Joerg, I would have to believe that it is the old problem of a little knowledge being misapplied by the uninitiated. A general comment on a rule or practice then being taken to further extremes and actually misapplied. Sometimes it may be software initiated, some packages actually have default rules that start out your design with thermals on 'all' plane connections. i.e. Protel P99SE (quite possibly the current AD software also), the default plane connection style rule on a new PCB is for "Board" (everything, vias and pads) to be thermally relieved. So the less knowledgable and experienced get introduced to the silly practice by their acceptance of software package defaults.
Certainly seems silly doesn't it? Then there is the problem of all the discontinuities caused in the planes by these unnecessary thermal reliefs. It is fairly common to see required thermal reliefs that are actually starved connections because of all the unecessary reliefs impeding a good connections to those required points.
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Sincerely,
Brad Velander.
"Joerg" wrote in message
news:n_xlj.1883$EZ3.344@nlpi070.nbdc.sbc.com...
> While checking a layout for a client I saw this for the umpteenth time:
> Trace connections to a plane via thermal relief, not in a solder area
> where it would thermally matter.
>
> Question: Was it taught once upon a time that thermals must be used
> everywhere? Or is there some other reason why it\'s done so often?
>
> --
> Regards, Joerg
>
> http://www.analogconsultants.com/