This is another Book Gang, so Trash it if dis-interested !! Ed Current, Jack has replied quite effectively as have the other reply-eez on this copper thickness issue (Go Team!). The only statement I would like to assist Jack on here is the etching problems.... The problem with any 'thick' Copper is the edge definition of the trace, but as long as you have loose finished trace width requirements when fabbing (say....+/-.006") this will allow the fab shop some breathing room as far as undercut goes. ________________________ / \ / \ | trace | / \ -----/------------------------\------ under-cut ! The other statement that Jack made was that shops add dots to allow for even etching.....I think that he was referring to "Plating Robbers". What these Dudes do is to even up the plating process....not the etching process. Etching is fairly even no matter what densities of copper you have across the board. -BBBUUUUTTTT ...... What is definately a problem is one side of your board being all Plane, and the other being (wordt case..) 1 - 8 mil trace running for 1" in length. The Plating current draw in the tank increases as copper propegates to the heavier copper area, while that li'l ole 8 mil trace gets fried completely off the board with about 15 oz. of copper strapped to his back (instant Ice Scraper as we used to refer to these PCB's in the shop !! - the cold climate guys should be nodding to this one!) This is why they add dots around the open areas... It takes some of the 'heat' of the small guys during plating...Then naturally when etching, staff will measure all etching levels based on the small trace, not plane areas. Where this applies to you is in the plating dept... You will want to use more 'BASE' material, and less Plated material. Typical 'high' current apps might require 2.5-3 ounces Finished Cu Thickness, but you can rest assured that the Plating Line Guy will prefer to plate only .5-.75 oz. of copper on top of the balance in Base Copper Material. This reduces line time, as well as build up for via holes. Material Issue... Not many shops even carry 2 oz. material, so if your planning an exotic, allow a very long lead-time. (My FR-4 data sheets only go up to 2 oz. base Copper) Sorry for the book everyone! Les. (X-Fab-Meister turned CAD-Meister) [log in to unmask] =========================================== " He who doesn't have a good E-Mail Program, constantly re-types silly Quotes like this one !" -Les ===========================================