Simple cost modeling for EPs: a continuation of last month's discussion of how to create an accurate, user-friendly methodology.

IN ORDER FOR the modeling tool to have reliable outputs, the tool designer would have to obtain reliable inputs from every IMS company, every embedded passive material supplier, every EMS company, and every discrete resistor and capacitor manufacturer. It would then be possible--but not necessarily practical--to create a reliable model Since the tool would probably be based on an ABC system, inputs from the manufacturers would have to be activity based. Assuming that the tool is built to this detail, then the tool user would have a dropdown menu with the following options:

** IMS company

* Several hundred choices

** Embedded passive material and supplier

* Dozens of choices and growing daily

** Discrete part manufacturer

* Dozens of choices

** EMS company

* Several hundred choices.

Once these selections are made, then models can be run. What are the odds of IMS, EMS and materials firms providing such inputs to the tool designer or the OEM if the tool is designed for the user to enter these data? What are the odds of anyone maintaining it? Everyday these costs change, for a variety of reasons. The tool would have to be maintained regularly to be reasonably accurate.

The desired results may be relatively easy to come by without the aid of a complex tool. Basically, you want to compare prices. What do you do? Already at your disposal are all the elements needed to produce the output of any cost modeling tool. These elements are:

** The BoM.

** A PCB designer who can provide an "if-then" analysis.

** An RFQ process for bare-board and assembly pricing.

Remember, what is really sought is a price comparison: If I do it this way or that way, how much will I pay? Regardless of the actual cost of embedding, the cost in this sense is the price paid for the board or assembly.

To make this comparison, you need to know just a few things about the PCB:

** The parts that can be embedded.

** The effect on the board size.

** The effect on the board materials and construction.

Even if the layout isn't complete, you know enough to analyze the costs: board size, specification, material, number of layers, copper weight, line width and space, finish, approximate number of vias, component holes and SMT pads. with this a quote can be obtained for the bare board. Similarly, from the same information plus the BoM, you can get a quote for the same quantities of assemblies. This will provide the baseline price without embedding.

Right on the heels of this, you can determine which parts to embed and which material technology to use for embedding. (See February's column, "When to Embed," for more on this topic.) Look for a large number of discrete parts with similar values and tolerances. These are candidates for embedding. Embedding these parts may of may not change the board size. However, the layer count probably will change, and the materials will change with the addition of the EP materials. To get price estimates, you will have to select the embedded passive material(s). There are many material choices for planar capacitances and even design techniques to create discrete capacitors within a planar capacitance structure. There are also material choices for discrete capacitors and these may be on the same layers as polymer thick-film (PTF) or ceramic thick-film (CTF) resistors. Similarly, there are many choices for resistors including metal thin films, PTF and CTF. Tolerances, trimming and other EP-related requirements will be known. This is enough information to take to the IMS and EMS companies for another quote. Do not overlook testing and trimming costs (the IMS will be responsible for these tasks). Be clear on your requirements. You now have enough information for a reasonable price comparison. The price of the conventional bare board plus discrete components plus assembly equals the basis price. The price of the embedded passive board, plus revised components plus revised assembly equals the embedded passive solution price.

You are the OEM project manager. You want a price comparison. Using the above simple methodology, it may take an hour to create a spreadsheet with the variables you want answered. It will take your designer a couple of hours to go through the "if/then" analysis and determine the affect on bare-board and assembly characteristics. Add another hour for you to tabulate and sketch inputs to give to your purchasing agent. Your PA burns up a couple more hours preparing and sending out RFQs and receiving pricing, tabulating it and transmitting it to you. You spend another hour digesting the data. Less than a week from idea to price comparison. Seven hours of management, engineering and PA labor in the process. Of course, this doesn't count the cost to the IMSs and EMSs to respond to your RFQ. But you don't have to worry about that.

There you have it, an accurate, user-friendly and timely cost comparison methodology. Be sure to save your spreadsheets, because as you build history, you are building your own models for future reference.

RICHARD SNOGREN is a member of the technical staff at Coretec Inc. (coretec-inc.com). He can be reached at [e-mail].