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I do not know if this is on topic, but which are the recommended footprints dimensions (or a reference document) for the SOIC_N and MSOP_N Packages?

In analog.com I can find only the outlines, and in the Ultra Librarian app, suggested by Analog Devices, the program do not show me which is the package, so I am not sure what I am having. I was unable to run the .PrjSrc scripts in Altium 16 either.

Normally I ended looking at some Google Images for a standard manufacturer, but never the same manufacturer, always an approximate guess for every package, not a specific procedure with the proper dimensions.

Click to Enlarge

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    \$\begingroup\$ Have you looked for the parts on SnapEDA? They publish both unverified and verified footprints. Altium is supported. \$\endgroup\$
    – filo
    Sep 28, 2019 at 12:05

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JEDEC publish dimensions for standard packages. Here is a list of dimensions for the narrow SOIC.

Individual component suppliers' published dimensions may differ from those slightly, depending on how they've implemented the tolerances.

However, the purpose of a board footprint, the solder pads, is to enable board assembly, so they will be slightly larger.

A large board manufacturer will usually optimise their footprints for their assembly process, which means tweaking the pads for their solder type (leaded or lead-free), solder volume (size of solder stencil aperture), heating rates, inspection methods, to get the best first time yield.

The component supplier's footprint, if they recommend one, is always a compromise between several assembly processes, so it's no surprise that different suppliers end up with different suggested pad layouts.

In general, the soldermask opening should be 'a bit' larger than the footprint of the package lead. This is to allow a visible solder fillet at the end and to the sides of the lead. This serves the purposes of making it possible to visually inspect the joint to check it's solder filled, to make it possible for surface tension forces in the molten solder to pull the package into alignment, and for increased area and solder volume to make a stronger joint. Make the pad too much wider, and you risk solder bridging between pads.

The ideal extra width for pads (side fillet) will vary with lead pitch, and between machine and hand soldering. There is more lattitude on the extra pad length (toe fillet). It's useful to have them quite long to allow you a large place to land your soldering iron tip, and the only penalty for excess length is packing density, until you get into high RF where parasitics become important. You would usually also provide a heel fillet under the package. It can't be inspected, but provides extra solder volume and strength to the joint.

I tend to use a footprint with minimal side fillets, and generous heel and toe fillets, as I hand solder, and am frankly not very good at it, so need all the protection I can get from solder bridging.

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  • \$\begingroup\$ Yes but... where should I take the footprints base dimensions from? \$\endgroup\$
    – Brethlosze
    Sep 28, 2019 at 5:53
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    \$\begingroup\$ @Brethlosze added the links to JEDEC, made clear the difference between standardised overall package size, actual package, and recommended footprint \$\endgroup\$
    – Neil_UK
    Sep 28, 2019 at 8:22
  • \$\begingroup\$ Thanks. I am looking for recommended footprints. I see from the link the pin sizes, but i do not know how to deduce footprints from them. \$\endgroup\$
    – Brethlosze
    Sep 28, 2019 at 22:06
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    \$\begingroup\$ @Brethlosze It's really, really, simple. There aren't any recommended footprints, but google around and you'll find plenty of examples. Take the pin sizes, and make them slightly bigger, without making them so big that they're so close they're easy to solder bridge. When you've done that, you'll find that what you've got is more or less what any of the 'manufacturer's recommended' ones are, different though they all may be in detail. Solder is a wonderful material, it takes up the detail difference between pad and pin. \$\endgroup\$
    – Neil_UK
    Sep 29, 2019 at 5:42
  • \$\begingroup\$ Great. That is the advice i was missing... \$\endgroup\$
    – Brethlosze
    Oct 1, 2019 at 3:29

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