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Water Conservation Opportunities for
a Printed Circuit Board Manufacturer
Advance Circuits, Incorporated (ACI) is
a printed circuit board manufacturer with facilities in Minnetonka,
Hopkins and Roseville, Minnesota. The Roseville facility manufactures
multilayer circuit boards for products such as pagers, cellular
phones and personal computers.
The multilayered circuit boards
manufactured by ACI consist of alternating layers of conducting
and insulating material that are bonded together. The layers
are connected with plated-through holes.
During the manufacturing process,
the circuit boards undergo numerous production steps, including:
creating circuitry for individual inner layers; optically
inspecting those circuits; laminating inner layers together
into hardboards; drilling, deburring, desmearing and electroless
copper plating of holes in the hardboards; pattern plating
the outer sides of the hardboards; soldermasking; soldering;
testing the circuitry for electrical integrity; and visually
inspecting final products before shipping.
At the ACI Roseville facility,
water is consumed at a rate of approximately 470,000 gallons
a day. Water is used to prepare process chemical baths and
for rinsing off soils and residues from boards in both immersion
baths and enclosed spray cabinets. Soils and residues include:
pumice and alkaline cleaners; copper etchants; catalysts;
plating solutions; sensitizers; and wet- and dry-film photoresists,
solvents, developers and strippers.
Incentives
for Change
Currently, ACI is in the process of expanding its operations,
which will significantly increase its demand for more water.
However, this increased need for water will exceed the capacity
available from the City of Roseville. In addition, sewer accessibility
charges (SAC) are expected to increase from the current charge
of $800 per SAC unit (274 gallons per day) to $850 per SAC
unit. SAC assessments are made every three years to fund wastewater
capital improvement projects in the sewer district. (Note:
current cost to use and sewer the city water is $3.46 per
1,000 gallons.)
The goal of the intern project
was to find opportunities to conserve water in order to reduce
ACI's need for additional water and its associated costs.
Intern
Activities
The intern began by researching the processes of manufacturing
multilayer printed circuits and how water was used at the
facility. He assessed the production operation by observing
ACI's operating procedures; measuring or estimating water
use and pressure (when possible); and inspecting items such
as tanks, enclosed cabinet chambers, pumps, pipes, spray nozzles,
sumps and photo sensors. Water flow rates and pressures for
each process were recorded.
One of the initial tasks of
the project was to determine the cleanliness of the boards
at each step of the process. However, due to limits on time
and other factors, the intern instead concentrated on finding
ways to conserve water by optimizing processes and equipment.
After evaluating rinsewater
flow for eight weeks, the intern made a number of suggestions
to ACI process managers and engineers. These suggestions are
summarized below.
Project
Results
Flow Rates. Baseline measurements of water flow rates
revealed that several parallel process lines (used to produce
identical products using identical processes) had different
rates of water flow. The intern suggested to ACI that if the
process lines that used less water produced boards of acceptable
quality, then the process lines that used more water could
be operated at a reduced flow rate that matched that of the
lower flow line.
Flow Gauges. Another
suggestion was to install flow gauges to monitor water flow
in additional locations throughout the plant. Knowing the
flow rates of water-supply lines for each process would allow
ACI to better quantify flow rate reductions and calculate
water and cost savings.
Photosensors. Restricting the rate of water flow at ACI has been done primarily through the use of photosensors. A photosensor is an electronic "eye" that can "see" a board as it passes by, which activates a timing device connected to a solenoid valve that turns water on and off (either flow or spray). The intern made the following suggestions to optimize the use of photosensors:
- repair or replace defective photosensors;
- perform routine maintenance (clean and readjust) to keep them in good working order.
- decrease the duration of the rinse time to limit the amount of water used to only what is necessary for rinsing; and
- install photosensors in spray rinse chambers where they do not exist.
Housekeeping. The following general housekeeping measures were suggested by the intern:
- eliminate hoses that supplement supply water to spray rinses;
- hard plumb all water-bearing supply pipes;
- improve the movement of water use in spray cabinet sumps and immersion baths to maximize the rinsing capabilities of the water; and
- recirculate freshwater rinse to an earlier rinsing stage using a counterflow method, or reuse it as make-up water for process bath or spray solutions.
Cleanliness Standards.
Another suggestion by the intern for ACI was to develop a
cleanliness standard for boards at every stage of the process,
making it quantitative if at all possible. Then the minimum
amount of water needed for rinsing boards to achieve this
standard could be determined.
Conclusions
Though specific cleanliness criteria for boards were not established,
ACI implemented most of the good housekeeping and flow rate
reducing suggestions, which should significantly reduce water
use. Estimated capital costs for purchasing suggested equipment
would total under $1,700. Estimated reduced water use from
implementing these suggestions would total over 52,000 gallons
per day, or 18.3 million gallons annually, resulting in an
estimated cost savings of $63,000 per year. If the SAC is
included in the savings estimate, the total cost savings would
be approximately $225,000 the first year.
In addition to implementing
many of the intern's suggestions, ACI is incorporating a water
reuse system into its expansion plan to further reduce water
consumption.
More
Information
If you would like more information
about this intern project or about the MnTAP intern program,
call MnTAP at 612.624.1300 or 800.247.0015 if
calling from greater Minnesota.
This
project was conducted in 1994 by MnTAP intern Scott Schingen,
a chemical engineering student at the University of Minnesota.
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