Re: [SI-LIST] : Of thermal reliefs and signal integrity......

Mark Nass (markn@rccorp.com)
Wed, 13 Oct 1999 15:18:52 +0100

Thermal Reliefs are not for improving heat dissipation, they are
for retarding it. They are used so that when you put a soldering iron
to the lead there is enough heat so as not to get a cold solder joint
and to be able to remove the part. Nowadays everybody uses solder pots or
reflow so thermal reliefs are not needed, and they also cause the problems
you mention. We use direct connects for everything, vias & thru holes.

Mark

At 02:39 PM 10/13/99 -0400, you wrote:
>I was hoping that somebody out there might have a report
>that can help me out. I know that I can find it but it also
>might be useful to others facing a similar problem. Under
>the guise of this is always that it has been done and we
>can't build boards otherwise (technical data conspicuously
>absent). I am being told that all power plane connections
>even SMT devices are connected to the plane via thermal
>reliefs (four spoke I suppose)
>
>Not only is this unnecessary in that the thermal drop of the
>escape etch of the SMT pad should be the same or better
>than four spokes, but inductance to the power plane is
>increased and the power plane is chopped up, especially
>in high density BGA areas where you need it the most.
>
>If you have a report that shows this, or think that I am off
>my rocker, please post as I imagine that many folks reading
>this may be in a similar situation.
>
>Thanks,
>
>Michael
>
>The bounds of Time, Space or Mechanics should never stand
>in the way of a perfectly good idea.......
>
>The time is gone, The email's over, thought I'd
>something more to say.........
>
>Michael C. Greim Consulting Engineer
>Mercury Computer Systems, Inc email: mgreim@mc.com
>199 Riverneck Road V: 978-256-0052/x1607
>Chelmsford, MA 01824-2820 F: 978-256-4778
>
>
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