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All articles listed in reverse chronological order.

by Kirk Gray Leave a Comment

Why Parametric Variation Can Lead to Failures and HALT Can Help

Why Parametric Variation Can Lead to Failures and HALT Can Help

Kirk Gray, Accelerated Reliability Solutions, L.L.C.

Many reliability engineers have discovered HALT will quickly find the weaknesses and reliability risks in electronic and electromechanical systems from the capability of thermal cycling and vibration to create rapid mechanical fatigue in electronic assemblies. Assemblies that have latent defects such as cold solder or cracked solder joints, loose connectors or mechanical fasteners, or component package defects can be brought to a detectable, or patent, condition by which we can observe and potentially improve the robustness of an electronics system. [Read more…]

Filed Under: Articles, NoMTBF

by Fred Schenkelberg 1 Comment

Root Cause Knowledge and Models

Root Cause Knowledge and Models

Two short questions to evaluate your knowledge of failure mechanisms (root causes) and common reliability models. The answers will be posted in a comment, later.

Which of the following failure root causes is most likely NOT due to power line variation (electronic-based product)?

A. Circuit design margin exceeded
B. Power dissipation
C. In-rush current response
D. Mechanical fatigue [Read more…]

Filed Under: Articles, CRE Preparation Notes, Reliability Testing Tagged With: failure mechanisms, reliability models, root cause

by Fred Schenkelberg 3 Comments

Two Pumps Problem

Two Pumps Problem

Let’s say we have two identical pumps share a load in parallel. The failure rate for a pump in this mode of operation is 0.0002 failures per hour. If one pump has to carry the full load alone, that pumps failure rate increases to 0.0009 failures per hour.

What is the reliability of the two pump system over a 168 hour week of operation? [Read more…]

Filed Under: Articles, CRE Preparation Notes, Reliability Modeling and Predictions Tagged With: Failure Rate, Reliability block diagrams and models

by Kirk Gray Leave a Comment

Reliability Paradigm Shift From Time to Stress Metrics

Kirk Gray, Accelerated Reliability Solutions L.L.C.

Traditional electronics reliability engineering began during the period of infancy in solid state electronic hardware. The first comprehensive guide to Failure Prediction Methodology (FPM) premiered in 1956 with the publication of the RCA release TR-1100:  “Reliability Stress Analysis for Electronic Equipment” presented models for computing rates of component failures.  “RADC Reliability Notebook” emerged later in 1959, followed by the publication of a military handbook know as  that addressed reliability prediction known as Military Handbook  for [Read more…]

Filed Under: Articles, NoMTBF

by Fred Schenkelberg Leave a Comment

Permutations and Combinations

Permutations and Combinations

A foundational element of probability and statistics is counting. How many ways could something occur? A simple example is a pass or fail criteria, thus when evaluating a product there are two possible outcomes. [Read more…]

Filed Under: Articles, CRE Preparation Notes, Probability and Statistics for Reliability Tagged With: Basic Probability Concepts

by Fred Schenkelberg 7 Comments

Hypergeometric Distribution

Hypergeometric Distribution

In those situations where we sample without replacement, meaning the odds change after each sample is drawn, we can use the hypergeometric distribution for modeling. Great, sounds like statistician talk. So, let’s consider a real situation. [Read more…]

Filed Under: Articles, CRE Preparation Notes, Probability and Statistics for Reliability Tagged With: Discrete and continuous probability distributions, Hypergeometric Distribution

by Kirk Gray Leave a Comment

What will Advance Reliability Engineering?

What will Advance Reliability Engineering?

Kirk Gray, Accelerated Reliability Solutions, L.L.C.

In all aspects of engineering we only make improvements and innovation in technology by building on previous knowledge. Yet in the field of reliability engineering (and in particular electronics assemblies and systems), sharing the knowledge about field failures of electronics hardware and the true root causes is extremely limited. Without the ability to share data and teach what we know about the real causes of “un-reliability” in the field, it is more easily understood why the belief in the ability able to model and predict the future of electronics life and MTBF continue to dominate the field of electronics reliability [Read more…]

Filed Under: Articles, NoMTBF

by Fred Schenkelberg 2 Comments

Poisson Distribution Calculation

Poisson Distribution Calculation

Let’s say the results of software testing averaged three defects per 10,000 lines of code. The criteria for release is 90% probability of 5 or fewer defects per 10k lines.

