Gary,
While the book may refer to possible heat thieving, in practical
application it has no effect. Pick up any number of commercial PCBs and
you can easily see that this IPC standard is not used. As an engineer
that happens to do PCB layout, I want my traces to be as robust as
possible. I typically use 10 mil traces which happen to be about as wide
as a given pad in my application. When necking down unnecessarily you
can produce manufacturing problems near the pad. If heat thieving is a
problem, I'd bet we have a process problem. The key word in the IPC spec
is the "possibility" of heat thieving. IPC specs are published as a
guide, not a law. Mo' metal, mo' better.
Cheers,
Ron Scott C.I.D.
Sr. PCB Designer
Texas Instruments
Storage Products Group
Tel: 214.567.4715
Cell: 972.816.7978
Fax: 972.761.5070
[log in to unmask]
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Gary
M. Koven
Sent: Wednesday, July 27, 2005 14:06
To: [log in to unmask]
Subject: Re: [DC] Trace width ratio to pad
Allen,
Chapter and verse would be IPC-2221, Sec 10.2.2 "Lands for Surface
Mounting", from which I quote the salient sentence:
"The possibility of heat thieving is reduced by "necking down" the
conductor near the soldering area."
That oughta do it.
Best Regards,
----------------------------
Gary M. Koven, C.I.D.
Engineering Services Manager
Dynazign, Inc.
806 Tyvola Road, Suite 100
Charlotte, NC 28217
P: 704.405.1234 x210
F: 704.405.1402
http://www.dynazign.com/
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Allen T.
Maddox
Sent: Wednesday, July 27, 2005 2:47 PM
To: [log in to unmask]
Subject: [DC] Trace width ratio to pad
Hey Folks,
I was always told to NOT exit a pad, especially a SMT pad, with a trace
the same width of the pad for the reason of dissipating the heat off the
pad and creating soldering issues.
I have an engineer who doesn't believe me and wants proof. Does anyone
have any articles that support what I've been taught, or have I been
mislead all these years?
Thanks,
Allen Maddox C.I.D.
Sr. PC Board Designer
GAI-Tronics, Corp
610-796-5854
PO Box 1060
Reading, PA 19607-1060
[log in to unmask]
www.gai-tronics.com
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