I once saved up enough money for some exercise equipment at my local warehouse club store, only to be devastated to find out they no longer carried the product when I went in to buy it. That taught me not to rely on the expectation that something would always be there because I had seen it once on the shelf. Yet sadly, many PCB designers around the world are discovering this same bitter truth in their circuit board layouts. The parts they are expecting to use are no longer guaranteed to be available when they need them.
This component availability problem can be traced back to several reasons. In some cases, it is due to inadequate planning, while others are due to CAD library management issues that designers need to understand better. Here we will examine these potential problem areas and some good PCB design BOM inventory management practices.
Outdated CAD Components, How Can This Happen?
There are many reasons why a PCB design is created with outdated parts, starting with poor planning. As painful as it is to admit it, sometimes designers aren’t careful about which parts they choose. It is imperative to select parts based on current catalogs of availability instead of using the same old parts that have always worked in the past. It may be that those parts are obsolete or aren’t currently available. However, there are plenty of other reasons why outdated parts can sneak into a PCB database, and here are some of the more likely culprits:
Parts used from non-controlled sources
It is not unusual for designers to keep a cache of their favorite parts in personal folders and libraries. This private storage is understandable as the parts that have worked in the past, are in a known, easy-to-find location. The problem, of course, is that they are uncontrolled, and there isn’t any way to know if they are in compliance or not. Personal storage of library parts is a bad practice that should never be allowed in a PCB design group.
Outdated CAD library parts
Another prime source of outdated parts is CAD libraries that aren’t maintained. The design group should have a procedure in place for work-in-progress designs that call for the verification of its CAD library parts to a catalog of available parts. Without this level of control, it is possible that outdated parts that are obsolete or unavailable may find their way into a new design.
Copied circuitry
Outdated parts can also easily find their way into a design through copied circuitry. Designers often use circuitry on proven designs to start or augment new work. The risk is that without verifying the circuitry, it could contain many parts that are no longer available. Once again, the design group should have procedures in place to check for outdated parts and replace them. Next, we’ll look at some of the verification procedures in more detail.
Good Practices for PCB CAD BOM Inventory Management
The first step in establishing good practices for BOM inventory management in PCB CAD libraries is to develop a well-defined library process:
- Part requests: To build a new CAD part for PCB design should require a formalized request process. This request should be routed through component engineering to verify the application and availability of the requested part and confirm that the part conforms to company standards and policies.
- Manufacturing specifications: The parts’ datasheets should be kept on file within the design department and preferably within a product data management (PDM) system for access throughout design and manufacturing. This data will be used for the construction and the validation of the completed CAD models.
- Verification: The new part needs to be verified that it has been built correctly and satisfies the needs of all the key stakeholders (design, manufacturing, etc.). The verification sign-off should also be kept on file with the part request.
- Database updates: Once completed, the part needs to be installed in the library, and new part notifications published to the design team.
The next step of inventory management for PCB design teams is to establish the processes and procedures mentioned above for part updates and verifications in new designs. CAD library parts need to be confirmed in new designs as being the latest versions and available from the company’s supply chain. There also needs to be procedures in place to run the automated part checks through the CAD system on completed designs before they are sent out for manufacturing.
Finally, a very good practice to implement is the use of online PCB library services in the design of circuit boards. These services tie into part manufacturers and distributors, so you can rest assured that the symbols, footprints, and simulation models they provide will be up-to-date. Third-party PCB library services allow design groups to get right to work without worrying about the time, expense, and labor of maintaining a CAD library of PCB parts. You also have another resource that is helpful in BOM inventory management, and that is the resources of your local PCB contract manufacturer.
Getting Help to Manage Your PCB Bill of Materials
Contract manufacturers like VSE have a full staff of component and design engineers and procurement specialists that understand how to work within the electronic parts supply chain. By getting the data to your PCB CM early on in the design cycle, they can help you with BOM reviews for current parts and begin the sourcing process to know what is and isn’t available. At VSE, we have been helping our clients with this same process for over 35 years. Our commitment to working together with our clients has helped build our reputation as one of the highest quality-driven PCB contract manufacturers in Silicon Valley.
