Performing HALT in a nutshell (Highly Accelerated Life Test)

There are two primary opportunities for expensive defects to find their way into your products. The first is a design issue, typically a lack of margin in the design. When the product is first introduced in the field, these problems show up in a fraction of the products shipped and can become expensive warranty issues. Highly Accelerated Life Testing (HALT) is the tool to use to catch these design issues before the product is released to production. HALT helps you release a product that is mature and reliable, reducing warranty costs and increasing customer satisfaction.

The second opportunity for introducing reliability issues in your products is during manufacturing. A wide range of culprits can conspire to cause problems after the product design is ruggedized, including undetected shifts in supplied materials or components, production errors, process upsets, vendor changes or design changes with unexpected consequences and counterfeit components, just to name a few. Highly Accelerated Stress Screening (HASS) acts as a watchdog at the end of your production line, using a combination of extreme stresses to force defective products to fail before they get out the door.

Like HALT, HASS uses stresses beyond what the product will see in the field, and typically outside of the design spec for the product. These extreme stresses are what makes HASS so effective – and so fast! A typical HASS screen at the end of a production line will take just a few hours and will replace lengthy burn-in and other ESS tests, getting your products off the production floor and on the way to your customers more quickly, and with a higher level of reliability.

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HALT and HASS, Teamed Together to Improve Reliability

HALT and HASS are linked together. To implement HASS you must first do HALT, find and eliminate the weak links in your product’s design, then determine the actual operating and destruct limits of the final ruggedized design. These limits are guard-banded, then used as the basis for determining the level of stresses to use in HASS. Because the final limits found in HALT are typically significantly outside of the product specifications, the limits used in HASS are outside of spec as well. This lets HASS be an aggressive test, but still be safe (thanks to Proof of Screen – keep reading) for your product, because HALT has shown you the true limits of your design.

Proof of Screen – a Critical Step

Because HASS uses such extreme stresses, simply guard-banding the limits found in HALT is not sufficient to have confidence that the screen will not take excessive life out of the product and that it will, indeed, find the failure modes you expect it to catch. Proof of Screen is the empirical method used to demonstrate the safety and effectiveness of the screen. To demonstrate safety, known good products are run through the proposed screen 20 to 50 times, then tested to demonstrate that they were not adversely affected by these stresses. Because the design has been ruggedized using HALT it is typical for the products to function normally even after being exposed to such a high number of screening cycles. This portion of the Proof of Screen shows that one or two passes through the screen will not take an unacceptable amount of life out of the product.

To demonstrate the screen's effectiveness, it is necessary to run the screen on products that you expect to fail. These can be products with seeded defects, beta units that have come back from the field with No Defect Found types of failures, or down rev units with design issues that were identified and eliminated in HALT. By combining data about time to failure and stress levels used with the data from the safety portion of the Proof of Screen, a final screen that is safe and effective can be developed.

HASS Fixture Design

Designing a fixture to secure your products in the chamber during HASS requires a multifaceted approach, as there are several goals to be considered in the design. Of course throughput is a primary concern, so a HASS fixture is often designed to hold multiple products, with multiple fixtures in a chamber at once. It is important that these fixtures are designed so that all the products in all the fixtures are subjected to the same stresses, and that products are subjected to the same stresses from run to run. Ergonomic concerns become important, because manufacturing personnel must load and unload these fixtures multiple times a day. Also, the fixture must not introduce cosmetic damage to the product. A rigid fixture qualification process will show if these design goals have been adequately met.

How ESPEC’s Customer Solutions Group Can Help

If you are eager to get HASS implemented at your facility, the tasks of HASS screen development, Proof of Screen, fixture design and qualification may look daunting. Fortunately, ESPEC’s Customer Solutions Group can help with any or all of these challenges. Our engineers are experienced in all phases of HASS implementation, and we can offer whatever levels of assistance you may need. We can provide training and support while your engineers handle the actual implementation of the testing, or we can handle any portion of the implementation that you may not have the time or personnel to do on your own. Our goal is the same as yours – to make sure that you get a HASS procedure up and running in your facility as quickly and efficiently as possible. We want you to realize the reliability benefits of having the HASS watchdog on your production line, see your warranty costs drop and your customers’ satisfaction go up!

