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Dealing With Supply Chain Woes? Try Using Variants

supply chain, pcb design variants

The PCB supply chain can be very volatile with inventory shortages rolling between various types of components. Most recently, shortages have been endemic in semiconductors, something which industry veterans have experienced repeatedly in the past. Dealing with these problems involves two important strategies: identifying alternatives, and preparing to use them in production designs.

Alternative components are usually easy to identify. They can be found from semiconductor product pages, data sheets, search engines, and application notes. Some components are pin and package compatible, so they can be drop-in replacements for out-of-stock components. Other components are comparable in terms of capabilities but are not perfect replacements. Based on available components, it may be desirable to build variants of a PCBA early and place these into production on an as-needed basis.

When to Create Design Variants

The concept in PCB design variants is simple: multiple versions of a design are created with slight variations. In the case where design teams have to deal with low inventories and need to find alternative components, PCB design variants can be created with alternative parts. This gives a team ready-made designs that can be quickly put into production as inventories and component sources change.

The trick to managing variants involves identifying the best components with which to create these variant designs. Not all components have replacements that require minor changes. For some parts, the package and capabilities are totally unique, and there are no replacements that can be used to create variants. So, an important part of variant management is narrowing down to the component groups to use in each variant.

Find the At-Risk Components

The most at-risk components will vary with each type of design and the overall state of the supply chain. With semiconductors being the most complex components in any PCBA, they are perpetually at risk to some degree. This is in contrast to something like passives, which can have many perfect substitutes even when supplies are low.

The table below outlines some risk profiles for common component groups. From this table, it would make sense that design variants be planned primarily around the most complex groups of components: processors and ASICs.

Highest risk: Processors (MCUs, etc.)

- Drop-in replacements only in the same part family

- Very few alternatives from other vendors

High risk: ASICs with special functions

- Many part replacements

- Not all replacements are compatible

- Some functions can be replaced by implementing in logic

Moderate risk: Power ICs and simple ICs

- Many part replacements

- Some are package-compatible

Low risk: Discrete semiconductors

- Many part replacements

- Many are package-compatible

- Many are pin-compatible

Lowest risk: Passives

- Plentiful replacements from many vendors

- Highly standardized packaging

The risk profiles from this table depend heavily on the presence of replacements. When few replacements are available, the risk profile is higher. The other major factor is the effort required to use a replacement; when implementing a replacement is more difficult, then the risk profile is also higher.

Set Priorities

The next step after identifying risk is to set priorities for inclusion in variants. You may be able to identify 10 suitable parts for your main system processor, but that does not mean you should create 10 variants around each part. Prioritize the most important parts for replacement by weighing a few different factors:

  • Cost/time to create each variant
  • Parts quantity available to support each variant
  • Cost differences in the final assembly
  • Capabilities differences between components

By prioritizing certain components for use in variants, you can limit the number of variants for a product that need to be managed.

How Many Variants Per Product?

There is no good answer to this question. Some companies take an agile approach and will develop a variant as soon as a need arises instead of pre-building multiple design variants. An important point to note is that the number of variants can increase very quickly as you try to support multiple part variants of the same component.

Suppose, for example, you have a required microcontroller with two alternative part numbers in unique packaging. The total number of possible variants for this design would be 3 variants. Now suppose you need to pair this with a power regulator that also has two alternative part numbers in unique packages: the total number of possible variants needed to hit this design target just increased to 9.

As the number of design variants increases, the agile approach begins to look more attractive. Designers and purchasing teams will have to carefully manage their available inventory, sources, and capabilities requirements to bring the variant count to a manageable level. Make sure you consider the risk-reward profile for a design and make sure you have a system in place to track data for your design variants.

Whenever you need to manage data on design variants, you can quickly make the component changes you need with the complete set of design features in OrCAD from Cadence. OrCAD includes the industry’s best PCB design and analysis software that integrates with a powerful data management platform. OrCAD users can also access a complete set of schematic capture features, mixed-signal simulations in PSpice, and powerful CAD features, and much more.

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