Printed Circuit Board Manufacture

The manufacture of a multi-layer circuit board typically starts with preparing the board laminates. Each laminate has a core of fiberglass-reinforced polymer resin, with both sides of the core laminated over with copper foil surfaces. The resulting laminate is then baked, to cure and stabilize the polymer core. Subsequent processing etches the copper surfaces, so that the copper circuit patterns are formed on each surface. After additional processing, the laminates are layered onto each other using isolation sheets, and fabricated into the multi-layer printed circuit board. Holes are then drilled through the board, according to the intended circuit design. After etching and deburring the drillholes, the board is electroless-plated with copper to deposit a conductive copper coating onto the wall of each drillhole. This conductive surface is then electroplated with copper, to strengthen and build up the copper surfaces on the drillhole walls. The purpose of the copper-coated drillhole walls is to connect the circuit pattern on each board laminate into a continuous circuit design among the laminated layers of the completed printed circuit board.

The copper-coated, multi-layered board then undergoes additional processing to complete the circuitry. Initially in this process, a dry film mask is applied onto the exposed copper surfaces on both sides of the board. The mask is applied as a pattern so that a circuit design is traced onto the copper surface. Subsequent processing exposes the copper tracings by removing the dry film mask according to the circuit design. The exposed copper tracings are plated with solder to protect the copper circuit. The mask is then stripped from the unplatted copper areas, which are then etched to remove any unsoldered copper strips. The ammoniacal etchant removes the unmasked copper, but does not remove the tin/lead solder plating that protects the copper circuit tracings. Then the panel is rinsed, and processed in 10% sulfuric acid as an oxidation inhibitor.

Wastestreams
For Circuit Board Manufacturers, the most prevalent hazardous wastestreams are spent aqueous process solutions, spent rinsewater, other metal-laden wastewaters, and the metalladen sludge that is precipitated by the treatment of the spent solutions, rinsewater, and other wastewaters. Many of the innovative source reduction measures listed here would reduce or eliminate sludge generation. Some of the measures would reduce the volume of aqueous wastestreams.

Source Reduction
Hazardous waste source reduction reduces or eliminates the quantity of hazardous waste generated at the source generating the waste. Source reduction can simplify and economize hazardous waste management.
Source reduction of process solutions includes several process substitution measures that reduce or eliminate the use of some process baths that generate hazardous waste. Some of the substitutions still do generate spent process solutions, but often at reduced volume, or as spent solutions that can be easily regenerated for reuse.

Recycling
Onsite and offsite recycling are a complement to source reduction. While source reduction avoids generation of waste at the source, recycling manages the waste to derive further benefit. Like source reduction, recycling is a preferable alternative to treatment or disposal of the waste. Recycling can recover spent process chemicals or rinsewaters. Recycling can also recover contaminants like copper and other etched metals. Like source reduction, recycling can reduce the risk and impact to human health and the environment. Recycling can reduce or delay the need for storage, handling, transport, and disposal of spent process chemicals.

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