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?

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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.

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.

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