Safe to use an "NC" pin on CD4049UB as a tie point?

[dxm1]

I'm _this_ close to finishing my PCB layout for the Insanity Box, and I have an orphaned signal pin on the 4049. I need to get a trace from pin 3 out to the right side of the chip. Using .010 traces and routing between pins would push my neandertal etching technique to the limit.

Normally, I leave pins marked NC unattached. However, routing through pin 13 would put me right where I need to be. Both of my CMOS databooks label pins 13 and 16 as "NC", and both say pin 16 is not connected internally. Neither say anything definite about pin 13. Has anyone ever tried routing a signal through pin 13 on a 4049 (TI CD4049UBE)?

Thanks.

[slacker]

This datasheet http://www.alldatasheet.com/datasheet-pdf/pdf/11956/ONSEMI/MC14049B.html

says
"Note that pins 13 and 16 are not connected internally on these devices; consequently connections to these terminals will not affect circuit operation"

so I guess it would be alright to route traces through those pins.

[choklitlove]

if nothing else, you could go ahead and put a trace there, then clip off that leg of the IC.

[dxm1]

This datasheet http://www.alldatasheet.com/datasheet-pdf/pdf/11956/ONSEMI/MC14049B.html

says
"Note that pins 13 and 16 are not connected internally on these devices; consequently connections to these terminals will not affect circuit operation"

so I guess it would be alright to route traces through those pins.

That's the first manufacturer I've seen that mentions pin 13. All that I've seen (including TI) say pin 16 is not internally connected, but no mention of 13.

Thanks.

[dxm1]

if nothing else, you could go ahead and put a trace there, then clip off that leg of the IC.

Now that's an idea that I should have thought of. I don't know how many ECOs I've spec'ed that require lifting an IC pin out of the socket and soldering a wire to it... Good one, thanks!

[R.G.]

That's the first manufacturer I've seen that mentions pin 13. All that I've seen (including TI) say pin 16 is not internally connected, but no mention of 13.

Which brings up a couple of interesting points.

Different manufacturers do different things on "NC" pins. Some truly have the pin not connected inside the chip, so you can do as you like with it including soldering to it or cutting it off.  Some of them will REQUIRE that it be not connected to anything because they have put some manufacturing function on that pin and you get truly strange things if it's connected to anything. NC may mean " we didn't connect anything to this pin, it doesn't matter" or "you MUST NOT connect anything to this pin". And different manufacturers may make the same logic function and package with the same NC pin, but having those two opposite meanings. So you have to check the datasheet from the manufacturer that made your particular chip.

I have seen at least one engineer spend an entire week looking for a logic bug when the problem was a signal connected to an "NC" pin.

That being said, the 4049 is not likely to have such hidden traps.

[markm]

if nothing else, you could go ahead and put a trace there, then clip off that leg of the IC.

Very clever indeed.
I like it