CRE Preparation Notes

Prep notes for ASQ Certified Reliability Engineer exam ISSN 2165-8633

The CRE Preparation Notes series provides you with short practical tutorials on all the elements that make up the ASQ CRE body of knowledge. The articles provide introductory material, basics, how-tos, examples, and practical use guidance for the full range of reliability engineering concepts, terms, tools, and practices.

Keep your knowledge fresh by regularly reviewing topics and tools that make up reliability engineering.

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You will find the most recent tutorials in reverse chronological order below.

by Fred Schenkelberg 2 Comments

8 New Topics in the ASQ CRE Body of Knowledge

Last week we reviewed the 10+ topics removed from the CRE body of knowledge (BoK). This week, let’s look at the additions.

Three of the additions are new categories or groups of topics that in part contain new topics. There are five new topics, that in most cases included bits and pieces of concepts buried in the previous BoK.

Let’s take a look at each additions in a bit more detail. Some I agree with, some I wonder what the motivation is behind the addition, and some I question why it is included. [Read more…]

by Fred Schenkelberg 3 Comments

10+ Dropped Items from the ASQ CRE Body of Knowledge

A Review of the 2018 ASQ CRE Body of Knowledge

I just noticed the new 2018 ASQ CRE Body of Knowledge had been posted on the ASQ site. The new BoK will be in effect for CRE exams as of January 2018. Thus, we have six months to adjust to the new body of knowledge.

This is part 1 of a multipart review of the new BoK. Here we’ll look at the parts that those preparing for the exam will not have to master or review. There are 10+ topics dropped completely or in part from the BoK.

In future articles, we’ll review what has been added, what has been changed (a review), and how to best prepare for exams based on the new BoK. Plus, we can look over past BoK’s to understand where reliability engineering practice is today.

In part, the logic is these sets of tools (topics) that are not widely used by working reliability engineers. In some cases, I agree, and in others, I don’t. Let’s look at the eight topics not found in the upcoming CRE BoK. [Read more…]

by Fred Schenkelberg 4 Comments

The Eyring Model

The Eyring Model for Accelerated Testing

Sometimes the reaction rate of a process relies on two stresses. For chemical reactions, temperature seems to influence the rate of the reaction. Yet, other stresses such as humidity or voltage may also play a significant role.

H. Eyring suggested a model that assumes the contribution of each stress on the reaction rate is independent; thus one could multiply the respective stress contributions to the rate of reaction.

The Eying model provides a means to account for the contributions of temperature and another stress when modeling the time to failure of select failure mechanisms. [Read more…]

by Fred Schenkelberg 1 Comment

Waterfall Test Planning

A Waterfall Test Planning Approach to Product Reliability Environmental Testing

I may have the name, waterfall, used incorrectly here.

Years ago I learned from a former Apple reliability group manager how to organize reliability and environmental related testing where samples cascade through a sequence of stress conditions and evaluations. He called it waterfall testing. [Read more…]

by Fred Schenkelberg 1 Comment

ALT Allocation of Test Units

One question that you should consider when planning multiple stress accelerated life test (ALT) is the allocation of test units to the various stresses.

We want to create a model detailing the relationship between stress and time to failure. We also want to project the time to failure estimates to use conditions. Ideally, we test at nominal conditions only and gather time to failure information. We do not have the luxury of time thus explore using ALT.

One method of allocation is to place an equal number of samples with each stress level. Is that the best approach? [Read more…]

by Fred Schenkelberg 2 Comments

Electromigration Accelerated Life Testing

Black’s Equation

Black’s equation for estimating the time to failure due to electromigration is a classic. James Black explored and wrote about electromigration in aluminum metallization within semiconductors since 1969.

He and others have explored other materials used as conductors prone to electromigration. Thus, there are a number of models and constants available to match your particular system.

Let’s take a look at the general equation for a microcircuit conductor after a brief description of the failure mechanisms called electromigration. [Read more…]

by Fred Schenkelberg 3 Comments

Metal Fatigue Failure Mechanism Accelerated Life Testing

Metal is a wonderful, strong, material. Yet under certain types of stresses metal can fail One in particular is fatigue due to cyclic motion.

Metals in a solid state have an atomic level lattice structure. This provides the strength and flexibility. It is the flexibility part that causes trouble. We don’t get the benefit of flexibility for free. As the metal bends it ‘adjusts’ the lattice to accommodate the motion. In doing so, it changes the metal properties becoming a bit more brittle, for example.

In most cases a very small motion causes imperceptible changes and loss of functionality. In some cases, like bending a wire coat hanger with the intent to break it, just a few cycles of dramatic bending is enough to break the wire.

