Page 219 - Six Sigma for electronics design and manufacturing

Six Sigma for Electronics Design and Manufacturing
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plated on the raw PCB only to be removed at subsequent processes.
This includes the bulk of the copper plated on the original laminate.
Additive elements of the PCB have typically been restricted to metal
plating operations and outside layer dielectric solder mask. Acid cop-
per and electroless plating operations used in PCB fabrication utilize
large amounts of wet chemistry. This chemistry is costly to the fabri-
cator due to both the process control and effluent waste treatment re-
quired.
A fully additive process capable of achieving the desired electrical
properties of raw PCBs without the use of wet chemistries could po-
tentially reduce the PCB fabrication cost by reducing the costs associ-
ated with extra processing and waste management.
Additive processes will continue to become more prevalent in the
future of the PCB fabrication industry. Currently, standard etching
operations continue to decrease line width and space between the
lines down to 2 mils. The critical limitation of the lines and spaces is
the metal etching operation, which removes material in an isotropic
manner.
Electronic component designs continue to become smaller with ad-
ditional electrical performance requirements. This is driving design-
ers and PCB fabricators to incorporate many electrical elements of
the finished assembly into the raw PCB itself, either on the surface or
buried within the layers. The passive components, such as resistors
and capacitors, are beginning to be designed as buried elements with-
in the PCB.
An additive technology that appears to hold great promise as a sig-
nificant contributor to the future of raw PCB fabrication is polymer
thick film (PTF). PTF is an attractive technology because it is fully
additive and produces very little waste. The technology is also very
easily processed. Typical applications use simple screen printing oper-
ations followed by a drying step. The drying step is generally done at
temperatures comparable to that of current solder mask cures. The
PCB fabrication industry is already very familiar with screen printing
operations for both solder masking and legend printing. Most fabrica-
tors already possess both the equipment and general background to
process PTF technology.
PTF technology can be used for applications that include both fully
additive circuits and configurations that use a mixture of etched or
plated copper in conjunction with PTF PCB features. PTF is already
widely used for applications that include jumper circuits for product
revision changes, precious metal plating replacements for switch ap-
plications, electrical shielding, and both surface and buried resistor
configurations. Silver through-hole and via connections using PTF are
very popular practices that are used in Europe and are gaining use in