Failure rate for given semiconductor device is simply determined by reading value of normalized junction temperature from printout for any given combination of ambient temperature, stress ratio, and maximum rated junction temperature, and obtaining corresponding failure rate from graph

Trivedi, S. N.

English

NASA Technical Reports Server

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NormalizedJunctiort Temperature
June 1973	 B73-10196 
NASA TECH BRIEF 
•	 Lyndon B. Johnson Space Center 	 A 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
An Improved Method for Obtaining a Normalized 
Junction Temperature for Semiconductors: A Concept 
The problem: 
To date, reliability of semiconductors has been deter-
mined through laborious, expensive, and time consuming 
computations. Typically a knowledge of thermal resist-
ance and of actual junction temperature are required to 
compute the basic reliability indicator, the normalized 
junction temperature. For a trade-off study of various 
stress loads and temperatures to which the device will 
be subjected, it is also necessary to calculate the actual 
power dissipation of the device. 
Failure Rate For Different Semiconductor Devices 
As A Function Of Normalized Junction Temperature
The solution: 
Most of these calculations have become unnecessary 
as a result of a recently developed method. No longer 
is there a need to know the thermal resistance and 
actual power dissipation of the device to determine the 
normalized junction temperature. 
How it's done: 
Failure rates for different semiconductor devices 
have already been established (see figure) as a function 
of normalized junction temperature. Hence, the only 
question remaining is to determine the value of normal-
ized junction temperature for any given device. The 
equation for normalized junction temperature T is 
given by
(TA - TS) + S(Tj(max) - TA)
Tj(max) - TS 
where TA 1S the ambient temperature; Ts is the temper-
ature at which the power derating begins, usually at 
25° C; S is the stress ratio; and Tj(max) is the maximum 
rated junction temperature. With T5 = 25° C, this 
equation has been processed by computer for all practical 
combinations of TA, S, and Tj(max). As a result, about 
1600 values of Tn have been printed out. Now failure 
rate for a given semiconductor device is simply deter-
mined by reading the value of Tn from the printout for 
any given combination of TA, S, and Tj(max) and 
obtaining the corresponding failure rate from the graph 
(see figure). 
T = 
• (continued overleaf) 
This document was prepared under the sponsorship of the National	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19730000196 2020-03-17T07:09:10+00:00Z
Note: 
Requests for further information may be directed to 
Technology Utilization Officer 
Lyndon B. Johnson Space Center 
Code JM7 
Houston, Texas 77058 
Reference: TSP73-10196
Patent status: 
NASA has decided not to apply for a patent. 
Source: S. N. Trivedi of

Martin Marietta Corp.

under contract to

Johnson Space Center 
(MSC-14136)
. 
B73-10196	 Category 01


An improved method for obtaining a normalized junction temperature for semiconductors: A concept

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