Hi Jack,
The problem with the IPC statement is that it ONLY takes into account the manufacturing reasons to hatch the planes, and does not take into account the electrical reasons NOT to hatch a plane.
At speeds somewhere before 1 MHz, signals begin to travel through the board as transmission lines which means (basically) that the signal travels on a signal layer and the return current travels on the nearest copper (usually a plane whether power, ground, or no connect). If the (return) plane is cut into a hatched area, then the return current is constantly crossing those little "splits" in the plane or manuvering around them and that can be very, very bad for signal integrity. In really slow speed designs, it does not matter..... that's why so many of us used that practice a long, long time ago, but with today's signal speeds... even the slow ones... going a lot faster than they used to in the old days, it may be a problem.
At what speed hatched planes will affect the signals on any given board is based on many things, but the bottom line is that it is probably best not to use a hatched plane as a return current layer (whether internal or external) on any board unless you are very sure of what you are doing. So the bottom line is (IMHO) that the IPC statement should have the caveat that the large areas of planes might be hatched IF it does not affect the electrical characteristics and signal integrity of the board.
Thanks,
Susy
---- Jack Olson <[log in to unmask]> wrote:
> Well, although most of our boards have enough features
> that break up planes, and we probably get enough good
> adhesion, there are designs I've done that have some large
> empty areas. Quite often I leave the copper in there.
> (why waste time and chemicals etching away perfectly
> good copper?)
>
> but I guess I should add another entry to my ever-lengthening
> CHECK LIST, to look for cases where hatching makes sense.
>
> Thanks everyone, for all the great responses.
>
> Jack
>
> .
> On Fri, Jul 31, 2009 at 7:47 AM, S. Roy <[log in to unmask]> wrote:
>
> > Good morning,
> >
> >
> >
> > We use unconnected, cross-hatched pours (or thieving) on external layer
> > crackers for balanced construction. Internal layers and external “power”
> > pours are solid copper and pinned with vias. Because some of our products
> > require very large boards, with very dense circuitry and components on only
> > one side of the board, we have some asymmetrical designs where warpage is
> > kept to a minimum from adding cross-hatched pours. Thanks…
> >
> >
> >
> > Respectfully,
> >
> >
> >
> > Steven D. Roy, CID
> >
> > PCB Designer
> >
> > Audio Authority Corp.
> >
> > 2048 Mercer Road
> >
> > Lexington, KY 40511-1071
> >
> > (859) 233-4599 X-159
> >
> > [log in to unmask]
> >
> >
> >
> > -----Original Message-----
> > *From:* DesignerCouncil [mailto:[log in to unmask]] *On Behalf Of *Karl
> > Bates
> > *Sent:* Wednesday, July 29, 2009 10:14 PM
> >
> > *To:* [log in to unmask]
> > *Subject:* Re: Hashing-Out Hatching
> >
> >
> >
> > Recently I had a board that had a lot of solid copper planes, and it would
> > take whatever shape you would bend it into.
> > When I did the next rev, I crosshatched the copper, and added pinning vias
> > within the hatching.
> > Now it is more dimensionally stable.
> > Keep on hatching boys and girls.
> >
> > Karl
> >
> >
> >
> >
> >
> > ------------------------------
> >
> > Date: Wed, 29 Jul 2009 19:57:30 -0400
> > From: [log in to unmask]
> > Subject: Re: [DC] Hashing-Out Hatching
> > To: [log in to unmask]
> >
> > This might be one of those archaic things from long, long ago ( in a land
> > faaaaaar away) but I recall using cross hatching and it seems it had to do
> > with either a solid plane acting as a heat sink at assembly, but again that
> > is an old memory. I also remember that the x hatching on flex was for
> > increased flexibility.
> >
> > Anybody got a clue?
> >
> > p.
> >
> >
> >
> > *From:* DesignerCouncil [mailto:[log in to unmask]] *On Behalf Of *Scott
> > Riley
> > *Sent:* Wednesday, July 29, 2009 7:51 PM
> > *To:* [log in to unmask]
> > *Subject:* Re: [DC] Hashing-Out Hatching
> >
> >
> >
> > The majority of my designs are flex circuits and I use cross hatching for
> > GND planes and large conductors all the time. This is done for flexibility.
> > However, I have never used it in on a PCB design.
> >
> >
> >
> > I’d be curious to know why it is recommended.
> >
> >
> >
> > *From:* DesignerCouncil [mailto:[log in to unmask]] *On Behalf Of *Jack
> > Olson
> > *Sent:* Wednesday, July 29, 2009 7:18 PM
> > *To:* [log in to unmask]
> > *Subject:* [DC] Hashing-Out Hatching
> >
> >
> >
> > Greetings,
> >
> >
> >
> > I was just reading through the latest draft of IPC-2222,
> >
> > and stumbled into the advice in section 10 regarding
> >
> > "large conductive areas", where we are advised to
> >
> > use some kind of etched pattern (cross-hatching)
> >
> > for any area larger than a 25mm diameter circle.
> >
> >
> >
> > I have done this exactly once in the last 22 years,
> >
> > does anyone else do this?
> >
> >
> >
> > Has anyone ever experienced a problem by NOT doing
> >
> > this? (not counting soldermask over HASL)
> >
> >
> >
> > Jack
> >
> >
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