Just like the quotation in the movie “Apollo 132 ” and in real life, we design things not to fail. Your “friend” Murphy and Murphy Law ’s3 (see Figure 1 below) is out there waiting for you.
As a consultant, I get called on during various phases of a project to perform “failure analysis”.
Each phase of a project has unique failure signature patterns. Just like the bathtub curve in Figure 2, we see more “failures” in the initial design, development and early production “ramp up” phase.
As these failures are resolved, lower number of failures are exhibited throughout most of the product life cycle. Toward the “wear out” or legacy –“end of life” build there is an increase in failures until the end of the product life.
“Failure analysis is the process of collecting and analyzing data to determine the cause of a failure. It is an important discipline in many branches of manufacturing industry, such as the electronics industry, where it is a vital tool used in the development of new products and for the improvement of existing products. The failure analysis process relies on collecting failed components for subsequent examination of the cause or causes of failure using a wide array of methods, especially microscopy and spectroscopy5 .
What is Root Cause Analysis?
Root cause analysis (see Figure 3) can be summarized by a series of questions: What is the problem? Why did it happen? And what will be done to prevent it in the future?
Generally, the root cause failure analysis process can be divided into four parts or steps6
The first is defining the “problem”. For example, failure and type of failure (reliability, specification compliance, qualification, design to cost, delivery, functionality or catastrophic) would be typical failure mode signatures.
The second is performing the root cause analysis. Typical six sigma techniques like the 5 Why’s, brainstorming, scatter diagram, flow charts, run charts, histograms, control charts, tree charts, design of experiments, and the Ishikawa Fishbone Diagrams (see Figure 4), are used.
The third is root cause identification. This is the forensic portion where the underlying cause or causes are identified.
The fourth is recommendation, generation, and implementation of the solution.
From my experience here are some recommendations.
The first recommendation is to take good notes, document all experiments, guard and keep intact all failures as evidence as long as possible, assemble a team from the different disciplines, (engineering, quality, manufacturing, test, etc.) and summarize the failures and failure modes. The second is to understand the failure mode. Using a simple chart as shown in Figure 5 can help speed up and direct the failure analysis effort, which can be time consuming. Typically most companies are “under the gun” to resolve the problem quickly. It’s usually a financial burden or their customer needs product urgently.
The third is to keep an open mind of the root cause(s) and don’t jump to any conclusions. Always ask the question what changed?
As an example, I was called in where my client was having sporadic catastrophic MOSFET problems on a legacy product. After spinning our wheels for several days, we noticed that the MOSFET vendor was changed from the original supplier due to delivery problems. Both suppliers met the breakdown voltage but the original supplier was 20%-30% higher. Of course (Murphy’s Law) the voltage spike in the circuit was just higher than the new MOSFET breakdown voltage but lower than the original MOSFET breakdown.
Thus, the root cause was “not specifying the MOSFET breakdown correctly and with adequate margin” and not the fact that purchasing switched to a new vendor. A contributing root cause was not evaluating and qualifying a new supplier in the specific product. The corrective action was specifying a MOSFET with higher breakdown voltage and analyzing the voltage spike in the circuit to determine the adequate MOSFET breakdown voltage.
With increased integration of analog and digital functions and new microelectronic technologies our products are becoming very complex. This results in failure modes, which are very difficult to analyze and fix but by using six sigma tools and a team effort there is always a solution.
6 Root Cause Analysis For Beginners by James J. Rooney and Lee N. Vanden Heuvel
For Further Reading and Study:
Failure Analysis: A Practical Guide for Manufacturers of Electronic … By Marius Bazu, Titu Bajenescu
Microelectronics Failure Analysis: Desk Reference By EDFAS Desk Reference Committee
Root Cause Analysis: The Core of Problem Solving and Corrective Action By Duke Okes
RCA Root Cause Analysis Excellence in Problem Solving By Deepak Kumar Sahoo