Jack C. Olson
10G Circuit Board Designer
(630) 754-2431
The statement you made below got me thinking about something.
(I'm NOT disagreeing with you, just thinking about it.)

I know all the books and guidelines recommend thermal relief
and how to calculate for it, but my question is:

"If the board is being reflowed, and preheated, and the oven
is so hot that everything reflows no matter how many planes
they are attached to, then who needs thermal relief?"

My answer is: "Well, it would be a benefit for rework."

So my second question is: "For products that are throwaway
(not repaired), can we ignore the whole thermal relief question?"

For an example, we have solder joints that are connected to
many ground planes with many 8mil spokes (which totally blows
the whole concept of thermal relief anyway), but the joints
coming out of the oven are perfect.

blowing smoke?

Jack (aka the "challenging the rule of thumb" guy)






             JaMi Smith
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             12/09/2004 09:26
             AM

                                                                   Subject
             Please respond to         Re: [DC] FW: Bypass caps under BGAs
                "(Designers            using via in pad
              Council Forum)"
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                JaMi Smith
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<snip>

The problem here however is that on the bottom side of the board we want to
use a
via in pad situation, which virtually dictates that the via be isolated
from the
plane by a "Thermal Relief" if we ever want to be able to solder the
capacitor in
place, which means that in at least some instances, where we are going to
have a
component pad on the bottom side of the board, we also need a "Thermal
Relief" in
the corresponding planes.

<snip>

JaMi Smith

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