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In addition to offering the MTBF Reliability Prediction System, we also offer MTBF consulting services. We can do the MTBF reliability prediction calculations (ELK-MTBF_RPSW_MIL-HDBK-217, and/or ELK-MTBF-RPSW-Telcordia/Bellcore) for you, saving you the time and effort of doing the job yourself. If you need an MTBF calculation for your product ASAP, then our consulting solution may be perfect for you. Use our MTBF consulting services to take advantage of our 15+ years experience with MTBF predictions: please contact us for more information and a price quote.
FAQ(자주하는 질문 및 답변)
Q1: What Is MTBF?
Q2: What is MIL-HDBK-217?
Q3: What is Telcordia / Bellcore?
Q4: How do I choose: MIL-HDBK-217 or Telcordia / Bellcore?
A4: Your company's product and customer profile will quite often dictate which reliability prediction handbook to use. For example, you will probably use MIL-HDBK-217 if you have military or government customers, or commercial contracts or customers that specify 217 for reliability predictions. While MIL-HDBK-217 is widely used by both commercial and military companies, it is targeted for military applications, which might explain the somewhat pessimistic numbers it sometimes gives for commercial quality products. Thus, many of our commercial customers, making products such as computers, telecommunications systems, medical systems, and power supplies, choose to use the Telcordia / Bellcore handbook for their reliability predictions. Our informal tests comparing 217F-1 and Bellcore MTBF predictions indicate that Bellcore results are usually better (we saw 25%-270%). Also note that many of our commercial customers using Bellcore report that their predicted MTBF is consistent with their actual field experience.
When choosing between MIL-HDBK-217 and Bellcore, also keep these points in mind:
- Bellcore has 5 environment classifications (3 ground, 1 air, 1 space), while 217F-2 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 to get a more accurate prediction.
- While MIL-HDBK-217 is targeted for military applications, it does include commercial quality levels for all part models, and it is certainly appropriate to use 217 for commercial products. The Bellcore part models were originally developed and targeted for commercial applications.
- Bellcore simplifies the models by basing all part failure rates on ambient temperature only, while 217F-2 bases IC and semiconductor failure rates on part junction temperature. Thus, the Bellcore method is quicker and easier to use. For high power dissipation parts, note that our Bellcore version of RelCalc does allow you to bump up the operating temperature for any given part.
- The Bellcore 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.
- Bellcore 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 217F-2 approach requires more work, and our experience has shown that the 217F-2 SMT model contribution to the overall board failure rate is usually negligible.
- Both MIL-HDBK-217 and Bellcore are known and used worldwide.
If you have questions about choosing between MIL-HDBK-217 and Bellcore for your particular situation, please feel free to contact us at any time. Note that some 20% of our customers buy both versions giving them flexibility for different products, applications, customers, etc.
Q5: Do I need to buy the MIL-HDBK-217 or Telcordia / Bellcore handbooks?
A5: No. If you are using the RelCalc for Windows software, our documentation, help screens, and technical support should normally be sufficient to help you do your reliability prediction work. Note that we do not sell the actual handbooks; if you want to buy the handbooks, please contact us for details.
Q6: Why do I need to do reliability prediction?
A6: In today's very competitive electronic products market, a commitment to product quality and reliability is a necessity: customers have high expectations for the reliability of the products they buy, and the companies that don't meet those expectations lose. The American Electronics Association 1991 Productivity Survey rated product quality and reliability as the most important factor for success in high technology markets. The most successful companies meet these market demands for quality by using design for reliability principles: integrate reliability considerations into the entire product design process, right from the start. This way reliability is designed into the product, not patched on later, when problems arise. The companies that practice design for reliability find that it results in fewer design changes and iterations, lower manufacturing costs, lower warranty and service costs, more profit, and, most importantly, happy customers. An important element of the design for reliability process is reliability prediction, which allows you to predict product failure rates.
Q7: What are the uses of reliability prediction?
A7: Reliability predictions provide a quantitative basis for evaluating product reliability. The information a reliability prediction gives can be used to guide your design decisions throughout the development cycle.
- Feasibility Study: When an initial design concept is proposed, a reliability prediction can give you an idea of the feasibility of the design as far as reliability is concerned. Even though these early stage predictions are based on limited design information, and thus are approximate at best, they can give direction to your design decisions; many of these early design decisions may be critical to the success of the product. In addition, it can really pay to discover potential problems early, on paper, before time and money is spent on detailed design and development.
- Compare Design Alternatives: As your design moves through the early stages into more detailed design, you will make many decisions on design alternatives. Reliability predictions, along with other factors such as performance and cost, can be used as a basis for your decisions.
- Find Likely Problem Spots: At the detailed design level, reliability predictions can help you identify likely problem areas. The predicted failure rates will point you to parts, or part groups, which are high contributors to the product failure rate; these problem areas can then be addressed and improved.
- Trade-Off System Design Factors: There are many factors that determine the overall value of a product; functional performance, cost, size, weight, reliability, and other parameters must all be integrated for a successful design. The design process will thus involve many trade-offs among these factors; reliability predictions can offer a quantitative measure of reliability to guide your trade-off decisions.
- Track Reliability Improvement: As you progress through the design, reliability predictions can offer evidence of improving reliability, allowing designers, management, and customers to track progress toward reliability goals.
Q8: What are the ways to do reliability prediction?
A7: You can use various reliability prediction techniques, depending on your knowledge of the details of your design. An early estimate can be made by comparing your product with products of similar function or complexity, of known reliability; generally, this will be a crude estimate at best, as the many differences in design details between the products are not accounted for. As more details of your design are known, more accurate methods become available. These methods utilize part failure rate models, which predict the failure rates of parts based on various part parameters, such as technology, complexity, package type, quality level, and stress levels. Two of the better known failure rate prediction methods are MIL-HDBK-217 , and Telcordia / Bellcore . These handbooks offer documented procedures for predicting product reliability, providing a standard basis for comparing reliability numbers.
Q9: Why do I need RelCalc for Windows?
A9: You're finally convinced that you need to do a reliability prediction. You get one of the reliability prediction handbooks, grab your calculator and pencil, and start pounding away, and, pretty soon, "HEEEELP!!!". If you've ever done a prediction by hand you are already nodding your head in agreement; if you've never done one by hand, please talk to someone who has.
Reliability predictions include a large amount of tedious, time consuming, error prone computations; doing this by hand will quickly drive you crazy, while using the RelCalc for Windows software will almost make it fun. The time and money that the software saves will make it truly realistic for you to integrate reliability considerations into your design process. Doing a reliability prediction for a small 100 part circuit board could easily take 8 hours of hand computation; ELK-MTBF-RPSW allows you to crank it out in less than 2 hours. After your first computation at 35 degrees C, you might want to run a prediction at 45 degrees C: ELK-MTBF-RPSW will give you the new answer in a few seconds; manually, you'll have to recalculate the whole mess again, taking another 6-7 hours! Thus, the ELK-MTBF-RPSW for Windows reliability prediction software can turn the drudge into an organized and manageable tool usable throughout the design phase: it will allow you to quickly identify problem areas and parts; it will encourage you to experiment with design alternatives, such as part reduction, part selection, derating, burn-in, and others; it will allow you to keep up with reliability concerns as your deadlines get tighter.
The investment you make in the ELK-MTBF-RPSW for Windows reliability prediction software, a tool which can be used in your overall product reliability efforts, will be paid back many times over in the years to come: when you build reliable products, your reputation grows, your costs shrink, and your business prospers.