How worried should I be if I route wider than 10 mil trace to 0805 pad?
Would 16, 20 or 24 mil trace cause soldering problems without making 10 mil neck?
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\$\begingroup\$ article on somewhat related subject in PCB Design & Assembly magazine. \$\endgroup\$– Nick AlexeevDec 1, 2012 at 21:30
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\$\begingroup\$ The article seems to have moved, but the direct link gives a 404 (possibly due to access restriction) \$\endgroup\$– hlovdalJun 14, 2014 at 13:03
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Even a 24 mil trace is narrower than the narrow end of a 0805 package. It would probably be OK on its own.
Any competent routing software will create thermal gaps, usually just called "thermals" between the pad and a wide trace. For a 0805, this would probably be one thinner connection on all three sides of a pad not opposite the other pad.
Even without thermal gaps, something as large as a 0805 should be fine with most processes. The issue is that the solder on the other pad melts before the solder on the pad with the large trace coming off it. The higher surface tension of molten solder relative to solder paste can cause the part to lever up and stand vertically only on the pad with the molten solder. This is called tombstoning, and is a real issue for small packages like 0402 and sometimes 0603 if corner cases.
Another way to fix this is to run a equally wide track from the other pad. That way the solder on both pads should melt at about the same time.
Also consider whether you really need such a wide trace right at the part. Can this part really handle the high current? Even if so, is the tiny amount of series resistance added by the thermal gaps really significant?
answered Dec 1, 2012 at 13:01
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\$\begingroup\$ +1 for the tombstoning reference. This can just ruin your day :( \$\endgroup\$– carveoneJul 20, 2013 at 15:22