JEDEC
STANDARD
Application Thermal Derating
Methodologies
JEP149.01
(Editorial Revision of JEP149, November 2004, Reaffirmed September 2019)
JANUARY 2021
JEDEC SOLID STATE TECHNOLOGY ASSOCIATION
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JEDEC Publication No. 149.01
-i-
APPLICATION THERMAL DERATING METHODOLOGIES
Introduction
Derating refers to the method of setting a value within the manufacturer's specifications for
environmental or operational maximum use conditions. This practice has been used to provide
greater functionality margin within the manufacturer's specifications, and, with the assistance of
the manufacturer, potentially extend useful life or increase reliability. The process presented here
is not a casual analysis, but is intended to be a part of a more sophisticated application analysis
process performed by highly informed engineering staff working closely with the respective
experts from the component manufacturer(s).
Derating can be used as a mitigation response to various uncertainties surrounding:
the specification limit given by the component manufacturer,
the actual use environmental conditions,
the approximate nature of mathematical models normally employed.
Traditionally, users of electronic components have employed various methods for derating.
They include assigning a maximum percentage of the manufacturer specification limit, setting
absolute limits, or absolute margin value from the manufacturer specification limit.
While design margin is desirable, stacking of multiple sources of margin can result in high costs,
lost opportunities and, potentially, increased failures (i.e. some failure mechanisms are inversely
dependent on temperature). Sources of margin include:
conservative estimates of the operational characteristics of the application,
component manufacturer specification limit margin,
application derating methods.
The practice of derating requires a good understanding of the manufacturer’s absolute
maximum ratings, specification limits, and the consequences of approaching them. These
ratings should have their foundation in the physical failure mechanisms and performance
limitations associated with the component or technology in question. Also needed is a good
understanding of the application use conditions and how the appropriate stress conditions can
be derived from them for comparison to the manufacturers specification limits. This illustrates
the need for close communication with the component manufacturer. Manufacturer’s
specification limits are typically derived from a combination of technology capability, design,
margin and marketing objectives. It should be noted that many of these limits are interrelated
with other specifications, such as the junction temperature relationship with ambient air or case
temperature through the thermal resistance of the various mechanical interfaces between
them. Where such interrelationships exist, prudent derating of selected operational,
performance or environmental conditions may make it possible to extend other specification
limits such that the application required performance and reliability meet requirements. In these
cases, the parameter or physical element most closely connected with the associated failure
mechanism or required functional performance takes precedence. For example, if
electromigration is a concern and it is affected by junction temperature, then junction
temperature should be managed. Adjustments can occur with other related elements so long
as the junction temperature is within the desired limits. These elements may include ambient
air temperature or thermal resistance through thermal planes or heat sinks, power dissipation
through clock speed, operational voltage, output drive (fan-out) or others.
