is tested, but also under which conditions and for what purpose.

For some products, these parameters are already defined by customer specifications, qualification requirements or established screening procedures. For others, particularly in industrial electronics, the appropriate approach may need to be determined based on the product's expected operating environment, known failure mechanisms, production volume and acceptable level of risk.

There is also an economic limit.

Beyond a certain point, extending the burn-in period may reveal fewer additional early-life failures, while the costs of equipment, energy and occupied test capacity continue to increase. Where that point lies depends on the product, the failure mechanisms being targeted and the test conditions.

Finding the right balance therefore means looking for sufficient screening to address the relevant early-life risk – not simply maximizing the number of hours.

The goal is not the longest possible burn-in. It is the shortest test that reliably achieves the required screening objective.

And that brings us back to the question we started with: how much reliability is actually worth the extra time?

Reliability Is a Risk Decision

So, how much reliability is worth the extra time?

There is no single number of burn-in hours that answers that question.

For a space application, spending days on additional screening can be entirely reasonable. For a high-volume, easily replaceable product, the same approach may make little economic sense. And for many industrial electronics applications, the right answer lies somewhere in between.

The deciding factor is not simply how reliable you want the product to be. Every manufacturer wants reliable products.

The more useful question is how much early-life failure risk the application can tolerate – and what the consequences are if a weak unit reaches the field.

If a failure means replacing an inexpensive and easily accessible device, extensive additional screening may be difficult to justify. If it means sending a technician to a remote site, stopping a production machine, accessing electronics installed deep inside a system or potentially creating a safety risk, additional testing can quickly become the less expensive option.

That is why burn-in should not be viewed as a standard step that is either "good" or "unnecessary."

It is one tool within a broader reliability and test strategy.

For OEMs and product teams, that means understanding the real consequences of failure before defining the level of screening they need. For EMS providers, it means going beyond simply offering burn-in as another item on a list of test capabilities. Their manufacturing and testing experience can help customers understand when additional screening addresses a meaningful risk – and when it may simply add time and cost.

The goal is not to test electronics for as long as possible. It is to test them as much as necessary for the product, the application and the risk you are trying to control.

And sometimes, the extra hours before shipment are a small price to pay for avoiding the wrong failure afterwards.