No, you won't find it documented anywhere, "Thou Shalt Not" run a trace
under a 1005. BUT.. You should not need a standard to justify "good and
acceptable design practice"
How about this:
To route a trace under a 1005 resistor or cap falls in a category called
"Design to Fail".
1) there is scarcely enough clearance to run even a really small trace
under a 1005. If your land patterns are built to IPC-7351, you've only
got about 0.25 mm or less between the lands. There is no room for a
reasonable clearance.
2) IF you could fit the trace, it's likely that the solder mask oversize
around the lands will expose the trace resulting in a very high
probability of solder bridging in a location that is hidden from view.
3) Consider the profile... Land area = base Cu + additive Cu + finish.
Trace = base Cu + additive Cu + Solder Mask. The solder mask coating is
MUCH thicker than the surface finish on the land area. This sets up a
HIGH spot between the lands, an excellent fulcrum on which the part can
teeter. This dramatically increases the likelihood of tomb stoning.
So, bottom line is; If it is your heart's desire for the board to be a
top candidate for failure, go ahead - run a trace under your 1005's.
On the other hand, if you want the circuit to actually work... Do not
run traces under your 1005's.
Denis Lefebvre, CID+
Sr. PCB Designer
Finisar Corporation
(408)542-3832
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Tempea, Ioan
Sent: Friday, February 16, 2007 5:40 AM
To: [log in to unmask]
Subject: Re: [DC] Traces between 0402 pads
> Dear colleagues,
>
> is there any standard saying that traces should not be routed between
0402 pads, i.e. under the component? I have a serious discussion and
really need to back it up with a formal document.
>
> Thanks,
>
> Ioan
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