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Case Study 9 - Flexible Simulation Modeling of PWB Costs

Printed Wiring Board
This bulletin highlights the following pollution Prevention Work Practices:
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Even if you have carefully researched how certain changes in your production process may affect your costs, it can still be difficult to anticipate the effects of all possible changes. The environmental costs, such as generation of waste, treatment of waste, water and electricity use, can be particularly hard to anticipate. Wouldn't it be nice to have a crystal ball to predict the effects of changes on your processes and production? The Flexible Simulation Model, developed by the Industrial Engineering Simulation Laboratory (IESL) at the University of Tennessee in conjunction with the EPA's DfE Program, can show you how modifications in your production process will affect your costs.

Find Savings by Finding All Costs

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Traditional cost analyses look only at the direct costs of making a change to a process or product. Direct costs include capital expenditures, labor, and materials. Some PWB facilities allocate costs associated with air emissions, wastewater, and solid/hazardous wastes to "indirect costs" or "overhead." But no longer! When you are estimating costs for new equipment, new products, or any other process change, it is important to fully consider both direct and indirect costs, including handling of the wastes you will generate.

By allocating waste handling and other environmental costs to the specific processes from which they originate, you can identify more precisely how much it will cost to run the process.

Knowing this information before you embark on a change in your operations will help you configure the optimal process design to keep your expenses as low as possible while reducing your facility's impact on the environment.

Alternative Accounting Methods

Alternative accounting methods attempt to improve upon traditional costing by including indirect costs as well as direct costs, and by allocating indirect costs to the products or processes that actually drive those costs. However, these methods may require extensive data input, which can be so time-consuming that it is not always practical.

Simulation modeling makes the process of assessing costs much simpler. Simulation duplicates production processes on a computer, allowing users to experiment with different scenarios without disrupting production or incurring any of the costs of actual implementation. Since simulation models duplicate production processes, they allow tracking of specific activities that otherwise would be aggregated into overhead costs. These models can be designed to allow the user to try out any number of variables, such as the number and type of operations, the sequence of operations, production volumes, and process times.

Some simulation models have been criticized for lack of flexibility and applicability to the real world - in this case, to printed wiring board (PWB) manufacturing. In order to design a generic "model" process that represents a typical or standard process, software developers must make numerous assumptions - about the sequence and timing of process steps, the chemistries used, the facility's operating hours, even the physical size of tanks and equipment. PWB manufacturers contend that an "average" facility is rarely representative of any real operation, because there is such diversity in processes from one facility to the next.

The Flexible Simulation Model

The Flexible Simulation Model, which was developed for PWB manufacturers, allows facility staff to input the parameters of their own particular production process. These inputs will convert a standard process into one that is unique to the facility being evaluated.

The Flexible Simulation Model has a number of benefits for PWB manufacturers:

  • The model is a powerful tool to help you estimate the impact of process changes on a facility's costs and production metrics, such as throughput time, inventory, and scrap.

  • It provides a better understanding of total costs, which can help you identify areas where you can reduce wastes and inefficiencies to save money.

  • It allocates all costs directly to the specific processes from which they originate, so you can see exactly how any change you might make would affect other aspects of your operation.

  • It enables you to evaluate the costs and savings of switching to a new process in your facility - before you purchase equipment or disrupt production.

  • Even if you have no knowledge of computer modeling, the model allows you to experiment easily with different processes that are specific to your facility and its particular needs.

To use the Flexible Simulation Model, a user first enters production data and parameters (e.g., cycle time, volume of chemicals used, frequency of bath additions). It is important to realize that although this model can produce powerful facility-specific results, good inputs from production management and process engineering are essential to producing accurate, reliable results. Once the facility-specific information is entered and a specific number of boards are requested to be "run," the simulation program "produces" the boards. The model then creates profiles for cost, production, and environmental aspects of the PWB operation. To date, the model has been run for the plating through-holes process. It can be easily adapted to model any wet chemistry process.

Validating the Flexible Simulation Model

Before the new model could be considered reliable by PWB manufacturers, it had to be validated. The validation process confirms that the model generates results that reflect the actual world of PWB manufacturers. To collect the data needed to validate the model, a team from the IESL made a two-day site visit to ITO Industries in Bristol, Wisconsin. ITO Industries manufactures PWBs for the medical, telecommunications, and building safety device industries. ITO operates three shifts per day, with over 60 production employees.

The validation compared the cost, production, and environmental profiles generated by the model to the known costs tracked by ITO Industries. To simplify the validation, the team focused on one process line, the direct metallization of through-holes. The validation involved three phases:

  • Simulation validation: The model estimated the amount of labor, time, water, chemicals, and other inputs required to produce 350,000 surface square feet (ssf) of boards. ITO verified that these numbers were accurate, thereby validating the process simulation.

  • Cost validation: The model estimated the resulting cost/ssf for the direct metallization line to be $0.26/ssf. This cost was compared to ITO's in-house estimate, which was calculated manually as $0.20-0.30/ssf.

  • Comparison to a static model: The University of Tennessee team also compared the cost generated by the model to their own manual estimate, which also was $0.26/ssf.

The consistency of these results validates the model for the process of making holes conductive.

To Model or Not to Model?

