For electronic components, the two most popular and widely accepted models are MIL-HDBK-217 and Telcordia. Relex supports all of the reliability models listed below. Whether you are required to find a MIL-HDBK-217 or Bellcore MTBF or conduct an analysis using the RDF 2000 standard from France Telecom or the HRD5 standard from the UK, Reliability Prediction in Relex is the tool you need.

MIL-HDBK-217

MIL-HDBK-217 was the original standard for reliability. It was designed to provide reliability math models for nearly every conceivable type of electronic device. It is used by both commercial companies and the defense industry, and is accepted and known world-wide. It is sometimes referred to as MIL 217, MIL Handbook 217, MIL-217, MIL-217F, MIL-STD-217, or MIL-HDBK-217E, a previous revision. The most recent revision of MIL-HDBK-217 is Revision F Notice 2, which was released in February of 1995.

MIL-HDBK-217 includes the ability to perform a parts count analysis or a part stress analysis. A parts count analysis provides a simpler reliability math, and is normally used early in a design when detailed information is not available, or a rough estimate of reliability is all that is required. A part stress analysis takes into account more detailed information regarding the components, and therefore offers a more accurate estimate of failure rate.

Telcordia

The Telcordia reliability prediction model was originally developed by AT&T Bell Labs. Bell Labs modified the equations in MIL-HDBK-217 to better represent what their equipment was experiencing in the field. The main concepts in MIL-HDBK-217 and Telcordia (previously Bellcore reliability prediction) are very similar, but Telcordia added the ability to take into account burn-in, field, and laboratory testing. This added ability has made the Telcordia standard very popular with commercial organizations. Telcordia Issue 2 is the most recent version of this standard.

The Telcordia reliability prediction model also supports the ability to perform a parts count or part stress analysis, but in Telcordia, these different calculations are referred to as Calculation Methods. Telcordia offers ten different Calculation Methods. Each of these Methods is designed to take into account different information. This information can include stress data, burn-in data, field data, or laboratory test reliability data.

Although the use of Calculation Methods originated with the Telcordia Model, Relex has taken this concept one step further, and allows users to implement these Calculation Methods with all Relex-supported reliability models. This is just another example of the innovations that Relex offers.

Click here to read a comparison between the MIL-HDBK 217 and Telcordia standards.

Mechanical Model

In addition to the models used to predict the failure rate of electronic components, it was found that a model was required for mechanical components. The Handbook of Reliability Prediction Procedures for Mechanical Equipment (NSWC-98/LE1) fulfilled that requirement.

This Mechanical model, which was developed by the United States Navy, provides models for various types of mechanical devices including springs, bearings, seals, motors, brakes, and clutches. This is a relatively new standard, and currently the only one of its kind.

PRISM

PRISM is a standard for MTBF prediction and system reliability analysis, originally developed by the Reliability Analysis Center (RAC). Relex PRISM provides a number of specific analysis techniques. Applying process grades to a reliability analysis accounts for the process-related variability around the assembly or system failure rate. Incorporating predecessor data into an analysis factors in historical and predicted data when calculating the overall reliability. The Bayesian analysis technique facilitates the use of test and field data at the assembly level to enhance predicted component failure rates with real-life experiences.

217Plus

The 217Plus methodology is based on the RIAC-HDBK-217Plus, Handbook of 217Plus Reliability Prediction Models. This Handbook was published in May 2006 by the Reliability Information Analysis Center (RIAC), a Department of Defense Information Analysis Center sponsored by the Defense Technical Information Center. The Handbook of 217Plus Reliability Prediction Models contains the equations and model parameters that form the basis of the 217Plus methodology, which includes the ability to perform both Parts Count and Parts Stress analyses. The 217Plus methodology supports process grades, predecessor data, and Bayesian analysis.

CNET 93

CNET 93 (a.k.a. RDF 93) is a standard developed by France Telecom© that provides reliability models for a wide range of components. CNET 93 is a comprehensive model similar to MIL-HDBK-217, which provides a detailed stress analysis.

RDF 2000

RDF 2000 is a newer version of the CNET 93 standard, developed by UTE. It uses cycling profiles and their applicable phases to provide a completely different basis for failure rate calculations.

HRD5

HRD5 is a standard developed by British Telecommunications plc© that also provides models for a wide range of components. In general, HRD5 is similar to CNET 93 (a.k.a. RDF93), but provides simpler models and requires fewer data parameters for analysis.

299B

299B is based on the Chinese standard GJB/z 299B. It was translated into English by Beijing Yuntong Forever Sci.-Tech. Co. Ltd., and incorporated into Relex. 299B very similar to the MIL-HDBK-217 reliability standard, allowing you to take actual temperature and stress information into account.

