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 > > --------------------------------------------------- > Technet Mail List provided as a service by IPC using LISTSERV 15.0 > To unsubscribe, send a message to [log in to unmask] with following text in > the BODY (NOT the subject field): SIGNOFF Technet > To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) > To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest > Search the archives of previous posts at: http://listserv.ipc.org/archives > Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 > ----------------------------------------------------- > --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------