If this product ready for release?

The Poisson distribution is appropriate here as it is useful for modeling defects per unit, count per area, or arrivals per hour. If the data, in this case, the defect count per lines of code to be modeled by the Poisson distribution, the probability of an occurrence (defect in this case) has to be proportional to the interval (lines of code in this case). Also, the number of occurrences (defects) per interval must be independent (more on statistical independence in another post). [Read more…]

Filed Under: Articles, CRE Preparation Notes, Probability and Statistics for Reliability Tagged With: CDF, cumulative distribution function, Discrete and continuous probability distributions, Exponential Distribution, PDF, Poisson Distribution, probability density function

by Kirk Gray Leave a Comment

For Maximum Test Value, Take it to the Limit!

For Maximum Test Value, Take it to the Limit!

When we go to an automobile race such as the Indianapolis 500, watching those cars circle the track can get fairly boring. What is secretly unspoken is that everyone observing the race is watching for a race car to find and sometimes exceed a limit, finding a discontinuity. The limit could be how fast he enters a curve before the acceleration forces exceed the tires coefficient of friction, or how close to the racetrack wall, he can be before he contacts it and spins out of control. Using the race analogy, [Read more…]

Filed Under: Articles, NoMTBF

by Fred Schenkelberg 17 Comments

Calculating Lognormal Distribution Parameters

Calculating Lognormal Distribution Parameters

The lognormal distribution has two parameters, μ, and σ. These are not the same as mean and standard deviation, which is the subject of another post, yet they do describe the distribution, including the reliability function. [Read more…]

Filed Under: Articles, CRE Preparation Notes, Probability and Statistics for Reliability Tagged With: Discrete and continuous probability distributions, function, Lognormal Distribution, reliability, Standard Deviation

by Richard Coronado 1 Comment

Hypothesis Testing

Hypothesis Testing

This week in our CRE Test Prep class/webinar we covered the Advance Statistics section of the CRE Primer, and I felt great that we stayed an hour more going over these though topics.

One of the topics was Hypothesis Testing.

Let me share some of the questions that arose during that section. [Read more…]

Filed Under: Articles, CRE Prep, CRE Preparation Notes, Probability and Statistics for Reliability Tagged With: Hypothesis Testing (parametric and non-parametric), statistics

by Richard Coronado 1 Comment

Confidence Limits

Confidence Limits

Last week during our CRE Test Prep class, we were covering the Basic Statistics section in the CRE Primer and had several questions regarding Confidence Limits for Reliability.

All of them were fair questions, and when students are asking these types of questions, the class gets better… [Read more…]

Filed Under: Articles, CRE Preparation Notes, Probability and Statistics for Reliability Tagged With: Statistical Interval Estimates, statistics

by Fred Schenkelberg 9 Comments

ALT and HALT

ALT and HALT

The other day I got a question about the difference between ALT and HALT. There was some confusion probably because of the similar words in the acronym. ALT is Accelerated Life Test, and HALT is Highly Accelerated Life Test. [Read more…]

Filed Under: Articles, CRE Preparation Notes, Reliability Testing Tagged With: Accelerated life tests, Discovery Testing

by nomtbf Leave a Comment

MTBF Eradication

After a discussion with a client this morning, and their motor vendor’s reliability engineer asked for a reference for a sample size calculation formula I recommended, I had a short email exchange with said reliability engineer. In my note with the references, I included an aside with a link to this site. He liked the site and agreed that MTBF was often [Read more…]

Filed Under: Articles, NoMTBF

by Fred Schenkelberg 7 Comments

Effective FMEA Principles

Effective FMEA Principles

Failure mode and effects analysis, or FMEA, is a tool for the identification and prioritization of possible ways a product or process can fail. The intent is to use that information to make improvements to the product or process.

I think of FMEA (and related processes like FMECA, dFMEA, etc.) as structured brainstorms that provide a means to focus on what’s important. [Read more…]

Filed Under: Articles, CRE Preparation Notes, Reliability in Design and Development Tagged With: FMEA and FMECA

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