The Role of HASS in Quality Assurance

1. Detecting Defects Proactively

• HASS employs aggressive stress levels to subject products to accelerated aging conditions, simulating real-world operating environments.
• By applying these stress levels during the production phase, HASS can identify and mitigate manufacturing-induced defects before products are released to the market.
• This proactive approach helps manufacturers address potential issues early in the production process, minimizing the risk of field failures and warranty claims.

2. Enhancing Product Reliability

• By screening for defects that may have gone undetected during standard production tests, HASS contributes to enhancing product reliability.
• Identifying and addressing potential weaknesses early on ensures that products meet the highest standards of quality and reliability, reducing the likelihood of premature failures in the field.
• As a result, products subjected to HASS testing are more robust, resilient, and better equipped to withstand the rigors of real-world usage, thereby enhancing overall product reliability.

3. Improving Customer Satisfaction

• HASS testing plays a crucial role in ensuring customer satisfaction by delivering products that meet or exceed expectations.
• By minimizing the risk of product failures and defects, HASS helps manufacturers build trust and confidence among their customer base.
• Products that undergo HASS are more likely to perform reliably over their lifecycle, leading to greater customer satisfaction and loyalty.

4. Facilitating Cost Reduction

• Detecting and addressing defects early in the production process through HASS testing helps minimize warranty costs and avoid expensive product recalls.
• By proactively screening for potential issues, manufacturers can reduce the likelihood of costly field failures and associated warranty claims.
• Additionally, optimizing production processes based on HASS findings can lead to long-term cost savings by improving manufacturing efficiency and reducing scrap and rework.

Integrating HASS with Other Reliability Tests

HALT (Highly Accelerated Life Test)

While HALT focuses on identifying inherent design weaknesses and limitations, HASS complements this by screening for manufacturing-induced defects. By subjecting products to aggressive stress levels during the production phase, HASS can uncover new defects induced by supplier or manufacturing errors, providing a more comprehensive assessment of product reliability.

Environmental Stress Screening (ESS)

Environmental Stress Screening, such as burn-in, vibration and temperature cycling are often used to weed-out weak products prior to shipment. Burn-in testing involves subjecting products to prolonged operation under elevated stress conditions to identify and eliminate infant mortality failures. HASS can completely replace standard ESS, providing a more accelerated and efficient screening process for detecting potential defects, reducing the time and resources required for burn-in testing while still ensuring product reliability.

Overstressing Products

Challenge: There is a risk of overstressing products during HASS, which can lead to premature failures or damage to the units under test (UUTs).

Solution: Conducting a Proof of Screen (PoS) process before putting HASS on-line will conclusively demonstrate the safety and efficacy of the screen. PoS is a critical component of implementing HASS and is a professional service offered by the ESPEC Solutions Group.

Limitations Induced by Equipment with Limited Capabilities

Challenge: The effectiveness of HASS may be limited by the capabilities of the testing equipment, such as inadequate thermal ramp rates or thermal ranges, and/or vibration stresses.

Solution: Investing in state-of-the-art testing equipment with advanced stress application techniques can help overcome these limitations. By selecting the right equipment, manufacturers can ensure more accurate and reliable test results.

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Frequently Asked Questions

What is the difference between HALT and HASS?

HALT (Highly Accelerated Life Testing) focuses on identifying inherent design weaknesses and limitations, while HASS (Highly Accelerated Stress Screening) screens for manufacturing-induced defects during the production phase.

How does HASS testing improve product reliability?

HASS subjects products to aggressive thermal and vibration stresses, exposing potential infant mortality failures or other product defects rapidly and more effectively than classical ESS.

What types of products benefit most from HASS testing?

Electronics and electro-mechanical assemblies, particularly those with complex designs or critical reliability requirements, benefit most from HASS.

How long does a typical HASS test take?

The duration of a HASS test varies depending on factors such as product complexity and testing objectives, but it typically ranges from less than an hour to several hours.

Can HASS testing be applied to existing products, or is it only for new designs?

HASS testing can be applied to both new product designs and existing products to screen for manufacturing-induced defects and ensure ongoing reliability. If applied to an existing product for which HALT data does not exist, HALT will also need to be conducted on the product.