Hi JoAnn,
 A lot factors have to be taken into account but in my humble opinion, everytime you neck a trace you raise the temperature of the necked section and in effect create a fuse condition. Keep the necks as short as possible and lay a duplicate trace or double the copper.
Ted Nathan
Sr PCB Designer
[log in to unmask]

---- DesignerCouncil(a)ipc.org's Message ----

Now that I have EVERYONE'S attention.........I have some questions about
necking down conductor widths.

My boss and I were talking yesterday about several isues that have arisen
lately.  One of them was a question one of our product engineers (senior tech)
had about necked down widths on conductors on one of his products.

If we have determined that we need a 15 mil wide trace (by using the conductor
width nomograph in the IPC spec), is it safe to neck it down to 10 mils for a
short distance?  If so, define short.  Or do we assume that 15 is the absolute
narrowest a trace can be for ANY distance?  If we can, how can we determine
what is a safe amount to neck something down for a short distance.

The way Cadstar handles conductors is to assign them a "track code" and
then that code is given a full width and a necked width dimension.  Some of the
necked widths (not set up by me) are as much as 50% smaller than the full
width.  Is there a "standard" of some sort that we should have been using?
Would anyone out ther like to tell me what they use?  I'm open for suggestions.

And as a little personal note - Frank Kimmey and Bob Vanech - where were
you two this morning?  I tried calling each of you at about 8:45 EST.  No
response.  My first line of defence was AWOL!  Hope this means you're sitting
by a pool somewhere with a long icy lemonade!

My thanks to everyone who can help me.

Jo

JoAnn L. Amerson
Design Librarian
Red Lion Controls, Inc.
E-mail: [log in to unmask]
Voice: (717) 767-6961 ext 6308

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