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Comprehensive Item Master & Related BOM Item Structure

The Item Master, sometimes referred to as the Part Master, is at the very core of the company enterprise management system, but more often than not it contains only listings of component parts and part-based assemblies. By limiting the Item Master to hardware components only, there are significant lost opportunities for cost accounting and correct revision build verification.

For maximum benefit, the Item Master must contain all of the numbering assignments and descriptive and accounting data for every item the company buys, sells, produces, supports, and maintains. This not only includes parts or components, but also numbered assignments for user manuals, warranty cards, installation kits, marketing brochures, software and firmware programs, training manuals, company procedures, shipping materials, inside and outside labor, mechanical drawings, schematics, silkscreen artwork, and basically anything else the company has assigned a value to and wants to track as an inventory, non-inventory, direct or indirect Labor, or outside services type with a location with a standard cost (indicating where it is used, and at what revision). Here is an example of how all of these various items may fit into a process or a bill of materials (BOM).

Beginning with a specific numbered and revision schematic and a subsequent set of Gerbers, we can now fabricate a bare printed-circuit-board. For the sake of example, let's construct a simple indented BOM:

    010-00001-001 = Bare PCB
    S010-00001-001 = Represents the schematic
    C010-00001-001 = Represents the CAD or Gerber Files

Now let's go back to the Item Master and examine the assembled PCBA and modify our BOM to nested version:

    021-00001-001 = Populated printed circuit board assembly
    010-00001-001 = Same bare PCB
    S010-00001-001 = Represents the schematic
    C010-00001-001 = Represents the CAD or Gerber Files
    028-00004-001 = Crystal of a specific value
    030-00008-001 = Switch of a specific value
    042-00010-001 = Resistor of a specific value
    800-00001-001 = Outside assembly labor

Now we have a small printed circuit assembly populated with components and included in the BOM — at the same level as the components is the assembly labor cost for the specific board being assembled. This labor cost is picked up from the assembly house quote and included in the Item Master. Now when the cost of a printed circuit card is tallied, the labor is a “component” of the cost. Now we continue to build a higher-level assembly, and this time we will include revision indicators:

    021-00001-001 Rev 2B = Populated printed circuit board assembly
    010-00001-001 Rev 2B = Same bare PCB
    S010-00001-001 Rev B = Represents the schematic
    C010-00001-001 Rev B = Represents the CAD or Gerber files
    012-00007-001 Rev A = Metal bracket with insert Grommet
    012-00007-000 Rev A = Bracket without Grommet
    011-00001-001 = .25″ O.D. Grommet
    W500-00000-001 Rev A = Work instruction document for attaching the Grommet
    028-00004-001 = Crystal of a specific value
    030-00008-001 = Switch of a specific value
    042-00010-001 = Resistor of a specific value
    800-00001-001 = Outside labor

Now our assembly has grown to include a bracket. In order to build the bracket, it had its own sub assembly, including a work instruction on how to affix the grommet to the bracket. We have this work instruction under revision control so when we order the PCBA from the assembly house, they can retrieve the latest revision of the instruction as it shows on the BOM.

Let's take it up a notch higher to an electromechanical sub assembly that incorporates the PCBA, and an RF shield over the crystal:

    131-00004-001= Electromechanical sub-assembly with sheet metal with silkscreen pin indicators
    012-00009-002 Rev B = silkscreened shield
    012-00009-001 Rev B = shield without silkscreen
    A012-00009-001 Rev A = silkscreen artwork under Revision Control
    D012-00009-001 Rev B Mechanical drawing for shield fabrication
    021-00001-001 Rev 2B = Populated printed circuit board assembly
    010-00001-001 Rev 2B = Same bare PCB
    S010-00001-001 Rev B = Represents the schematic
    C010-00001-001 Rev B = Represents the CAD or Gerber files
    012-00007-001 = Metal Bracket with insert grommet
    012-00007-000 = Bracket without Grommet
    011-00001-001 = .25″ O.D. Grommet
    W500-00000-001 Rev A = Work instruction document for attaching the Grommet
    028-00004-001 = Crystal of a specific value
    030-00008-001 = Switch of a specific value
    042-00010-001 = Resistor of a specific value
    800-00001-001 = Outside labor

Now if we want to order a shield, we call our fab house and order a 012-00009-002 Rev B and give them the Artwork REV A and the Drawing Rev B each time we order. We do not leave it up to the fab house to retrieve previously used documents. We order the part and include the new documents with revisions reflecting exactly what we want the house to build.

If we go up another level to a final assembly, we include the drawings for the enclosure, silkscreen artwork, fasteners, etc. Finally we go to a Finished Goods Level (FG) or Top Level Assembly (TLA) and our BOM includes the shipping carton, install kits, documentation to include in the packaging, and any other item that requires cost accounting and becomes a factor in the Cost of Goods Category on Finance's Chart of Accounts.

The benefit is huge if we include all these items in the Item Master. Now when your forecast is to build 150 of a TLA, your MRP system quickly tallies your total cost including all the labor for outside assembly, direct labor for inside assembly and testing, and packaging. Also, if all the procedures and work instructions are on the BOM, then the factory line is using the latest instructions to properly produce this product.

