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I've often heard a couple of "good practices" for TQFP/QFN ICs fanout:

  • Do not route corner pins at 90°, instead the track must come straight to the pin: enter image description here

  • Do not short the signals directly at the pad, but rather extend the track and do the junction outside of the footprint:

enter image description here

I imagine it doesn't really make a difference from a signal integrity perspective, but rather help/simplify AOI. Is there an official IPC/JEDEC guideline for those, or are they just "good practices"?

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  • \$\begingroup\$ never heard of your first recommendation. Nor actually about the second, which makes preciously little sense in any sensible SMD process I could think of. \$\endgroup\$
    – Marcus Müller
    Commented Dec 13, 2021 at 15:40
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    \$\begingroup\$ Often, your pads will likely be drawn as "Not Solder Mask Defined", which means that the solder mask pulls away from the pads, and the copper shapes define the reflow geometry. Routing the corners differently (image #1), using wider traces under the pads (image #1), and shorting pads directly (image #2) all change the shape of the pad. Additionally, example 2 has a higher chance of producing visible pad-pad shorts, which are electrically OK, but might cause issues with inspection standards or require you to double-check the design. I don't know relevant IPC/JEDEC to quote. \$\endgroup\$
    – W5VO
    Commented Dec 13, 2021 at 16:35
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    \$\begingroup\$ @MarcusMüller I've heard from my PCB assembler that their AOI does not like pins tied together like in the second question. The AOI has a hard time differentiating that from a solder bridge. Never heard that you should not go 90° out of a pad though. \$\endgroup\$
    – Klas-Kenny
    Commented Dec 13, 2021 at 17:37
  • \$\begingroup\$ @Klas-Kenny ah, that kind of makes sense. But then again, if you know these are meant to be bridged, it's possibly simply a matter of telling the software to ignore these. So, hm. \$\endgroup\$
    – Marcus Müller
    Commented Dec 13, 2021 at 17:39
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    \$\begingroup\$ @MarcusMüller Sure, but then you make some change to the PCB so they should no longer be bridged. And then the AOI is programmed to ignore those possible solder bridges. Better to avoid it in the first place, even if it's usually not a major issue. \$\endgroup\$
    – Klas-Kenny
    Commented Dec 13, 2021 at 18:25

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