The methoed of layering dry film can be used up to about 20 oz of plated copper, it is very accurate and fine featres, there is some concern to get the surface flat, and plating bars help. THe most accurate I have produced is 10 mil lines and spaces in 20 oz. I started with 1/2 oz and did not use a tin etch resist , only a fast etch to keep things acurate. You can buy copper up to 40 oz from many copper roof sheeting companies, use full soft 110 and clean them well before laminating or dry film lots of oil and crap . The best I got up to in etching only is about 12 -15 oz and the accuracy was not good, 30 to 50 mil lines. most companies that manufature heavy copper use a combination, start with 3 to 5 oz and plate up 3 to 5 oz, cheeper , less time in the copper tank and good acuuracy about 2-3 mils per oz line and spaces. The thicker copper in the vias makes the board very strong and will not crack even with high theremal cycling. If you need help my e-mail is [log in to unmask] --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 847-509-9700 ext.5315 -----------------------------------------------------