JoAnn Amerson wrote:
>
> Good morning all!
>
> I need some simple (ha, ha) answers to a question.
>
> We have a board with 1 oz copper.  One of the traces (external) from
> a connector to a shunt resistor needs to be rated to handle a 5 amp
> current.  It has a 20° rise above ambient.  This means it needs to be
> about 75 mils wide.  The pads on that resistor are finger-shaped
> (oval) - .070" X .124".  The trace is connected to the end of that
> pad.  Is there a problem with running a wide trace into a pad that's
> a bit narrower?  We are already limited on space so entering the
> pad along the side is not an option.  I'll bet some of you have some
> terrifically complicated formulae for figuring out how much current a
> pad of *x* size can handle.  Would anyone like to try to help us with
> this problem?  Any and all answers are appreciated.
>
> JoAnn L. Amerson
> Design Librarian
> Red Lion Controls, Inc.
> E-mail: [log in to unmask]
> Voice: (717) 767-6961 ext 6308
>

If it's a thru hole resistor I wouldn't worry much about a 5 mil
difference, especially since the calculator says you only need
.068" width to handle 5 amps at 20 deg rise.

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