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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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Original Message:

Posted by: S.Arun Kumar ( )
Date posted: Wed Feb 9 8:02:39 US/Eastern 2005
Subject: PRISM Model for PCBs
We are in the process of predicting the FR for an Electronic Assembly consisting of Through Hole Components and SMT Components. We are using a technique of Mixed model Prediction, in the sense that we use PRISM Models for the Passives and some standard ICs. For Connectors, Crystals & Coils we are using MIL 217FN2. When we want to compute the FR for PCB, we were not able to find a model for it in PRISM. We are Currently using MIL 217FN2 for PCBs. Now the Questions we have are Q1. How do I compute the Failure Rate for the PCBs using PRISM. Q2. In MIL 217FN2 we have Model for PTH and SMT Version of the PCB. My Query is that since we take the solder joint factor, Cycling Rate Factor for most of the components we are using in PRISM, do we need to separately calculate the FR of the PCB (SMT Technology).


Subject: PRISM Models for PCBs
Reply Posted by: ddd ( )
Organization: RAC
Date Posted: Thu Feb 17 15:03:05 US/Eastern 2005
The PRISM tool incorporates extensive field reliability databases that can be used to assess the failure rates of components where PRISM predictive models do not exist. PRISM also allows user input of data. If a user has field experience or test data, this data can be factored into an analysis. The name for a PCB in PRISM is “Circuit Card Assembly, Unpopulated”. Solder joint contributions will be included for any components where a PRISM RACRates model was used. Solder joint failure rates will need to be calculated for any components predicted by MIL-HDBK-217 or other sources. Cycling power is included in all the PRISM reliability models. Other models may or may not have cycling conditions.

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