Memory

Testing to ensure flash storage in rugged environments

20th April 2020
Alex Lynn
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When industrial product OEMs such as those in automotive, aerospace, and transportation need flash storage, it must be designed and tested to provide mission critical reliability despite regular subjection to vibration or temperature extremes in harsh environments. 

Failing to do so risks costly failure in the field that can potentially involve liability if safety is jeopardized, along with serious field service and warranty costs.  In the transportation industry, for instance, the unexpected loss of vital data could compromise safety features that drivers rely upon to prevent accidents.  In manufacturing automation, data device failures can cause machinery to malfunction, potentially causing safety issues along with production slows or stoppage.

Although industrial flash storage is designed to be rugged, different applications have different operating requirements.  So, customizing the flash storage device to ensure mechanical ruggedness is necessary to ensure reliability while providing applicable memory capacity and form factors.

While most of the flash storage industry promotes testing to ensure product performance within specified temperature ranges, industrial flash storage manufacturers that are committed to high reliability will exceed minimum standards.  When industrial product

OEMs experience flash storage card failures, one of the most common issues is that previous testing did not appropriately replicate real-world conditions for qualification testing.

“The only way that industrial OEMs can be assured that their products will withstand real-world vibration and temperature abuse is to put the flash storage components through the paces with accelerated tests like HALT (Highly Accelerated Life Test) and HASS (Highly Accelerated Stress Screen),” said Tony Diaz, Product Manager for Delkin Devices, a value-added supplier of non-volatile flash storage solutions in a variety of SSD, card and module solutions.

HALT and HASS techniques shortcut and avoid the problems of slower traditional methods that only test to minimum specifications and nothing more.  The accelerated techniques quickly expose any weak links in a product by testing well beyond minimum specs so that any reliability problems can be fixed before they become expensive field service, warranty, or liability issues. 

Accelerated qualification testing

During HALT testing, according to Diaz, products are exposed to the kinds of extreme environmental conditions that they might be subjected to after they are installed. The temperature is raised and lowered repeatedly and the memory device is exposed to high levels of vibration. The exact conditions used during HALT can be adjusted to meet specific OEM needs.

“There are four steps to HALT: thermal step testing, rapid thermal cycling, vibration step testing, and combined environment testing,” added Diaz.  “One computer manages the testing conditions while another runs the host application in which the memory will be used to emulate real operating conditions as closely as possible.”

Diaz, whose company performs HALT and HASS accelerated testing as well as Design Verification Testing (DVT) and Ongoing Reliability Testing (ORT), says that these results are analyzed in-house so that any necessary design changes can be made efficiently and effectively before the flash storage is used in any industrial OEM devices. 

HASS testing, which is a screening method used to monitor the quality and uniformity of manufacturing by finding production flaws and defects in products, is often used after HALT testing, as the two are complementary.

HASS is performed on a component based on the results of the preceding HALT. The HASS screening stresses are based on the limits identified through HALT, and combinations of stresses are applied simultaneously. The screening pushes the product beyond its operating limits until product failures are caused and any inherent defects are revealed.

Because the stresses in HASS are more rigorous than those rendered by conventional approaches, the testing accelerates the detection of design issues, so the problem can be corrected and the flash storage device ruggedized to prevent failure in the field.

“Product can often be improved before design release by testing to failure utilizing HALT and HASS,” said Diaz. “Typically, these tests are used to insure when a design goes to production that it exceeds its promised specifications whether in temperature, vibration, or other areas.” 

According to Diaz, often with such testing improvements can be discovered that allow a product’s design to exceed the specifications listed.  For example, traces can be modified or pad sizes reduced or increased to improve soldering when breaks or bad electrical connections are found.  Alternatively, connectors can be changed or repositioned to improve overall part performance or longevity.

One of the best ways for industrial OEMs to ensure that a storage device will work as expected in operating conditions is to partner with a manufacturer who offers accelerated testing reliability services.  Such testing helps to determine not only failure modes and root causes but also the functional operating limits and destruct limits of flash storage cards.  This information can be used to make necessary corrective improvements to significantly improve product reliability.

“The test process up to the release of a new design for production is often like a test of all the parts in the chain,” concluded Diaz. “The most likely weakest link is improved or replaced, then testing is resumed.  Then the second weakest link is determined and improved.  This process continues until a part well exceeds it specifications, so we can be sure the design and material are solid, and assurances can be taken this part in mass production is going to exceed the promised specifications in all areas.”

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