7/30/2014 FAQ: How Do I Choose?

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How do I choose: Telcordia SR-332 or MIL-HDBK-217?Your company's product and customer profile will quiteoften dictate which reliability prediction handbook to use.For example, you will probably have to use MIL-HDBK-217if you have military contracts or customers, or commercialcontracts or customers that specify 217 for reliabilitypredictions.

While MIL-HDBK-217 is used by both military andcommercial companies, it is targeted for militaryapplications, which might explain the somewhatpessimistic numbers it sometimes gives for commercialquality products. Thus, most of our commercialcustomers, making products such as computers,telecommunications systems, medical systems, andpower supplies, choose to use the Telcordia SR-332handbook for their reliability predictions.

Our informal tests comparing 217 and Telcordia MTBFpredictions indicate that Telcordia results are usuallymuch better (we saw 25%-450%).

Based on reports from our customers, Telcordia seems togive much more realistic results than 217, and Telcordiapredicted MTBF results are likely to be more consistentwith actual field experience.

When choosing between MIL-HDBK-217 and Telcordia SR-332, also keep these points in mind:

- Telcordia has 6 environment classifications (4 ground, 1air, 1 space), while 217F2 has 14 environments (3ground, 8 air, 1 space, 2 sea). Thus, if your product isused in an air or sea environment, you might want to useMIL-HDBK-217.

- While MIL-HDBK-217 is targeted for militaryapplications, it does include commercial quality levels forall part models, and it is appropriate to use 217 forcommercial products. The Telcordia part models wereoriginally developed and targeted for commercialapplications.

- Telcordia simplifies the models by generally basing partfailure rates on ambient temperature, while 217F2 basesIC and semiconductor failure rates on part junctiontemperature. Thus, the Telcordia method is much quicker

7/30/2014 FAQ: How Do I Choose?

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and easier to use. For high power dissipation parts, notethat our Telcordia version of RelCalc does allow you tobump up the operating temperature for any given part.

- Telcordia SR-332 Issue 3 allows you to specify an UpperConfidence Level (UCL) for the calculations. MIL-HDBK-217 does not specify UCL for its calculations.

- The Telcordia model provides a measure of infantmortality failure rate in addition to the steady stateuseful operating life failure rate, and allows you tospecify system, board, and device level burn-in toimprove the infant mortality failure rate. MIL-HDBK-217only calculates the steady state failure rate.

- Telcordia does not have a specific SMT device model,saying that its data shows no significant differencebetween conventional and SMT device failure rates. MIL-HDBK-217F-2 does include a specific SMT model, whichwas developed to assess the life integrity of leadless andleaded SMT devices. The 217F2 approach requires morework, and our experience has shown that the 217F2 SMTmodel contribution to the overall board failure rate isusually negligible.

- The Telcordia failure rate models are more up to datethan the 217 models.

- Telcordia handles larger gate count ICs much betterthan 217.

- Both MIL-HDBK-217 and Telcordia are known and usedworldwide.

If you have questions about choosing between MIL-HDBK-217 and Telcordia SR-332 for your particularsituation, please feel free to contact us at any time. Notethat some 20% of our customers buy both versions (wegive a substantial price discount for the second version),giving them flexibility for different products, applications,customers, etc.

Copyright (c) 2014 T-Cubed Systems, Inc. All rights reserved.RelCalc (R) is a registered trademark of T-Cubed Systems, Inc.Phone: 818-991-0057 Fax: 818-991-1281E-mail: info@t-cubed.com Web: www.t-cubed.com