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Subject:
From:
Kenneth Wood <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Kenneth Wood <[log in to unmask]>
Date:
Thu, 30 Jul 2009 07:44:52 -0400
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I would not use cross hatching in modern high-speed or RF designs, cross hatching is ok for designs that have no high-speed though.
We are to the point of taking the tightness of the prepreg weave into consideration
for impedance issues so a cross hatched reference plane is defiantly out of the question today.
To your question, the only issue I have ever seen, and continue to see, is warpage of unbalanced layers.
Use outer layer thieving pads and balance inner layers to avoid this and you will be ok.
Even the outer layer thieving is optional but I do it as often as I can. (some customers hate seeing it)
It's not very scientific, if you have a 6 layer PCB and layer 2 is a solid plane then make sure that layer 5 (at least) closely resembles.
Ken 
_____________________________________
Kenneth J. Wood
Saturn PCB Design, Inc.             
[log in to unmask]
www.saturnpcb.com


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: Thursday, July 30, 2009 4:03 AM
To: [log in to unmask]
Subject: Re: [TN] Hashing-Out Hatching

In my former lives, last century, I always cross-hatched, especially on 
inner layers. Never any problem with imbalance, better adhesion of 
solder mask, less risk of delamination etc. I still applied thermal 
breaks etc. The CAD package I used gave free choice of width/space 
dimensions. Testing of characteristic impedance over cross hatching 
revealed absolutely no difference or reflections (thickness of 
dielectric in our case ~0.3 mm), provided the space between the hatches 
was less than the dielectric thickness.

Another point I found is that a client had massive solid planes with 105 
µm copper on inner layers for a power application (hairy at best!!!). 
During pressing, he tended to have resin starvation, as it flowed to 
fill where there was no plane. He changed to a low-flow resin and didn't 
have enough in the non-plane areas. I advised cross-hatching with 5 mm 
width/space: no further problem and he still had enough copper to pass 
the curremt.

IMHO, it has everything going for it and nothing against it.

Brian

James Head wrote:
> I'll use hatched planes occasionally, to "even" etching across the board
> material, but only on mixed plane/signal layers.  It depends upon the
> board, how much copper tracking  and plane area is on the board and in
> what areas.
> 
> James
> 
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