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DfR Solution’s approach to thermal uprating is based upon a strong understanding of component functionality (the parametric behavior of crystals, NAND flash, IGBTs, etc.), expertise in the fundamental degradation behaviors that can be influenced by temperature (changes in RC behaviors, voltage sag, electromigration, etc.), and a thorough awareness of the two known industry standards that address this concern: EIA-4900 and IEC TR 62240.

As a first step in the process, DfR attempts to identify pertinent alternatives to uprating, such as:

• Use of a device from the same or a different manufacturer that meets the required temperature range
• Modifying or controlling the devices’ local operating environment so that the rated temperatures are not exceeded
• Negotiating with the device manufacturer to provide necessary assurance over the wider temperature range

Additional steps in the process include reviewing the part’s derating curves and understanding how drift in certain parametric outputs could influence the functionality of the circuit (this is often conducted using DfR’s expertise in circuit analysis) and requesting relevant temperature ranges from the part manufacturer in regard to junction temperature (not ambient or case temperature) and Absolute Maximum Rating (as opposed to Recommended Operating Conditions). An example of our philosophy toward uprating can be seen below in our response to a customer’s question regarding commercial vs. grade components. For more information on our uprating knowledge, please see our White Papers.

Question:

What is the root difference between commercial-grade and industrial-grade components? As to IC devices, there are two said about the screen. For one, the devices that can’t meet the industrial grade in the screen will be shipped as commercial grade. For another, these devices will be discarded. Which one is more rational?

Both are done, but the most common approach is after burn in (process applied to total lot/population), for the test criteria to be set for industrial temperature limits and some additional tests added when the line is producing industrial grade product. Most parts today have some performance margin due to more effective design rules and very good process controls. This explains why uprating may be possible.

Not all suppliers address multiple part grades the same way. Generally, screening or testing is typically performed at room ambient for key parameters as well as parameters with shifted limits defined by thermal correlations derived from device characterizations performed during device design qualification. This is the most common approach used to determine product grade. An understanding of the part manufacturer’s target customers should be developed. Since some part manufacturers target only commercial applications, their design rules and any subsequent part/parameter characterization may only be concerned with a limited temperature range and additional testing or characterization of wider temperature ranges is not performed, and device capability may indeed be unknown. However, many manufacturers provide both commercial and industrial grade devices, which can typically be assumed to follow similar design rules and are also often produced in the same foundries with the same processes. Some manufacturers may introduce parts initially in the commercial grade only until they have either sufficiently characterized he devices over a wider temperature range, or they have verified that fallout from any type of screen or binning tests are acceptable. Memory devices provided by Samsung and Micron appear to follow this scenario. From a rational standpoint, device manufactures will typically try to maximize profits from their target market.

NOTE: Due to shifting markets, and globalizing of processes, some manufacturers are changing their data sheets to reflect these goals and not the true capability of their parts. The caveat here is: “Know thy part supplier.”