Comparing Telcordia and MIL-HDBK-217

When selecting which model to use for the reliability prediction of electronic components, it is often helpful to be able to compare the two most common models to understand the differences. Based on the requirements of the reliability prediction analysis, it may be found that one model is more applicable under certain circumstances than the other. This comparison was designed to offer some understanding of the differences between Telcordia and MIL-HDBK-217.

There are numerous differences between the two models, and it would be very difficult to outline all of the intricate differences. However, when comparing the two models, it is often helpful to simply review the fundamental differences. These fundamental differences are outlined briefly below:

Recognition and Acceptance

Telcordia is primarily accepted in the United States. Although its popularity is growing internationally, it has not been completely embraced by the international community. Because MIL-HDBK-217 was the original standard for reliability prediction analyses, it is known and accepted world-wide. MIL-HDBK-217 is sometimes referred to as MIL 217, MIL Handbook 217, MIL-217, MIL-217F, MIL-STD-217, or MIL-HDBK-217E, a previous revision.

Concentration

When AT&T Bell Labs developed the Bellcore reliability model (now Telcordia), they concentrated primarily on commercial equipment. Understandably, the model was designed to focus specifically on telecommunications. MIL-HDBK-217, however, was much more broad in scope. MIL-HDBK-217 is geared towards both military and commercial equipment, and has no specific market focus.

Calculations and Equations

The basis of the Telcordia and MIL-HDBK-217 calculations are very similar. However, when comparing the calculations of the two models, it is often found that the Telcordia calculations are generally more optimistic than calculations in MIL-HDBK-217. In addition, the Telcordia calculations generally require fewer part parameters for components.

This comparison does not suggest, however, that Telcordia MTBFs and failure rates will simply always be better. It simply points out that, depending on the component types being analyzed, significant differences between MIL-HDBK-217 and Telcordia MTBFs and failure rates may be predicted.

Consideration of Test Data

As stated earlier, when the Telcordia model was established, it included the additional capability of considering burn-in data, laboratory test reliability data, and field data. This feature is extremely helpful in calculating failure rates that are based on historical data, rather than simply stress data. In addition, burn-in data is used to quantify the first year multiplier, which is an indication of infant mortality.

Although this concept originates from the Telcordia model, in Relex, users have the ability of using these additional calculation methods with any Relex-supported reliability model. Again, this is just another example of the flexibility of Relex.

Multiplier

The Telcordia model was designed to calculate failure rates in FITs (or failures in time). This value is expressed as failures per billion hours. This differs from MIL-HDBK-217, which was designed to calculate failure rates in failures per million hours.

Although this is a significant difference between the two models, it is a moot point in the Relex Software, because Relex gives its users the ability to specify what failure rate units they wish to use. Relex users can select to calculate failure rates in failures per million hours, failures per billion hours, or failures in any other unit that they require.

Parts

The part types that are supported between the two models do differ. Telcordia, for instance, supports additional miscellaneous part types in its model. Telcordia provides models for gyroscopes, batteries, heaters, coolers, and computer systems. These part types are not available in MIL-HDBK-217.

MIL-HDBK-217 also has special part types that it supports. MIL-HDBK-217 provides models for printed circuit boards, lasers, SAWS, magnetic bubble memories, and tubes. These part types are not supported by the Telcordia model.

An important point, however, is that Relex provides users with the ability to use either model for selected components. This means, for example, that the majority of the parts in an analysis may be evaluated using MIL-HDBK-217, but Telcordia could be used for those special part types that are not supported by MIL-HDBK-217 (or vice versa).

Environments

Because Telcordia was initially designed for use in the telecommunications industry, the operating environments that Telcordia supported were very limited. Initially, Telcordia only supported three different variations of Ground-based environments. However, Telcordia is rapidly evolving. In the most recent issue of Telcordia, additional operating environments of Airborne, Commercial and Space, and Commercial were made available. MIL-HDBK-217, on the other hand, has always offered a number of different operating environments. Currently, MIL-HDBK-217 supports a variety of ground, sea, air, and space environments.

Quality Levels

Telcordia makes the assignment of quality levels very simple. The current issue of Telcordia supports four standard quality levels. These quality levels are identical for all component types, and are simply based on some generalities regarding the origin and screening of components.

MIL-HDBK-217 offers a different approach to quality levels. In MIL-HDBK-217, the quality levels that are used differ from one part type to another. Rather than having a simple classification of general quality levels, the quality levels for components in MIL-HDBK-217 are derived from specific data that is component dependent. Therefore, the quality levels for resistors are different than the quality levels for semiconductors. The quality levels for semiconductors are different than the quality levels for integrated circuits. The quality levels for each part type were designed specifically for that classification of component.

Conclusion

Choosing one model or another is a decision which must be based on a wide array of factors specific to your application. Relex Software strives to empower you with a flexible system that allows you to create a package that best suits your needs. In fact, with Relex, you can combine both methods together, so you can utilize the best parts of both models to perform an analysis that most accurately reflects your design. Relex makes choosing reliability models easy!