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The Flexible Simulation Model uses ARENA 3.0 simulation software. Running the model yourself in your facility requires having both the model and the software to run it. This option can be especially useful if you have a large facility with many choices to make. If your company is interested in using the Flexible Simulation Model, you may purchase the ARENA simulation software, obtain the model at no cost from the University of Tennessee, and run as many scenarios as you choose. (The ARENA software retails for approximately $16,000.) Alternatively, you may have the IESL at the University of Tennessee analyze your data for you, for a nominal fee. Depending on the process, fees are expected to range from $250 to $2,500.

The Real Costs of Doing Business

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Whether or not you decide to use a modeling simulation program, the concepts behind the model are always important to consider when you estimate costs for your PWB operations. The chart on the facing page lists the major categories of costs that you should think about when thinking about making a change to your operation. Within each category, you may want to include other items that are specific to your business. Similarly, some of the items listed may not apply to your operation.

Careful consideration of all the costs that a change in process could generate is just smart business. By considering environmental costs and impacts in addition to performance and other product costs, you will obtain a much more complete and accurate picture of the full impact on your operation of any potential change. This knowledge will help you to reduce your expenses and remain more competitive, while decreasing the environmental impact of your work. Once you begin taking environment costs into account, you may be able to identify ways to operate your business more efficiently.

Cost Categories to Consider Before Making Changes to PWB Operations

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These are general categories, and not every item will be relevant to your business. However, every cost in your facility should be allocated to one or more specific operational areas, rather than being tucked away in a separate category such as "overhead." An item is sometimes listed in more than one location, because it may apply to several categories (e.g., purchasing water treatment equipment would be relevant to both Capital Costs and Wastewater Costs).

Capital Costs

  • Equipment purchase and installation
  • Purchase of buildings and/or property
  • Project engineering, site preparation
  • Labor for planning, preparation, installation

Material Costs

  • Chemicals
  • Personal protective equipment
  • Other supplies

Maintenance Costs

  • Bath setup
  • Sampling and analysis of bath chemicals
  • Filter/membrane replacement
  • Tank cleanup
  • Labor for maintaining equipment and bath chemistry

Other Production Costs
These costs will depend on the specifics of your operation. Categories to consider may include the following:

  • Transportation of material within facility
  • Labor for line operation
  • Time needed to produce desired output of boards (including ssf/hr)
  • Down time (for breakage, equipment malfunctioning, bath replacement time, etc.)
  • Quality cost (scrap)

General Facility Costs

  • Utilities (water, sewer, electricity, natural gas, oil, solar)
  • Rent

Air Emissions Costs

  • Control equipment
  • Labor (for tracking, monitoring, reporting, maintaining equipment, etc.)
  • Permits, fees

Wastewater Costs

  • Treatment chemicals
  • Treatment equipment
  • Labor costs (for on-site water treatment, etc.)
  • Permits, fees

Solid Waste Costs

  • Management of solid waste on-site
  • Transportation equipment
  • Transport of waste off-site
  • Permits, fees
  • Labor (for monitoring, completing waste manifest paperwork, handling solid waste, etc.)

Training, Supervision, and Management1

  • Salaries and benefits
  • Supplies and materials

Potential and Actual Liability Costs1

  • Penalties and fines for unallowed/excess emissions
  • Personal injury and property damage
  • Costs of litigation or of mediation with community, other businesses, etc.
  • Corporate/business image to community, investors, lenders, regulatory groups, etc.

1These categories are not included in the Flexible Simulation Model.


EPA's Design for the Environment Program would like to thank ITO Industries and the University of Tennessee for participating in this case study.

For More Information

To have the University of Tennessee run the PWB model for a specific scenario, or to obtain the Flexible Simulation Model for use in your own facility, please contact Dr. Rupy Sawhney at the University of Tennessee, Department of Industrial Engineering, Industrial Engineering Simulation Laboratory:

Telephone: 423-974-3333
Fax: 423-974-0588

Design for the Environment Printed Wiring Board Project

Through the Design for the Environment (DfE) Printed Wiring Board (PWB) Project, representatives of the PWB industry and other interested parties formed a partnership with the U.S. Environmental Protection Agency (EPA). This project is a voluntary, cooperative, effort in which EPA and its partners are working together to develop technical information on pollution prevention technologies and practices specific to the PWB industry.

The DfE PWB Project has conducted two comprehensive evaluations for the PWB industry, which are called Cleaner Technologies Substitutes Assessments, or CTSAs: The topics of the CTSAs are:

  1. Alternative Technologies for Making Holes Conductive (completed)
  2. Surface Finish Alternatives to the Hot Air Solder-leveling Process (in progress)

These evaluations enable PWB manufacturers to make informed business decisions that consider human health and environmental risks, as well as performance and cost.

The DfE PWB Project has also developed other case studies that examine pollution prevention opportunities for the PWB industry. All case studies are based on the experiences of facilities in implementing pollution prevention initiatives. You can read and download the case studies and the Making Holes Conductive CTSA from the DfE website, at:


You can also order documents from:

Pollution Prevention Information Clearinghouse (PPIC)
1200 Pennsylvania Ave. NW (7407-T)
Washington, DC 20460-0001
Phone: 202-566-0799
FAX: 202-566-0794
E-mail: PPIC@epa.gov

The DfE Program welcomes your feedback. If you have implemented any of the ideas in this series of PWB case studies, please tell us about it by calling the DfE Program at 202-260-1678, or via E-mail: oppt.dfe@epa.gov.

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