On Q2, you're looking at total trace width and fusing current. But the
thing about thermals is that because the spoke is next to a huge copper
area (presumption), the current can be much higher in the spoke than a long
trace of the same width without any risk of burning.
Doug Brooks has done some thorough investigations into this. He's got some
incredible resources: http://ultracad.com/article_temperature.htm
On Wed, Mar 16, 2016 at 12:35 PM, Guy Ramsey <[log in to unmask]> wrote:
> The standard requires the solder be wetted to the lead and the PTH.
> On Mar 16, 2016 3:30 PM, "Jack Olson" <[log in to unmask]> wrote:
>
> > I posted this to IPC TechNet, but I think many people are busy at APEX
> this
> > week:
> >
> > -=-=-=-
> >
> > Maybe I should know better than to ask two questions in the same email,
> but
> > they're related...
> > I got into a discussion about the hole fill requirement for some large
> > through-hole power devices and connectors. The supplier is worried about
> > using a "percentage" hole fill measurement, because he says that even if
> > the hole is 75% full (or whatever percentage we want to use) the hole
> wall
> > will not be WETTED 75%. He maintains that the cold solder can extend up
> > farther than the actual portion that makes a good joint. So he is looking
> > at the TOP PAD WETTING for verification of a good solder joint, even
> though
> > we don't require it.
> >
> > Q1) It seems like an inspection procedure looking for WETTING instead of
> > HOLE FILL is not what is intended in IPC, but does he have a point? The
> > hole fill problem is with Selective Soldering, not Reflow
> >
> > Q2) Wanting to provide bare board designs using good DFM practices, I
> would
> > be willing to reduce my thermal spoke widths so the solder will flow
> > better, but I can't find a calculation that would tell me what I need for
> > something like 10A. There is nothing about this in the IPC-2152 Current
> > Carrying standard. Is there a rough guideline I can use for current
> through
> > planes using thermal relief??
> >
> > thanks,
> > Jack
> >
> >
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