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.
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.
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.
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.