Page 151 - Six Sigma for electronics design and manufacturing

Six Sigma for Electronics Design and Manufacturing
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The information gathered from this example can be used by differ-
ent parts of the organization, helping them achieve their individual
goals. Management can use this information to document the produc-
tion lines progress toward six sigma. Test engineers can use this in-
formation to plan for test and troubleshooting stations. Production
and process engineers can use this information to focus on which
manufacturing operations most need quality improvements. In this
example, the ribbon bonding operation has the lowest Cpk and high-
est DPU, and therefore should be the first operation to be targeted for
quality improvements.
4.4 Determining Overall Product Testing Strategy
Ultimately, all defects have to be removed by testing the individual
assemblies that make up the product, and then finally testing the
product. Test engineers are concerned about the yield of the product,
in order to budget and plan for test and troubleshooting equipment
and operators. The six sigma quality defect rate and yield calculations
are excellent tools to help in the planning of electronic product test
strategy.
It is common knowledge in the test industry that the cost of inspect-
ing for and removing defects can be as high as 30% of the overall man-
ufacturing cost. In addition, the earlier a defect is caught and re-
moved in the manufacturing cycle, the cheaper it is in terms of
equipment cost and operator skills. The best alternative to expensive
test equipment and skilled operators is achieving six sigma quality
and the resultant assembly yield goals.
As shown in the examples in this chapter, the quality of the individ-
ual elements of an assembly can be linked to its total quality perform-
ance. In Example 4.2.3, 10 PCB assemblies, each with 95% test yield,
can result in the next level of assembly (final product made up of the
10 PCBs) having a yield of only 61%. If a higher yield for the next step
in the assembly is desired, then the yield of the individual compo-
nents have to be improved further.
In Example 4.3.2, it was shown that increasing the number of com-
ponents or steps in the assembly have a similar effect on reducing the
yield. The yield for an assembly of 90% based on 100 components or
steps quickly drops to 59% yield with 500 components, and then to
35% yield with 1000 components.
This combined effect of setting the yield goal and the number of the
underlying steps in the assembly operations have led test engineers
to examine the test strategy based on the ability of various test equip-
ment to remove certain level of defects.