Page 220 - Six Sigma for electronics design and manufacturing

187
Six Sigma Quality and Manufacturing Costs of Electronics Products
the United States. Fabricators of simpler raw PCBs can deposit
switching configurations and through-hole connections in a single
printing pass. Inks are being used as part of filled via hole configura-
tions to add hole wall integrity to the via as well as remove heat from
high-density packages such as ball grid arrays (BGAs). These filled
via connections can be used as part of buried via configurations for se-
quential and nonsequential configurations that utilize tag drilling.
Although fully additive circuits are currently possible using PTF
inks, the application has generally been limited to low-power switch-
ing operations. The finished circuit trace consists of metal flakes en-
capsulated in a polymer binder. A nonhomogenous conductor is creat-
ed by contact between adjacent flake material. Unfortunately, even
the most conductive PTFs currently have line resistance values that
are considerably higher than an etched circuit. The line resistance
tends to attenuate electronic signals and produce line resistance.
Dimensional limitations have also hampered the widespread use of
PTF products for fully additive circuitry. Typical PTF line widths and
spaces are 10–20 mils. Current etched cooper line widths and spaces
are significantly tighter, generally in the 4–6 mil range and as low as
2 mils.
In its current state, PTF additive circuits cannot become a replace-
ment for high-power etched copper raw PCBs. If the line resistance
and dimensional problems can be overcome, fabricators could benefit
from the savings accorded to a “greener” method of manufacturing
printed circuit boards. In the interim, PTF’s versatility for specialized
applications should continue to provide PCB designers with good solu-
tions to today’s complex electronic circuit designs.
6.3.3 Printed circuit board (PCB) design, fabrication,
cost, and quality issues
The PCB manufacturing process is not standard and is heavily de-
pendent on design parameters. A low-component-density PCB could
be implemented in a two-sided (two-layer) fabricated PCB, which does
not require inner-layer processing or lamination. Similarly, many fab-
ricators use inner-layer inspection only for very dense or controlled
impedance designs. The type of solder mask selected (screened, dry
film, or liquid photoimageable) is dependent on the density of signal
lines and the types of assembly requirements for the PCBs.
The operating cost of a manufacturing facility will include overhead
for administration and marketing. However, these are usually applied
evenly across all products and are therefore not design-dependent.
By examining the list of cost factors, the PCB features that affect
the cost of the design can be identified. The number of layers will de-