Page 214 - Six Sigma for electronics design and manufacturing

Six Sigma Quality and Manufacturing Costs of Electronics Products
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The quality loss function can also be used to find an optimum level
of quality at which the target factory quality can be balanced by the
customer dissatisfaction of escaping potential defects. This would im-
ply balancing the product shipping tolerance at $100 per defect re-
moval at the factory versus the advertised specifications (±6mm) with
a defect removal of $500 at the customer site. This can be shown
mathematically as follows:
A
A
L factory = L customer =
2
2
factory · MSD = · MSD (6.4)
customer
100 500
=
2
2
factory 6
factory = 3 6 0 0 /5 0 0 = ±2.68 mm shipping tolerance
The above calculations indicate that the factory should set the tol-
erance of the manufacturing process at ±2.68 mm with a $100 cost per
defect in order to balance the customer tolerance of ±6 mm and $500
cost per defect.
It can be seen that this methodology can provide an alternate ap-
proach to six sigma is setting product specifications based on the
trade-offs of removing defects at various points in the product life cy-
cle. This analysis is similar to the one performed for testing strategy
in Chapter 4. Obviously, the quality loss function methodology is diffi-
cult to quantify, especially since the customer defect cost, as ex-
pressed in terms of loss to society, is difficult to ascertain.
6.2.3 A practical quality and cost approach
Both six sigma and the quality loss function discussed above are use-
ful tools that can be used to achieve an assessment of product quality
in design and manufacturing and relate it to the cost of the product.
For six sigma, the connectivity to cost is that the desired quality
target of 3.4 PPM is required by customers to maintain a high level of
growth enjoyed by electronics companies such as Motorola. There is
no volume adjustment to the six sigma philosophy, so that the quality
level is expected to be the same for mass-produced items such as cel-
lular phones and pagers as for low-volume products such as those
used by aerospace and the military.
The quality loss function (QLF) can be used as comparative esti-
mate of the loss to the product incurred because of its process average
shift versus target or its variability. It can also be used to measure
the trade-off of quality between the factory and the customer, as
shown in the example above (Section 6.2.2). The cost of a potential de-