Excerpt: The Evolving PCB NPI Process, Chapter 2


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Managing the BOM Handoff More Efficiently, Especially During Supply Chain Shortages
Managing the supply chain for electronics manufacturing has always been challenging. About 70-80% of the cost of building an electronic product is for the parts, while the remaining cost is in the process to assemble and test the product. However, during the worldwide pandemic, the strain on the overall supply chain for any product has been stretched to the breaking point. When supply of toilet paper, hand towels, and sanitizer is disrupted and cannot be found on the grocery store shelves, one could imagine the challenges in a similarly disrupted supply chain of efficiently acquiring complex electronic components. This situation further complicates the mBOM handoff between OEM PCB designers and their contract manufacturers, who are often in different countries and whose operations are also affected by component and materials shortages. 

Let’s look closer at the unique issues in delivery of design data from OEM to CM. The OEM creates a design package with the RFQ (request for quote) that is delivered to multiple CM companies. The OEM wants a competitive price from the CM they plan on using, so multiple bids are invited. 

From the CM’s perspective, they need to understand what the product is and how easy, or not, it will be to deliver an acceptable product to the OEM. The CM is expected to provide a bid to the OEM based on the BOM and production quantity needed. The CM will work up a quote, and, in most cases, will not be successful in getting the business. Many of the CM quotes are based purely on the mBOM file and a drawing of the expected product; in other words, they are not based on detailed evaluation of the design layout data, which makes it more difficult to provide a detailed, competitive bid.  

If we look further to the mBOM files created by the OEM, we essentially see a unique format from each OEM company. Sometimes, an OEM will send more than one format. Basically, these mBOM files describe the OEM’s part number, known as the customer part number (CPN), in addition to some form of part description. It likely includes a manufacturer part number (MPN), a list of the component names that correspond to each placement of the CPN, and quantity information that can be used to match the number of component names. 

To permit flexibility in part sourcing, particularly with the commodity passive and discrete parts, any CPN may have more than one possible MPN. This is known as an approved vendor list (AVL), which describes alternative parts that the CM can select from. These alternative parts are electrically equivalent to each other; however, there may be physical differences in the package that could impact the manufacturing process. These alternative part numbers could also be delivered through a list of approved manufacturer part data, which is known as an approved manufacturer list (AML). The mBOM file does not contain the MPN alternatives; instead, they are derived in a separate AML file. 

This all sounds straightforward, but the challenges for the CM stem from variations in the quality of this mBOM data. Particularly with prototype information, the data in the mBOM can be incomplete, difficult to read automatically, inconsistent, or just plain wrong. A lot of the OEM-supplied mBOM files look easy to understand to a human, but manually transcribing it into the CM system takes time and is fraught with the possibility of making data-entry mistakes. Text and Excel files are usually easy to read; however, the complexity comes from the format or structure of the file especially when the AVL data is included. 

Automation and Consistency are Critical
Being able to automatically import this data to the CM’s system is critical to efficiently processing the information. However, this step is more complex than it sounds. As we stated earlier, the OEM’s mBOM lists their part number, the CPN, and the MPN, all from the OEM’s perspective. The mBOM does not contain the part number that the CM uses, called the internal part number (IPN).

In the CM’s system, the IPN also maps to the MPN but they may not be a 100% match, or even close to each other. The ability of the CM to know what parts are available in their system already and what parts need to be purchased for the project is a critical step in the quoting process. The parts manufacturer names further complicate these connections. For example, consider Texas Instruments. We have seen this name in an OEM’s mBOM as Texas Instruments, Texas Instrument, Texas Inst, or TI. All these names mean the same thing, but if simple 1:1 matching is used, it may result in incorrect pricing up front or incorrect product assembly once the manufacturing process begins.

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