Cheryl Tulkoff - Design for Excellence in Electronics Manufacturing

Obsolescence management

Long‐term storage issues

Counterfeit prevention and detection strategies

Baseline life‐cycle cost (estimated total ownership cost)

Use environment verification

Corrosion protection and mitigation

Supplier auditing and vendor maturity and stability

Root cause analysis (RCA) is a generic term for diligent structured problem‐solving. Over the years, various RCA techniques and management methods have been developed. All RCA activities are problem‐solving methods that focus on identifying the ultimate underlying reason a failure or problem event occurred. RCA is based on the belief that problems are more effectively solved by correcting or eliminating the root causes, rather than merely addressing the obvious symptoms. The root cause is the trigger point in a causal chain of events, which may be natural or man‐made, active or passive, initiating or permitting, obvious or hidden. Efforts to prevent or mitigate the trigger event are expected to prevent the outcome or at least reduce the potential for problem recurrence.

Effective failure analysis is critical to product reliability. Without identifying the root causes of failure, true corrective action cannot be implemented, and the risk of repeat occurrence increases.

This chapter outlines a systematic approach to failure analysis proceeding from non‐destructive to destructive methods until all root causes are conclusively identified. The appropriate techniques are discussed and recommended based on the failure information (failure history, failure mode, failure site, and failure mechanism) specific to the problem. The information‐gathering process is the crucial first step in any failure analysis effort. Information can be gained through interviews with all the members of the production team, from suppliers, manufacturers, designers, reliability teams, and managers to end‐users.

Topics to be covered include:

Root cause problem‐solving methodology

Root cause failure analysis methodology and approach

Failure reporting, analysis, and corrective action system (FRACAS)

Failure mechanisms

Continuing education and improvement activities

The authors hope this book helps you to manufacture your products with better reliability and greater customer satisfaction.

A comprehensive, well‐thought‐out reliability program ensures that companies can achieve their quality, reliability, and customer satisfaction targets on time, on schedule, and within budget. Reliability is the measure of a product's ability to perform a required function under stated conditions for an expected duration. By definition, reliability is specific to each application – there is no one‐size‐fits‐all definition. So, it can be useful to start with what reliability is not along with some common myths about reliability.

Myths of Reliability

Myth 1: Don't worry about design, because most problems are caused by defects from suppliers. While many product failures can be traced back to supplier or manufacturing issues, the most severe warranty issues tend to be design related. Design flaws can affect every product at every customer. As a result, design issues are more likely to result in a recall and have a much more significant impact on a company's bottom line.

Myth 2: The design is intended for more rugged environments; therefore, nothing can be learned from consumer electronics. The stresses experienced during the operation of a computer or mobile phone can far exceed any loads applied to military, avionics, and industrial designs. For example, laptop computers left in the back of a car can experience temperatures as high as 80 C on a hot summer day. Combine that with component temperatures that can exceed 100 C during operation and products can be exposed to thermal cycles in number and severity that exceed those experienced in commercial and military applications.

Myth 3: Design verification is the same as product qualification. The purpose of design verification is to understand the margins of a design. This is typically performed on prototype units using small sample sizes (one to three units is common). Tests performed during design verification include highly accelerated life testing (HALT), corner‐case testing, UL testing, ship‐shock, etc. Once the design is proven to be robust, product qualification can then be performed. The purpose of product qualification is to demonstrate that design and manufacturing processes are sufficiently robust to ensure the desired quality and lifetime. Product qualification should be performed on a pilot production, not prototypes, and should have a sufficiently large sample size (5 to 20 units) to have some confidence in capturing gross manufacturing issues. There are substantial risks in performing product qualification tests on prototypes. Prototypes that pass qualification may not be representative of production units. This increases the risk of qualification testing failing to capture potential field issues. If prototypes fail qualification testing, these failures may be irrelevant, and attempts at root‐cause identification may be a misuse of time and resources.

Myth 4: Highly accelerated life testing (HALT) can be used to demonstrate product reliability. HALT demonstrates product robustness. Only accelerated life testing can demonstrate reliability. What's the difference? Robustness is the measure of a product's ability to withstand stress. For example, one inch of steel is more robust than one mil of paper. This measurement is often defaulted to time zero, which can be either immediately after manufacturing or when the product first arrives at the customer. Reliability is the measure of a product's ability to perform a required function under stated conditions for an expected duration.

Myth 5: Reliability is all predictive statistics. Companies that produce some of the most reliable products in the world spend a relatively insignificant percentage of their product development performing predictive statistical assessments. For example, many original equipment manufacturers (OEMs) in telecommunications, military, avionics, and industrial controls require a mean time between failures (MTBF) number from their suppliers. MTBF, sometimes referred to as average lifetime, defines the time over which the probability of failure is 63%. The base process of calculating MTBF involves applying a constant failure rate to each part and summing the parts in the design. While there have been numerous claims over the years of improvement on this number by applying additional failure rates or modifying factors to consider temperature, humidity, printed circuit boards, solder joints, etc., there are several flaws to this approach. The first is misunderstanding what it means. The average engineer often expects a product with an MTBF of 10 years to operate reliably for a minimum of 10 years. In practice, this product will likely fail far before 10 years. Second, the primary approach for increasing MTBF is to reduce parts count. This can be detrimental if the parts removed are critical for certain functions, such as filtering, timing, etc., that won't affect product performance under test, but will influence product reliability in the field.Unlike many other elements of the design and development process, reliability requires thinking about failure. For example, successful reliability testing requires failure, unlike most other forms of testing, where the goal is to pass.

Best Practices