Virtium Industrial SSD Temperature Screening Process
While there exists different classifications of NAND flash targeted for different applications, e.g. consumer/client, industrial/embedded, and enterprise/datacenter, this paper discusses the use of industrial/embedded in commercial (0°C to 70°C) and industrial (-40°C to 85°C) temperature ranges as part of solid-state storage devices.
This paper covers the standard temperature uprating process for the industry as well as the temperature uprating process for Virtium products and the benefits Virtium provides by screening commercial temperature rated components for use in industrial applications.
Solid State Storage Devices (SSD) play an increasingly essential role in both commercial and industrial applications, not only because of their size, weight, and power advantages but also because of their resilience to temperature.
Within the SSD, NAND is the primary flash-memory component and would be required to operate within specific temperature standards for the drive to be considered viable for industrial applications. Given the right temperature screening methodology, a process often referred to as “uprating”, commercial temperature NAND can be screened to verify their operability for use in high and low temperature industrial applications.
Leveraging a wealth of experience, Virtium has developed a comprehensive suite of screening and validation processes to produce SSDs that exceed industry standards for reliability and capability.
NAND Flash Fabrication and Screening Overview
NAND Flash Fabrication
A solid-state storage device, commonly referred to as a Solid-State Drive (SSD), consists of a controller, NAND flash, sometimes DRAM, and other electrical and timing components. Within these devices, NAND as the primary storage component of the drive.
During the fabrication process, individual NAND die are populated in quantity upon a single pure silicon wafer. Once fabrication is complete, each die on the wafer are probed-tested to assess its functional capability. During this classification, NAND die are sorted and binned based on their functional capability to ensure quality and reliability. NAND die deemed to be of the highest grade are typically reserved for use in data centers and other industrial applications.
Lower grade NAND die are often used for consumer-oriented applications where competitive pricing is of higher value than higher quality and reliability and where the usage characteristics are not as intense as would be with many data center and industrial applications.
Examples include retail USB and memory cards and lower end smart phones and tablets. Following probe-testing, the NAND wafer is cut into individual NAND die and then the die are packaged into either a ball grid array (BGA) or thin small-outline package (TSOP).
Additional burn-in processing may be performed once the NAND die are placed in the BGA or TSOP packages. From there, NAND may be re-rated to validate operating temperature ranges at the commercial grade range (0°C to 70°C) or industrial grade range (-40°C to 85°C). In general, a vast majority of NAND flash available in the market are only tested at the commercial temperature range while a smaller fraction may be screened at the higher industrial temperature required for industrial use.
Industrial and Commercial Temperature Screening
Commercial and industrial grade NAND are derived from the same fabrication process, and thus possess the same intrinsic device reliability; however, these components are screened under different ranges of operating temperature. NAND approved for commercial use are screened to function within a temperature range between 0°C to 70°C, while industrial NAND are screened to operate between -40°C and 85°C.
Within the industry, SSD manufacturers may opt to use NAND components that are pre-screened for industrial temperature range by the NAND manufacturer. However, this typically comes at a higher cost. Because commercial and industrial temperature components share the same wafer and die characteristics, SSD manufacturers may also choose to uprate commercial temperature components in-house by screening for the components’ functional capabilities over the industrial temperature range.
In some cases, SSD manufacturers with strategic relationships with NAND manufacturers can follow approved NAND screening processes approved by the NAND manufacturer, thus providing identical outcomes.
Industry Standard Temperature Screening
Temperature screening evaluates the capacity of the individual NAND or the complete drive to function beyond the temperature range screened by the manufacturer. It is also an accepted standard process across multiple industries. For instance, NASA and the US Department of Defense, which respectively holds the most stringent standards for components and utilizes its commercial off-the-shelf (COTS) program, are among the entities which accept temperature screening.
The temperature screening process is feasible because NAND die, regardless of rating, are fabricated together on the same wafer and designed to function within a significant temperature margin. While an individual NAND die may be approved by the manufacturer to operate within the commercial temperature range, with proper screening, inherently “stronger” die (fewer weak cells/bits) may also meet the specifications for industrial applications.
Temperature screening thereby validates that NAND currently approved for commercial applications are capable of meeting industrial applications as well. This process is critical to industry sustainability, as supply of commercial temperature NAND is generally greater and commands a lower cost when compared to the pre-screened industrial temperature rated NAND counterparts.
The Virtium Screening Process
Virtium Temperature Screening
Virtium screening involves an incorporated process that is executed at the module level to ensure the finished product performs reliably throughout its designated temperature range. By screening beyond individual component level, Virtium validates that each component of the drive works as stated and ensures