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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum ( )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Posted by: Al Johnson ( )
Organization:Analogic Corporation
Date posted: Tue Nov 17 17:17:25 US/Eastern 1998
Subject: Theta (jc) by Package Type
I am a Reliability Engineer performing stress analyses on medical and computer equipment. Stress analysis requires Theta (jc) as a data entry field. Many specification sheets do not have Theta (jc), C/W. Also, 217F Theta (jc) by package type is very inadequate. Is there a current Theta (jc) by package type available?


Subject: Thermal Resistance, junction to case
Reply Posted by: Bruce Dudley ( )
Organization: Reliability Analysis Center
Date Posted: Thu Nov 19 9:46:59 US/Eastern 1998
The Thermal Resistance values presented in MIL HDBK 217 are default values to be used as a last resort in estimating the thermal load on the device. Therefore, are very conservative. Part vendors have the best information on resistance factors based on their experience with the technology. If no information is available from one vendor, try another vendor with similar technology to see if they have a thermal resistance value. If they do, use it as substitute. The last published source of Thermal Resistances per package type was: RADC TR-86-97 Thermal Resistances of Joint Army Navy (JAN)Certified Microciruit Packages by Douglas Holzhauer. This document was produced in 1986, as result, it is probably useless for the new package and devices.

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