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5 Methodology steps to 6 sigma in electronics printed circuit board assemblies

By Lee Whiteman

An electronics manufacturer building one million circuit boards at 3 sigma levels would build 66,807 defective circuit boards. Assuming each defective board required $100 worth of parts and labor to repair, it would cost $6,680,700 to complete the repairs.

SOMEONE ONCE ASKED ME why 6 sigma is important in electronics. Why is there such a push for continuous process improvement at the design and manufacturing levels? From a practical sense, the real question should be: Can a company afford not to implement processes that will ensure 6 sigma quality?

Dense ball grid array (BGA) packages in electronics packaging routinely contain over 1,000 solder bumps. At minimum, there will be over 2,000 interconnections within the package that contain solder bumps and wire bonds between the package and die.

It is not beyond imagination that a printed circuit board could have over 100,000 interconnections – solder bumps and wire bonds – within the completed printed circuit board assembly.

For argument’s sake, let’s assume 10 printed circuit boards are manufactured, each with 100,000 interconnections.

For that lot of 10 printed circuit boards, there are 1,000,000 interconnections; 1,000,000 opportunities for failure within that lot.

In this simplified analogy, in a 6 sigma environment, four of the 1,000,000 interconnections could fail, as shown in Table 1. However, if the four interconnections are on individual printed circuit boards, it is possible 40% (4 of 10 circuit boards) would fail. This would be unacceptable in commercial markets, let alone high reliability markets such as medical, industrial, and military / defense electronics.
 

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Table 1

 

Quality levels

Sigma quality defects per million opportunities (DPMO) and percent yield

 

Ideally, customers, regardless of electronics end-market, would want their circuit boards to approach 6 sigma levels – four card failures per 1,000,000 boards. Which means the design, manufacturing, and supply chain functions must focus their quality to levels approaching 7 sigma – two defects per 100,000,000. (See: Improving SMT PCBA line productivity)

From an economic standpoint, improving quality to a 6 sigma level makes practical sense.

If an electronics manufacturer built one million circuit boards at 3 sigma levels, they would build 66,807 defective circuit boards.

Assuming each defective board required $100 worth of parts and labor to repair, it would cost $ 6,680,700 to complete the repairs.

Conversely, if such manufacturer was at a 6 sigma level, they would encounter four circuit board failures, which costing $400 – a 99% reduction in repair costs.

As Dr. W. Edwards Deming illustrated, if variation is reduced, there is no need to inspect manufactured items for defects, because there won’t be any.

In addition, due to the complexity of fine pitch electronics, inspecting in quality becomes impractical, even with automated inspection capabilities. Therefore, by reaching 6 sigma, variation in the product becomes minimum.

Therefore, there is no economic or technical excuse for not pursuing a 6 sigma level.

The next question is how to achieve such world class levels.

As illustrated in Figure 1, employing a 6 sigma methodology can result in improvements in quality, which results in a reduction of production costs. The basis of this DMAIC methodology consists of the following:

  1. Define: Identify and document the processes used to design and manufacture the product.
  2. Measure: Quantify the processes used design and manufacture the product. It is critical that process metrics be quantified. Quantitative metrics are metrics that can be measured and be independently verified.Quantitative measures are arrived at through analysis, surveys, economic data, environmental data, and efficiency data. Qualitative metrics are based on judgment and are subject to different responses from different decision makers.Qualitative research methods include anecdotes, interviews, observation, discussion, and directed inquiry.
  3. Analyze: Based on the process definition and measurements, areas for improvement are identified.
  4. Improve: The current processes will be optimized and implemented, based upon data analysis performed.
  5. Control: Upon implementation of the optimized processes, this step quantifies any improvements made to the processes and provides feedback on performance.

 

Figure 1

 

6 Sigma methodology

Six sigma five step methodology

 

As Figure 1 illustrates, 6 sigma methodology – DMAIC – is a continuous improvement process, where processes are constantly monitored and analyzed to identify opportunities for improvement and to successfully implement new techniques.

Continuous improvement comprises of a set of actions that transform an organization to a better state of performance.

Motorola was the pioneer in introducing 6 sigma methodologies to electronics manufacturing in the 1980s. By their account, Motorola estimates it has launched thousands of improvement projects for a savings of about $17 billion.

However, manufacturing process improvement is only part of the solution.

Hardware designs, as complex as they can be, must be producible.

A non-producible product can reduce overall quality levels. In many cases, the root cause of a quality problem is the lack of adherence to published industry design guidelines.

For example, a densely packaged design had a series of fine pitch ball grid array packages. These packages were soldered with a thermal profile which should have resulted in acceptable solder joints.
 

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When the process failed to produce a highly reliable product, the design and manufacturing processes were reviewed. It was determined a copper ground plane was designed into the circuit card directly under the fine pitch ball grid array packages, which reduced soldering temperatures sufficiently to result in a poor quality assembly.

Therefore, it is imperative all electronics manufactures achieve 6 sigma levels in their design and manufacturing processes. Failure to do so can result in loss of customers and a competitive edge in the global electronics manufacturing environment.

 

References

Qualitative Measures for Teams in Transition by Lunell Haught; Haught Strategies; Spokane, Washington; ASQ Annual Spring Conference Proceedings, Chicago, IL, Vol. 23, No. 0, March 2001

Mulbury Six Sigma

Motorola University 6 Sigma Dictionary

ISO/DIS 13053-1: Quantitative Methods in Process Improvement — Six Sigma — Part 1: DMAIC Methodology by International Organization for Standardization, 2010

Out of the Crisis by W. Edwards Deming; MIT Press

5 Issues Driving the Cost of Poor Quality by Tony Bellito; Circuits Assembly; August 2010




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