In metal applications that experience cyclic motion and the risk of metal fatigue failure may occur during the expected duration of product use, we may need to characterize the time to failure behavior. An accelerated life test for a metal fatigue failure mechanism is not difficult, yet does take some planning to get meaningful results. [Read more…]

by Fred Schenkelberg 22 Comments

Temperature & Humidity Accelerated Life Testing

Peck’s Relationship

High temperature & humidity is a common test condition. For specific failure mechanisms, there are models available (or you can create a model) to determine the translation from test to use conditions.

These acceleration models generally only apply to one specific failure mechanisms and do not apply to a system level estimate of life. If the failure mechanism is the dominant failure mechanism for the product, then an ALT exploring just that mechanisms would provide a life estimate.

Peck’s relationship is an acceleration model for the effect of humidity on the metallization elements of integrated circuits within plastic enclosures (typically an epoxy over molding). [Read more…]

by Fred Schenkelberg Leave a Comment

Time Compression Accelerated Life Testing

The Easy One

The easiest ALT is one that you operate an item more often then operated by the customer. Removing spans of time the item is not being bent, moved, heated, etc allows you to use time compression.

For example, a home kitchen toaster may be used for a few cycles during breakfast time in your home. In the lab, we can avoid having to wait the day of idle time and just make toast more often than just at breakfast to accelerate the operation of a toaster.

Time compression ALT is also easy to understand and describe the acceleration factor to cover the ALT results to field use conditions. Let’s explore a simple example, work out the acceleration factor and how to interpret a set of ALT results. [Read more…]

by Fred Schenkelberg 7 Comments

4 Different Types of Reliability Testing

Getting the Right Information from Your Reliability Testing

You cannot test in reliability any more than you can test in quality. Often reliability testing is done though, and knowing the range of testing approaches and their associated results will help you get the most information from each test conducted.

Let’s explore the types of testing that generate information useful as you develop a reliable product. There are 4 different types of reliability testing:

Discovery
Life
Environmental
Regulatory

Within each type there are many variations to the testing details and the specific results generated. Understanding the questions each type of testing has the capability to resolve is a good first step to implementing the right set of tests for your project. [Read more…]

by Fred Schenkelberg 3 Comments

4 Steps to Accomplish HALT

4 Not Always Easy Steps

Highly Accelerated Life Testing, HALT, is a method to discover the weaknesses in a design. Using a step stress approach of single and combined stresses, you can quickly expose the salient weaknesses in your design and/or assembly process.

The value of HALT is it’s quick and often finds problems not previously known. You will destroy one or more prototypes, yet the value of knowing specifically what needs improvement more than justifies the sacrifice of a few photos.

Conducting HALT may be part of your reliability plan. Keeping a few steps in mind will help make sure your HALT does provide value back to your development efforts. [Read more…]

by Fred Schenkelberg Leave a Comment

Taguchi Design of Experiments Approach

Dr. Taguchi was an engineer, not a statistician. He considered the ability of design of experiments (DOE) to identify and reduce sources of variability, yet needed a system that did not require a statistician to implement.

Dr. Taguchi proposed a few considerations for those applying the Taguchi design of experiments approach. [Read more…]

by Fred Schenkelberg 2 Comments

Taguchi’s 3 Fundamental Concepts

Taguchi may be best known for the variation of design of experiments that bear his name. Yet the impact of his work is felt across the product life cycle and all of the quality field.

Building on Deming’s observations that 85% of poor quality is due to faulty processes and only 15% due to the worker, Taguchi focused on creating robust processes.

A robust system is one that tolerates the daily and seasonal variations of the environment, machine wear, and equipment part-to-part variation, etc. A robust system operating in the range of real world conditions. [Read more…]

by Fred Schenkelberg Leave a Comment

You Are a Reliability Leader, Now Make a Difference

Your Reliability Engineering Leadership Role

Leadership is not a position or title within an organization. It is an attitude.

You’ve seen the internet meme’s about the difference between leadership and management. There is a difference and while not everyone is going to be in top management, everyone can (and should) be a leader.

As a reliability professional, you are conveniently looked to for leadership. You are expected to use your knowledge and skill to solve problems. To help teams solve problems. To improve the reliability performance of your system and across your industry. [Read more…]

by Fred Schenkelberg 3 Comments

Introduction to the Quality Triangle

Priorities and Balance

Have you ever worked on a project with no deadlines, unlimited resources, and boundless scope? Probably not.

Quality Triangle-1 — The Quality Triangle

You may have worked under the guidelines of a quality triangle, also known as a project management triangle, iron triangle, or project triangle.

Why is that? Why the limits to our ability to create a product or improve a system?

First, the world we work and live within has limits. We have only so much time for work, only the available resources, and limited knowledge. We do our best with what we have to work with at the time.

Second, as I once was told while working on an accelerated test design, ‘if there isn’t a deadline, you’ll happily tinker with the plan and get the testing done.’ My boss was right of course.

The set of constraints shape our projects and products. By understanding the set of constraints, specifically how they frame decisions, then we can complete complex projects. [Read more…]