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'[EE]: PCB routing across unused pin?'
2003\06\30@113546 by Alex Kilpatrick

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(I always hate putting EE on my subject line.  I have an undergrad
degree in EE, so I always feel like I should know this)  :-)
 I was wondering if there is any way to route across an unused pin pad on
an SMT PIC?  If I set up the pin as an output, then it is
high-impedence, correct?  So, to the circuit it is not there?
Thanks!
Alex

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2003\06\30@114127 by Herbert Graf

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> I was wondering if there is any way to route across an unused pin pad on
> an SMT PIC?  If I set up the pin as an output, then it is
> high-impedence, correct?  So, to the circuit it is not there?

       You must set it as an input, not output, and even then the voltage on that
pin must not go outside the allowed input for a PIC pin. What about bending
that pin up so it doesn't make contact with the pad? Are you doing SMD or
through hole? You could just cut the pin off. TTYL

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2003\06\30@131805 by Mike Harrison

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On Mon, 30 Jun 2003 11:39:46 -0400, you wrote:

>> I was wondering if there is any way to route across an unused pin pad on
>> an SMT PIC?  If I set up the pin as an output, then it is
>> high-impedence, correct?  So, to the circuit it is not there?
>
>        You must set it as an input, not output, and even then the voltage on that
>pin must not go outside the allowed input for a PIC pin. What about bending
>that pin up so it doesn't make contact with the pad? Are you doing SMD or
>through hole? You could just cut the pin off. TTYL

This would be a VERY bad idea for a 'production' product, as it would cause problems when (not if)
someone forgets to cut/lift the pin.

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2003\06\30@140020 by Herbert Graf

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> >> I was wondering if there is any way to route across an unused
> pin pad on
> >> an SMT PIC?  If I set up the pin as an output, then it is
> >> high-impedence, correct?  So, to the circuit it is not there?
> >
> >        You must set it as an input, not output, and even then
> the voltage on that
> >pin must not go outside the allowed input for a PIC pin. What
> about bending
> >that pin up so it doesn't make contact with the pad? Are you doing SMD or
> >through hole? You could just cut the pin off. TTYL
>
> This would be a VERY bad idea for a 'production' product, as it
> would cause problems when (not if)
> someone forgets to cut/lift the pin.

       I don't see why, the pin will already be set as input, so unless you are
doing something wierd with that trace the "cutting of the pin" is only a
backup.

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2003\06\30@165343 by Doug Hewett

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Except for very good reaason(s), such as a safety or security-based mandate from a customer, e.g., DOD, FAA, FDA, NRC, etc., why would any designer deliberately make a pin unavailable?

IMHO it is preferable to keep one's options open.  Why burn bridges?

Doug Hewett
Software engineer,
CSDP




{Original Message removed}

2003\06\30@172748 by Mike Singer

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Herbert Graf wrote:
> > > ...You could just cut the pin off. TTYL

  I am not sure mechanical (and power dissipation)
specs would be valid in this case.

Mike.

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'[EE]: PCB routing across unused pin?'
2003\07\01@014313 by Picdude
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I'll assume you won't/can't route between pins, but how about switching the functionality of the wire you need to come from the unused pins.  Yes, I know you code may not be as clean, but in most cases it should be just as functional, and code is cheap.  I've tweaked many a piece of code to help PCB layout.

Cheers,
-Neil.

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