1996 Electronics Industry Environmental Roadmap - Civil and ...

Emerging Technologies
Outerlayer Processing: Outerlayer processing represents the final major process step to
complete a multilayer circuit board. Through-hole plating adds metal not only to the hole
walls themselves, but also to the outer layers of the laminated innerlayer cores. These exterior
surfaces must ultimately be patterned to provide the necessary connections for
circuit components later added to the PWB. Most PWB outerlayers are produced through
a subtractive process, in which copper is selectively removed from the plated PWB to
form a circuit [35]. Semi-additive or fully-additive processing, in which the manufacturer
forms the copper image by selectively plating copper onto the substrate, are alternative
outerlayer processes emerging in the manufacturing base. Improvement of additive metal
deposition technology, according to the IPC, requires higher precision, consistency in
resolution, and demands a focused program of research for new equipment, processes,
and infrastructure [36].
Figures 6-3 through 6-4 summarizes the overall multilayering process including lamination, drilling,
and outerlayer processing. Subtractive, semi-additive, and fully-additive techniques for
outerlayer processing are detailed.
Final Surface Preparation: Numerous surface finishes are possible once all copper
circuitry has been patterned on the PWB. Depending on the component assembly
processes to be used on the circuit board, gold, solder, or bare copper (with a anti-tarnish
coating) are possible. In one common process termed hot-air solder leveling (HASL), the
panel is dipped into molten solder, and then blasted with hot air to even out the solder
coating on which customers will mount parts.
Environmental Impacts: PWB manufacturing is a complicated process and includes
several steps that use significant quantities of chemicals and metals. On average, the
waste stream constitutes 92%—and the final product just 8%—of the total weight of the
materials used in the PWB production process. Approximately 80% of the waste
produced is hazardous [37], and most of the waste is aqueous, including a range of
hazardous chemicals. Table 6-3 illustrates some example environmental issues resulting
from the more common process steps as outlined above.
Process Environmental Issues/Impact
Base material manufacturing Chemical waste stream from copper foil
manufacturing, resin production
Lamination Energy consumption
Drilling Solid waste products from drilling
Desmear Chemical and/or gaseous waste from etchback of
drilled PWB
Through hole/outerlayer plating Chemical waste from electrolytic and electroless
copper baths
Resist develop Chemical waste from dissolved resist and spent
developer
Resist strip Chemical waste from dissolved resist and spent
stripper
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