One argument for using is 1/2 oz on internal layers is a reduction in line width variation. There are very few PWB suppliers that can supply supply a 4 mil line +/-20% on 1oz copper. In addition, mixed copper thicknesses on a layer pair [i.e. lyr 2 (top)and lyr 3 (bottom)] result in reduced yields. I also don't believe there is anyone who can honestly quote a 3 mil line +/-20% on 1oz copper and maintain the specification. nwbluez ---------- From: TechNet-request To: Technet Subject: Half ounce internals Date: Friday, February 16, 1996 4:40PM A strong consideration for not using 1/2 ounce copper on internal layers, is that you only half the width of copper to make a connection at the barrel of plating. Possible problems. Be careful. May not be reliable. Norm Einarson