Jack,

Brian's reasoning is the closest. Blistering, warpage, etc. are all 
considerations. A fabricator still must qualify his ability to build 
large unbroken copper areas for his UL certification. If they normally 
deal with large copper areas in their products, they will submit an 
appropriate test vehicle to UL for approval. A little side note, if you 
are building products that must have UL certification, then you must 
validate that your suppliers have certified to your type of construction 
(an entirely new discussion).

This all said, let's do a quick reality check with today's technologies. 
  Blistering problems, etc. are still a risk. But seriously look at 
today's boards. Circuit density is much higher using vias (holes) all 
over the place, which in turn break up large copper areas, naturally. 
Years ago component density was much less and designers took pride in 
designing boards with no vias, resulting in many areas of unbroken 
copper. Sometimes I think that today's CAD systems vie for who can place 
the most vias on a board.

So, I believe today's high design designs naturally break up larger 
conductive areas, resulting in a general loss of the fundamental 
reasoning behind the still valid recommendation. As RF and microwave 
designs increase in demand, so does the necessity for fabricators to 
re-qualify with UL, something that is normally done outside of the 
designers watchful eye.

On a side note, I see many instances where the reasoning for fundamental 
recommendations have been lost over time.

Gary

Jack Olson wrote:
> 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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