The Item Master is where you will get the biggest bang for your buck if you manage it properly. If drawings, procedures, and work instructions are checked in and out of Documentation Control and match up with the Rev level indicated on the BOMs, you will have the least amount of unanticipated and unpleasant surprises on the factory floor.

For each Item, at a minimum, the following should be entered into the Part Master System:

  • Your company part number
  • The revision number or letter
  • Type (part/assembly/inventory/non-inventory/labor — inside/labor outside
  • Standard cost
  • Manufacturer's name
  • Manufacturer's part number
  • Alternate manufacturer's name
  • Alternate manufacturer's part number
  • Make vs. buy (Make part will have a drawing)
  • F.I.T. (reliability number)
  • An attached purchasing specification document, supplier datasheet, company document, technical drawing (no Rev)

The Item Master must be maintained to ensure absolute integrity as almost every department in the company can be affected if the wrong revision of a product is made or a wrong part number is soldered to a 150 board. Imagine what would happen if a bench technician programmed 3000 serial proms with an outdated version of the software simply because he couldn't go online and query the BOM for the software's part number and revise for the latest build requirement.

More than once, I have seen a source code pulled from a bench computer because the technician thought he had the latest version on his system. Again, I cannot overstress the value of proper documentation control, and the Item Master is where it all comes together.

8 comments on “Comprehensive Item Master & Related BOM Item Structure

  1. _hm
    November 9, 2011

    This is good for large organization. However, it needs significant man power and time. If you work in design department, most of work finally ends up with design engineer. How can we find a way to implement this procedures without invoving design engineers?

     

  2. mario8a
    November 9, 2011

    Hello 

    I might lost track of the purpose of the article, just by reading I got confuse about how comprehensive should be, to my it looks cumbersome.

    Perhaps is because I'm used to XXXXX-XX and managing the Rev level within the DWG structure.

  3. jbond
    November 10, 2011

    @_HM

    I agree with you that this works great with a large company. Some smaller companies would have issues with the time and money it would take to implement a system like this.

  4. ThinkNThanks
    November 10, 2011

    I think the focus of this post is on Cost Saving strategies. At time, the organizations try to drive for cost reduction on the products, they only aim at DE and CM levels but did not focus on Documents Control. I think the DE doesn’t have to drive the process, it is not their function anyway, but the expectation is DE has to work in detail with Document Control to implement the process. We all know “garbage in is garbage out”, that why can’t throw the Document Control out of the Cost Saving Plan or deliver the great products. I think this should be done at any small or large size of organization.

  5. stochastic excursion
    November 10, 2011

    The benefits of a comprehensive item master depend more on where the product is in its lifecycle no matter what the size of the organization.  Generally the further a product is out of R&D, the more beneficial a stable BOM is.  Peripheral items, such as documents and the contents of flash memory, benefit from an item master that can be accessed and administered by both product management and marketing.

  6. _hm
    November 10, 2011

    Cost of making very good docuemntation and bullet proof products are very high. If customer is ready to pay for this price, company can perform it. However, customer is so short of money, it is difficult to justify very complete documentation and quality.

     

  7. dalexander
    November 10, 2011

    ThinkNThanks has identified the crux of the material presented. I also share the sentiment that this looks cumbersome, however, if I may suggest, cumbersome implies problematic in much the same way an overstuffed suitcase may be heavy, but when you get to where you are going, you have everything you need and you don't have to make extra trips to the store, interrupting your planned get-away, and changing your schedule. In fact, I am working on a prototype build first board, first BOM, and I am adding all the things we talked about right up front. On another level, this level of documentation lends itself to configurable BOMs quite ideally. Highly optioned products using a configurable BOM front end becomes as easy as picking items off the store shelf and dropping them in your shopping cart. I suspect Dell Computers are configured, assembled, and packaged in just this manner. In short, doing all the heavy lifting up front, builds muscle into the whole company and allows significant time and effort savings when the company's volumes and schedules are becoming more critical when the bulk of the effort needs to be focused on manufacturing and not documentation. Documentation Control pays for itself in a very short time because the long-term efficiencies gained more than cover the extended investment up front.

  8. dalexander
    November 10, 2011

    Mario8a, the second page brings it all together. The Design Engineer has a huge responsibility at every step of the design stage right on through Sustaining Engineering. That means after the handoff to manufacturing, the documentation should be as self explanatory as possible so there is a complete audit trail for every ECO/ECN with the DE's authorizing signature. Suppose as a DE, you were not allowed imput into the operator's manual or troubleshooting guide because they were not under Document or Revision control. Now imagine, you wrote the first guide and someone changed it without your knowledge. If there is a problem in the field with the integrity of the guide, it will be considered your problem because your name is on it. But, if you had to authorize any changes and bump the revision to match the latest BOM build, the blame game won't even get started and more importantly, the customer has the right troubleshooting guide for the correct BOM build.

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