Forum: PCB Design & Technology need to separate pads on logic board (is this possible?)

von EurekaTechSolutions (Guest)

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Need help/suggestions regarding logic board pads.

There are a few pads directly next to each other on a logic board that 
appear to be connected and should not be. My understanding is that 
leaving them this way will short out other areas of the logic board. I 
can see that the copper underneath is what permits this connection from 
one pad to the next when tinning the pads. Is there a way to separate 
these connections so they may be individual pads on the logic board (as 
they should be) rather than connected pads?

von Joe F. (easylife)

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A picture of the logic board area in question would be helpful to get a 
better understanding of the issue.
Is it an existing board, and you like to modify/rework it?
Or is it a PCB design, and you intend to change the design rules in 
order to improve manufacturability?

EurekaTechSolutions wrote:
> I
> can see that the copper underneath is what permits this connection from
> one pad to the next when tinning the pads.

Usually this is the job of a solder stop layer...

: Edited by User
von Eureka T. (Company: EurekaTechSolutions) (eurekatechsolutions)

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Here are pictures of the existing board where at the center, the pads 
should be separated by a black color. The 1st two pictures are the same 
(could not delete it). The 3rd picture is a similar problem that some 
pad is left, but difficult to keep them from connecting. What can I do?

: Edited by User
von Klaus (Guest)

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To me, it looks like these pads are connected by intent, not by 
incident, an irregularity or even by mistake.

You may be sure about that, being unwanted. In case you have any doubt, 
we could give hints, checking evidence.

However ...

In order to remove unwanted copper, you could cut it carefully, as 
this thin copper layer is an absolutely delicate thing. Usually it needs 
some experience to get this done the proper way. I would propose you, to 
try it with another board which may get rotten without loss.

The case, where solder unintentionally flows to a neighbor pad its most 
often caused by using to much solder. But this often occur even to 
experienced people. You may use desoldering braid. It is sold in a 
variety of diameters. For a good contact and material connection is 
sufficient to have solder beneath the pad and the circuits (or 
connectors) contact. No need to any solder "mountain" or even a "hill". 
Check whether the binding is sufficient by gently trying to lift the 
contact - BUT CAREFULLY.

Good luck. :-)

von Joe F. (easylife)

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The pad shown in IMG_3003 looks totally fine to me.
It looks like there is GND on the outer right pad plus the mounting pad 
(apparently it's the footprint of a FFC/FPC connector).
The two connected pads seem to carry some supply voltage, designers 
usually choose to use several FPC traces to reduce current load on each 
Both pads are connected by a common copper area outside the pad area, so 
no reason to worry, even if it looks like a short.

The situation in IMG_3004 might be similar, at least the two outer pads 
of this 3-pad group seem to be connected by a common copper area (above 
the pads).
I can't tell, if the pad in the middle also carries the same signal.
Solder and flux remains unfortunately avoid to see the copper traces.

Maybe you could clean this area with the help of some solder wick and 
PCB cleaning solvent, and shoot another picture of this area?

von Joe F. (easylife)

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If this is a connector to a display or something similar, it also could 
help to look into the datasheet to find out, which pins/traces carry the 
same signals.

von Robert P. (Company: SysPCB) (robertpeng)

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If the PCB is just for testing, you can use a knife to cut the unwanted 
copper,then the PADs won't connect with each other, this won't affect 
function of PCB. If the error is in batch PCBs, you have to re-order PCB 
from your supplier.

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