Hello,
Perhaps I can give some input to this.
The fact that the signal will run in a jumper does not make it very
different from a signal running in the PCB.
As it runs outside the PCB, it will be a microstripline configuration (taken
for granted that your design has some form of ground plane in it.).
This means that compared to a signal trace inside the PCB between 2 power
planes, the signal will run slightly faster in the jumper.
Compared to a trace on the outer side of the circuit board, the propagation
speed is almost identical.
If this is an advantage or a problem depends on the signal it self but an
educated guess is that the different in propagation delay caused by this
doesn't matter much.
On the other hand, running a long way with the jumper may be a problem. -The
same rules applies to a jumper as to a PCB trace when it comes to high speed
signals. If the trace becomes too long, it may require some form of
termination but again, no difference between normal PCB wires and jumpers.
If the net is not a high speed net, then the length doesn't really matter.
Important here is of course the edge rates of the signal in question. The
frequency means close to nothing.
For more info on the high speed and EMI issues, take a look at
http://www.dde-eda.com/highspeed.html ( it should be fairly non commercial)
Cross talk? Again, really no difference. Running in parallel (side by side
or on top of) with another signal can cause cross talk problems but as said,
no difference.-Make sure you place the jumper as wisely as you would place a
PCB trace.
EMI: Again, same rules as for a normal PCB trace. -If you run the jumper
unwisely, you can cause EMI. but that is also true for any PCB trace!
The most important factor is to minimize the so called loop area which is
the area covered by the loop formed by the signal trace and the return
current path. If you have a ground plane, your return path will be right
under the wire so unless you pass over a slot or gap in the ground plane
that causes the return path to deviate from the straight line, you should be
OK
Hope this helps
Per
_________________________________________________________
Per Viklund
Tech mgr.
Dansk Data Elektronik AS / DDe Sverige AB / DDE USA inc.
mailto:[log in to unmask]
http://www.dde-eda.com
_________________________________________________________
----- Original Message -----
From: "Carroll, George" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, August 23, 2000 9:02 PM
Subject: [TN] Jumpers
> Ladies and Gentlemen,
> After assembly of a board, it was discovered at test that there was an
error
> in the fab board causing a signal short. The inner layer short was cut
and
> a jumper installed to repair. I request guidance regarding the allowable
> length for a jumper. I believe the linear length of this one to be about
4
> inches. Can the installation of a jumper on a board's surface cause EMI
> problems?
>
> George Carroll
> SE&A
>
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