It always helps to start with an ingredient list before shopping. When the only options are multiple trips to the store or buying extra (and figuring out what to do with the excess), a more measured approach to taking inventory prevents purchasing too much or too little. Lest you want to end up with a spice rack that looks like it belongs to a doomsday prepper (guilty), it takes little time to evaluate how much of an item is available and necessary.
Planning purchases is essential when designing a circuit board but to a much more meticulous degree. While the build-up of components and foundries worldwide continues to grow for future demand, the current component supply chain is still experiencing lengthy lead times on many fundamental circuit elements. Creating a new design today for long-term production requires specific and detailed strategies. Preventing a production disruption due to a shortfall of components or long lead times is as easy as planning BOMs during the early stages of development.
Five-Step Check for BOM Completeness
|Have MPNs been checked?
Have associated land patterns been verified?
|Are parts up-to-date? Are any components obsolete or end-of-life (EOL)?||Are all components in the design accounted for? This includes mechanical parts like fasteners.||Is the spreadsheet clear and easy to read? Are there superfluous columns to remove?||Are land pattern file names saved in the BOM for importing and netlisting the design?|
Supply Chain Problems to Avoid
While in recovery, the semiconductor industry is still amid severe challenges brought about by manufacturing shutdowns and understaffing during the international COVID-19 response. Because of this, chip foundries have been unable to keep up with new demands, and inventories at some OEMs have dropped from a forty-day supply of stock on hand to less than five. Even standard discrete passives are experiencing lead times close to or over a year. This shortage has created a problem for some essential parts forcing designers to find alternative answers in components and circuitry.
Lack of Inventory
Global shipping problems have also disrupted the electronics supply chain. Some vendors cannot supply their customers due to the inaccessibility of their standard shipping channels. While shipping port congestion has decreased since the crisis of 2021, notable queues remain that endanger production schedules. Many designers have found that the typical parts they’ve relied on in prior designs are no longer available, and significant development resources are going toward sourcing replacement parts.
Over the past few years, another problem that has increased is the number of counterfeit parts flooding the market. Counterfeiters sometimes substitute false part numbers to repurpose general parts as higher-cost precision components. In other cases, old and outdated parts get sold as new items, and as always, there is a host of pseudo parts on the market. OEMs must learn to recognize and verify counterfeit parts while avoiding the questionable dealers selling them.
Best Practices for Planning BOMs
Check Part Prices, Availability Before Commitment
Assess whether parts used in the BOM are the best blend of circuit requirements and market considerations is the best bet. Designers can fall into the “same old parts” trap due to accustomation: since a part worked in a prior design, push it forward to the next. However, manufacturing changes may delay these components, increase costs, or render them unavailable. Always confirm the status of parts before committing to a long-term production plan for a new design or revision. It is also essential to verify component suppliers to guard against counterfeit components.
If parts are unavailable, there are multiple avenues to rectify a design:
- Alternative parts – Search for components or combinations that provide equivalent functionality. While costs may increase, replacements can keep a production schedule on track.
- Redesigned circuitry: In some cases, redesigning the circuitry may eliminate the need to use an unavailable part.
- Component redundancy: When using a part in a design with questionable availability, consider ways to create alternative solutions within the circuitry. For instance, designing the land pattern for the primary component and its alternative to the board would support either part at the location. While there may be more elegant solutions, and space constraints can preclude implementation, foolproof methods like this create multiple outs for procurement.
Plan Early, Revise Often
Don’t wait until the end of the design cycle to research the parts; tentative procurement should be in place as soon as the first pass at the schematic finishes. Otherwise, parts with long lead times may be unavailable for the scheduled manufacturing timeline.
Procurement can be challenging to balance, given that PCB design is highly iterative. However, electronic component specialists can assist with this task, ensuring component availability without compromising design intent.
PCBA Planning? Your CM Has Over 40 Years of Experience
A contract manufacturer is an excellent resource for help with planning BOMs and building circuit boards. At VSE, we have a dedicated engineering and procurement team whose focus is ensuring that components in your design provide the expected results. Starting with a review of the BOM, our component engineers will verify that all specified parts will function as expected and are readily available. Simultaneously, our procurement specialists will source these parts to find the best prices and lead times.
Our DFM involvement doesn’t stop there, though: our design engineers will review designs for potential problems that can bog down the manufacturing process and report back with their recommendations. For customers working on long-term builds, our departments will continue to monitor the availability of the project’s components. When the manufacturers of those parts depreciate product lifecycles, our team will be ready to update their recommended changes and keep your production rolling smoothly.