Working for manufacturer engineering couple years. Sharing the manufacturing experience, skill, DFx, design, and information. Be care of this blog is personal share and content may not be 100% correctly.
In the early days, when electronic component design and manufacturing were still in their infancy, burn-in (B/I) was widely used to screen out defective products. This process helped eliminate early failures before products reached customers, reducing the risk of complaints.
Statistical data shows that electronic products typically follow a bathtub curve in terms of lifespan. This means that failure rates are higher during the initial (infant mortality period or child mortality period) and end-of-life (wear-out period) phases, but once a product passes the early stage, its failure rate drops significantly and stabilizes close to zero (useful life period or normal period)—just like the shape of a bathtub.
Suggested Reading: What is Environmental Stress Screening (ESS)?
However, after decades of advancement, the electronics industry has matured. Today, most electronic components have high reliability and long lifespans, and early failures are rarely seen. This raises a critical question for the electronics assembly industry: Is burn-in still necessary? Many manufacturing companies have debated this topic, often without reaching a clear conclusion.
At Workingbear’s company, this discussion resurfaces every time a new manager takes over. Before deciding whether to continue or eliminate burn-in, it’s important to first understand what burn-in is, its pros and cons, and whether it is still necessary for your product.
What is Burn-In (B/I)?
Burn-in testing is typically conducted in a Burn-In Room under controlled temperature conditions. For example, the temperature may be set to 40°C ±5°C.
Why not raise the temperature even higher? A higher temperature would help detect more defective products.
Why not go beyond 60°C? Most engineering plastics may deform under continuous stress at temperatures above 60°C.
In addition, burn-in testing often includes power on/off cycling. This is crucial because electronic products experience a surge current when powered on—similar to the sudden force of a dam releasing water.
Why is this important? Surge currents can exceed the design limits of a product and push electronic components beyond their capabilities.
Why is this becoming less of an issue? Advancements in voltage regulation components and improved circuit designs have significantly reduced failures caused by power surges.
Burn-in is typically performed after product assembly. Once the burn-in process is complete, the product undergoes a final full test before shipping. The goal is to ensure that any defects triggered by burn-in are detected before reaching customers.
Since burn-in involves powering up the product, several key conditions must be controlled:
How often should the product be powered on?
How long should it remain on before shutting down?
How many on/off cycles should be performed?
What temperature should be maintained during the test?
Ideally, the burn-in process should allow the product to continuously run all its functions automatically, ensuring a thorough stress test.
Typical Production Flow with Burn-In Testing
Product Assembly + Initial Testing
Burn-In (B/I)
Final Full Testing + Packaging
Shipping
Advantages of Burn-In for Electronic Products
Burn-in helps screen out early-failure components and products. This was the original idea behind burn-in. As mentioned earlier, modern electronic components are generally highly reliable, and early failures are rare. However, burn-in can still help detect soldering issues such as cold joints, weak joints, or non-wetting in the manufacturing process. Additionally, burn-in can prevent companies from purchasing subpar components from suppliers with inconsistent quality. Price competition is relentless, and lower costs often come at the expense of quality.
Burn-in further ensures product quality before shipment. Some products may contain components from different batches or even different manufacturers. When combined, these components may cause unexpected issues, and burn-in can help identify such problems. For example, PCBs with BGA components are prone to HIP/HoP (Head-in-Pillow or Head-on-Pillow) defects. Performing functional tests during burn-in can significantly increase the chances of detecting these issues.
Burn-in gives production engineers more time to identify product instability. When a new product enters mass production, its quality is often less stable. Burn-in allows production engineers to fine-tune the process and stabilize the product before it reaches customers.
Disadvantages of Burn-In for Electronic Products
Burn-in requires additional space and power, increasing facility costs.
Burn-in extends production time, reducing shipping efficiency and inventory turnover.
Burn-in requires extra manpower, leading to higher labor costs.
Even with these pros and cons, the ultimate decision on whether to implement burn-in comes down to quality—and, more importantly, cost. There are both tangible and intangible costs to consider. Do you want to catch most product issues before shipment (tangible cost), or do you want to take the risk of dealing with customer complaints later (intangible cost)? Some managers choose to eliminate burn-in to cut visible costs, effectively turning the customer into their QA team. If product issues arise in the market, the decision-maker who removed burn-in may have already been promoted or moved on, leaving the remaining engineers to deal with the fallout.
To protect ourselves, we engineers still believe burn-in is necessary but have devised a gradual reduction strategy. When a product first enters mass production, we initially conduct 100% burn-in for 24 hours. Once yield rates reach a stable level, we reduce burn-in to 4 hours and remove some pre-burn-in test steps. When yield rates improve further, we switch to 4-hour burn-in on only 10% of units (sampling burn-in).
The reason we agreed to reduce burn-in time from 24 hours to 4 hours is based on statistical analysis. Our data showed that most failures occur within the first 4 hours of burn-in. However, different companies and products may exhibit different failure characteristics. Some products might reveal issues within 2 hours or even 1 hour, meaning they wouldn’t require a full 4-hour burn-in. Others may need even longer.
Challenges of Sampling Burn-In
Sampling burn-in has one major drawback: What happens if the failure rate exceeds the acceptable threshold?
Should the entire batch be scrapped or reworked?
How do you track and recall faulty products?
Should burn-in be reinstated to 100% until stability is restored?
Will the burn-in room have enough capacity to handle the increased workload?
To address these challenges, we try to make burn-in as automated as possible by allowing products to self-test all functions and record test data. This helps reduce unnecessary testing time after burn-in, maintaining product quality while optimizing efficiency.
What is “Run-In”? How is it Different from “Burn-In”?
Some factories use Run-In instead of Burn-In, but what exactly is Run-In? It’s somewhat similar to the concept of “warming up a car.” A common approach is to power on the product after assembly to ensure there are no immediate issues, then let the system run automatically for a short period—typically 30 to 120 minutes.
In some production lines, I’ve even seen assembled products powered on and sent into the air to “fly” around the factory, similar to how TSMC transports wafers overhead. This method prevents products from occupying valuable floor space. After completing a circuit around the factory, the product returns to the production line for final testing, inspection, and packaging before shipment.
Key Differences Between Run-In and Burn-In
One major difference is temperature control:
Burn-In requires a defined environmental temperature, often around 40°C ± 5°C, but never exceeding the material’s heat tolerance (e.g., plastic deformation temperature).
Run-In does not specify an environmental temperature—it simply runs the product at room temperature, which may vary based on location.
Strictly speaking, Burn-In is more rigorous than Run-In.
As for whether Run-In is effective, Workingbear suggests running a few test batches and analyzing the data before making a final decision. There’s really no definite answer—it depends on the product and manufacturing conditions.
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