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How
do I choose: Telcordia SR-332 or MIL-HDBK-217? Your company's product and customer profile will quite often dictate which reliability prediction handbook to use. For example, you will probably have to use MIL-HDBK-217 if you have military contracts or customers, or commercial contracts or customers that specify 217 for reliability predictions. While MIL-HDBK-217 is used by both military and commercial companies, it is targeted for military applications, which might explain the somewhat pessimistic numbers it sometimes gives for commercial quality products. Thus, most of our commercial customers, making products such as computers, telecommunications systems, medical systems, and power supplies, choose to use the Telcordia SR-332 handbook for their reliability predictions. Our informal tests comparing 217 and Telcordia MTBF predictions indicate that Telcordia results are usually much better (we saw 25%-450%). Based on reports from our customers, Telcordia seems to give much more realistic results than 217, and Telcordia predicted MTBF results are likely to be more consistent with 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, 1 air, 1 space), while 217F2 has 14 environments (3 ground, 8 air, 1 space, 2 sea). Thus, if your product is used in an air or sea environment, you might want to use MIL-HDBK-217. - While MIL-HDBK-217 is targeted for military applications, it does include commercial quality levels for all part models, and it is appropriate to use 217 for commercial products. The Telcordia part models were originally developed and targeted for commercial applications. - Telcordia simplifies the models by generally basing part failure rates on ambient temperature, while 217F2 bases IC and semiconductor failure rates on part junction temperature. Thus, the Telcordia method is much quicker and easier to use. For high power dissipation parts, note that our Telcordia version of RelCalc does allow you to bump up the operating temperature for any given part. - Telcordia SR-332 Issue 4 allows you to specify an Upper Confidence Level (UCL) for the calculations. MIL-HDBK-217 does not specify UCL for its calculations. - The Telcordia model provides a measure of infant mortality failure rate in addition to the steady state useful operating life failure rate, and allows you to specify system, board, and device level burn-in to improve the infant mortality failure rate. MIL-HDBK-217 only calculates the steady state failure rate. - Telcordia does not have a specific SMT device model, saying that its data shows no significant difference between conventional and SMT device failure rates. MIL-HDBK-217F-2 does include a specific SMT model, which was developed to assess the life integrity of leadless and leaded SMT devices. The 217F2 approach requires more work, and our experience has shown that the 217F2 SMT model contribution to the overall board failure rate is usually negligible. - The Telcordia failure rate models are more up to date than the 217 models. - Telcordia handles larger gate count ICs much better than 217. - Both MIL-HDBK-217 and Telcordia are known and used worldwide. If you have questions about choosing between MIL-HDBK-217 and Telcordia SR-332 for your particular situation, please feel free to contact us at any time. Note that some 20% of our customers buy both versions (we give a substantial price discount for the second version), giving them flexibility for different products, applications, customers, etc. |
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