Estimated reading time: 6 minutes

Elementary, Mr. Watson: The Five Pillars of your Library, Part 4—Review

I trust that you have been enjoying this series on the five pillars of your library. Now that we have a single library managed using our revisioning, and we have lifecycle schemes organized so that we can easily find something in the component category, family, and subfamilies, we are now ready to look at one of our library's most vital principles and pillars: reviewable.

 I recently spoke with a company regarding its library and mentioned the availability of third-party component sources. I specifically mentioned Octopart, but there are now seemingly countless sites that provide excellent components to load up your library. His response was classic and pretty standard, "We don't use them because we don't trust them." I immediately responded, "Good, and you shouldn't." He was a bit taken back by that, but it's true; no matter the resource you use to load up your library, whether it's a third party or something you built from scratch, you should never blindly trust the information. Introducing assumptions into your design process is a recipe for disaster and using your fabrication and assembly process as verification of your components becomes very expensive. If you must, assume that every component is wrong and prove they are correct.

I believe in every company having at least two standards of operation (SOP) as the very foundation of their component library. The first document is the component creation process, and the second is the component QC process.

In an industry that demands perfection, you can’t just believe your library is good enough; instead, you must know. But what does it mean to be good enough? We got the board through fab and assembly, and maybe it went through some compliance checks. Does that necessarily mean it was correct? No, it could be that you just got lucky.

Off the coast of a somewhat rugged area of North Carolina, there stand three lighthouses. Being such a harsh area for naval vessels, it is a well-known area for shipwrecks. Contrary to belief, though, a ship captain will not go from lighthouse to lighthouse when he is coming into port. Instead, he lines up all three lighthouses where he only sees a single light. Much in the same way, during the component auditing process or review, we verify that all the lighthouses are lined up, and we should only see a single light.

Component Verification Standard
For any verification process to be successful, it is established on a known standard. What do I mean by standard? It is the known benchmark to line the data.

The Datasheet

The first verification document for all components is the datasheet. It is usually the very first document that engineers and librarians go after. If the process does not start there, we will be setting ourselves up for major problems down the road.

But, (and that is a big but), some datasheets have been known to be wrong. This is often because a single datasheet is trusted way too much (assume it is correct), the problems with those datasheets usually end up on PCB designs, and you don't find out until you get into assembly. Then, before you know it, you are making that long walk to the manager's office.

When this happens, and it will at some point in your career, document it. If you find such a problem, it could become a habit for that vendor. No company can afford to fact-check datasheets and components by running PCB board runs. You should consider dropping them from your preferred vendors' list, or at least red-flag them. You caught a problem that may exist in other parts they provide.

Another strategy is that you should always have multiple suppliers for any components in a design. That provides a couple of things in our process. First, it gives us an alternate part if our first choice falls through for some reason. The other advantage is that it provides another datasheet to compare the component.

When multiple manufacturers are available, it is best to pull every datasheet and compare them to determine whether anything is out of line—lining up those lighthouses, then comparing and deciding what we see.

IPC Standards

Fortunately, we are not left to our own devices to determine whether a component or a datasheet is correct. There are several standards provided by the IPC, which has been the leading authority in the printed circuit board industry since it was established in 1957. I have never read a standard provided by IPC that I did not like. The criteria that would help in the review process are those in the Design and Land Pattern category: IPC-2221, IPC-2222, IPC-2223, IPC-7351C (surface mount components), and IPC-7251 (through-hole components).

I would highly recommend starting with the IPC standards as the foundation for setting up your component model libraries.

IPC-7351 and IPC-7251 give a very detailed breakdown of the component category. You are then giving the specific naming convention which is tremendously helpful in the architecture of your library.

Through standards developing organizations (SDOs), the standards are reviewed regularly and updated to line up with changes in the industry. Although this falls a bit under the fifth pillar of “tailored” (but is an excellent place to put it), keep up with the revised editions of the standards to determine whether those changes affect any of the models in your library, for example, with the release of IPC-7351C from the previous version. A move was implemented that changed the shape of any rectangular pad to round off the corners. These changes were implemented because the sharp turns act as antennas and help in the routing with a 45-degree angle trace.

‘New’ Components Quarantine
If you don't already, establish the guideline that no PCB will be released and fabricated with any components in a “new” state. What can be done is to have a separate folder which quarantines all new components. Those components should not be trusted or used in released designs until the audit is finished.

Make it a rule that you cannot use any component in a design that has not gone through an audit process. Follow the “golden rule” of review: The person who did the work cannot review it. What’s important is getting another set of eyes looking at the component. It just so happens that the person who did the work does not have an objective view but rather a subjective one. It’s probably best to have a few people to act as the review board.

Component Circle of Trust
The component verification process is never-ending. Some look at it as having a finish line. But actually, there is no endpoint to improvements that you can make to your library. In other words, it's not a straight line but rather a circle with no beginning or end. With that said, there are several other component verification resources you can use to improve the library. Fabrication, assembly reports, third-party DFM software, and even field service reports are beneficial to determine if the failures resulted from a component level issue on the PCB. If so, make improvements in your library. Keep your library of the highest quality possible. You won't regret it.

John Watson, CID, is a customer success manager at Altium. 

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