Who’s Responsible for the Footprint?

I recently wrote a bit about CAD library parts for QFNs and a reader posed an interesting question in response to it:

Okay, that makes sense.. But why don’t manufacturers of the part put out their footprints and schematic symbols for their parts in some common format?

That is a very good question. When you purchase or download a CAD package, it will typically come equipped with an established library. Those libraries vary greatly in coverage and quality though, and, of course, only cover parts available at the time of release — and only a subset of the most popular, at that.

Who’s job is it to make workable library components and or new ones? Ultimately, it usually falls to someone in the organization doing the circuit design. Some people will pay a third party to make the parts. NXP has made the complete library for its chips for the PCB123 CAD package. Some independent companies make it their business to create and maintain libraries. But, really, who should be responsible?

A component manufacturer needs to document a new chip anyway, but they’d have to make a library part for a dozen or so CAD packages for each part variation, depending on how much coverage they want. CAD companies would need to create maybe a hundred thousand or a million library parts, depending on how much coverage they want, but the CAD package is useless without the library. The designer would need to create just the library components needed for the specific design, but that could easily double to design time. I guess that’s why we have what we have — a combination of the above.

Still, the big question is: why isn’t their a standard format for the libraries? That would make everyone’s life easier. So, CAD folks, why no standard?

Duane Benson


6 thoughts on “Who’s Responsible for the Footprint?

  1. The question is more – why would the manufacturers spend resources on something that does not generate income for them. Sure they might sell a few more parts, but they sell LOTS of parts without a library or a ‘standard format’. Also think of the liability – “Oh my board doesn’t work, and I used XX’s library. I demand that XX pay for my failed boards…”

    It simply just doesn’t make sense. Ask PCBMatrix.com – Tom Hausherr has asked this question for a decade (at least, right Tom?). PCBMatrix finally came out with a software tool that generated the footprints, and now schematic symbols, for you. Pretty neat too. If you want something, and don’t have the time to create it, find it on the internet. I can bet for anything you’d like to do, someone has done it already, or will show you how.

    Vendors make and sell parts… PERIOD.

  2. You got it right Mitch.

    Vendors(component manufacturers) know how to make parts and what they are concerned about is what happens inside the package. Their business/technology
    interests ends at the edge of the termination.

    Many times land patterns must be tailored for the specific assembly process capabilities or the product’s specification when a high yielding highly reliable product/process is desired. In addition all components that meet a generic industry specification may be manufactured with differing termination dimensions and tolerances.

    Given their choice, component manufacturers would probably prefer not to be ask to supply suggested land patterns. But when the customer asks………they fee obliged to say something in the name of customer satisfaction.

  3. Standardized library format? How about a standardized CAD database format? So we don’t have to mess around with all these CAD translators and import utilities (most of which lose or distort a rather poorly documented **something** in the translation) whenever we have to exchange design data between Engineering and Production. GenCAD was nice but nobody seemed to buy into it.

    Yeah, I know. I’m dreaming.

  4. It is simply NOT viable to for CAD SW tools companies to create a “standardized” format. Simple problem – loss of customers. Why would Mentor/Cadence/others create a format that would allow their users to migrate to another tool?

    But, if you’re on a tool, your software vendor probably has a migration tool in place to translate FROM another tool. I know, I’ve used both Mentor’s and Cadence’s tools to READ IN either of the other’s databases. It just doesn’t make sense for the company to support a tool that ports to another CAD tool.

    Proof? Mentor has both PADS and Expedition, as well as BoardStation. I can convert from PADS to Expedition, but I can’t go the other way. Why? Because PADS is the lesser costly tool. Why would torMentor want someone to port to their lesser costly tool? Doesn’t make business sense.

    Now, because we’re such a developed world, you can almost ALWAYS find a way (or someone to do it for you) to convert from one tool to another. 🙂

    GENCAD was a nice thought, but not many people would buy it, and IPC is not in a position to support it into the future, sorry.

  5. Duane,

    I’ve been following your interesting articles regarding footprint (land pattern) issues and I am glad to see that someone is pointing the problems out.

    I’m sure that everyone is familiar with IPC’s 3-Tier library standard IPC-7351. That’s a good place to start.

    Yes, I’ve been saying for the past 10 years that component manufacturers should own up to the responsibility of providing CAD/CAE libraries for their electronic devices. Especially because I’m seeing some very complex unique component packages lately and it’s becoming increasingly challenging to accurately calculate a correct optimized land pattern (footprint).

    However, there is a major obstacle with getting the component manufacturers involved in CAD library generation. A CAD library must contain symmetry. i.e.: Every part in the CAD library must be built using the same construction rules or there will be massive chaos in the PCB design process.

    So how are you going to get 2,500 component manufacturers worldwide to follow the same rules for land calculations, a single measurement system, drafting line widths and sizes, ref des sizes, polarity marking, orientations (rotation), origins, land pattern and padstack names, layer assignments and support multiple CAD tools?

    Example: can you imagine a PCB layout that uses CAD libraries provided from multiple component manufacturers and they all use a different silkscreen line widths and ref des heights. Your design would look more like a circus than a layout.

    So even though I have been saying for the past 10 years that component manufacturers should provide their own CAD library I come to the realization that it’s much more challenging than everyone thinks. Also, like Mitch mentions, the liability of making a mistake is huge and could damage reputation as well as financial obligations.

  6. Mitch and Tom make some interesting points. But it is indeed in the best interests of the component manufacturers to distribute their parts in a library. Just as it is in their best interests to supply a datasheet in PDF format – ease of access.

    Semiconductor companies could influence the speed of adoption of a new part by publishing parts definitions, footprints and even simulation models at (or even BEFORE) the part’s release date. Interested engineers could then be evaluating the part from the library model, speeding the lag time between part NPI and its incorporation into finished designs.

    This increased adoption rate easily pays for the small amount of incremental effort on the part of the semiconductor manufacturers to provide a part definition.

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