1oz vs 2oz copper - Page 1
Forum section: electronics / projects

author: fivefish
author_rank: Frequent Contributor
timestamp: October 12, 2015, 02:50:54 pm
content: What do you guys prefer when having your boards made?When do you use 1oz vs 2oz copper boards?

author: georges80
author_rank: Frequent Contributor
timestamp: October 12, 2015, 04:10:02 pm
content: All depends on the current that you need to handle and/or thermal issues. 1oz is the typical that most board shops will choose for you unless you specify otherwise.There''s also 0.5oz boards... Sub 1oz copper is common with multilayer boards.I've even used 4oz copper on some high current boards. You do pay a premium.There are design tools (many free, even online) that you can use to calculate resistive drops and board heating based on copper weight, track width, track length... i.e. the choice of copper weight is a design decision.cheers,george.

author: DanielS
author_rank: Frequent Contributor
timestamp: October 12, 2015, 04:11:16 pm
content: You use 1oz on moderate power boards, 2oz on high power boards, 0.5oz or less for low power stuff.The thicker the copper layer, the rougher etch patterns will be because etchant has more thickness to start eating sideways into copper under the etch resist.You need to pick your thickness depending on your application's requirements. In some case, this may mean having 1-2oz layers for ground/power planes and 0.5oz layers for fanning signals out from under a BGA.Heh, Georges beat me to posting.

author: fivefish
author_rank: Frequent Contributor
timestamp: October 13, 2015, 03:20:24 am
content: Thanks guys.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 13, 2015, 02:23:43 pm
content: FYI, 2oz is better for handmade prototypes (dead bug) -- easier to peel areas off.Also thick enough to be useful as foil, if you peel off a large patch and sand the backside to be tinnable.1oz (and thinner, say 1.0 or 0.8mm) is pretty good for building things (soldering faces together), as it's easier to solder.1oz is a good compromise for hand etched boards; 2oz takes too long, and 0.5oz is too thin. Thickness whatever works best for the purpose, of course.Tim

author: eneuro
author_rank: Super Contributor
timestamp: October 13, 2015, 09:22:03 pm
content: Quote from: georges80 on October 12, 2015, 04:10:02 pmHow powerfull were those boards and probably massive colling, since single layer 1oz = 0.0347 mm , do 5mm track has cross section area: 0.1735 mm2When we assume even 10A/mm2 than we have for this 1oz 5mm track only: 1.7A, for 4oz it will be 6.9A ~7AIt is below my standards, where custom made PCB 1oz 5mm track is reinforced withtwo 2.5mm2 copper wires in parallel soldered to 1oz track,so I have 2x2.5mm2 +0.1735 mm2 ~5.2 mm2which at 10A/mm2 gives ~51A/5mm reinforced PCB track and this is what I like for powerfull applications and 50A rated mosfetsAny good PCB track calculators to make those 4oz PCBs current capabilities estimations reliable?Probably you need massive colling and huge tracj width on those 4oz PCBs to get decent current available for hihj power applications I mean above kW, etc

author: nctnico
author_rank: Super Contributor
timestamp: October 13, 2015, 10:31:05 pm
content: I just did a 4oz board which should be able to handle 100A (dunno if I'm going to use it but that is a different story) but it turned out the online calculation tools are useless. Above 50A they just extrapolate and you get insane values.

author: Monkeh
author_rank: Super Contributor
timestamp: October 13, 2015, 10:42:47 pm
content: Quote from: eneuro on October 13, 2015, 09:22:03 pmYour numbers as ever are hilarious.Try allowing the copper to actually heat.

author: fivefish
author_rank: Frequent Contributor
timestamp: October 14, 2015, 03:15:31 am
content: My experience has been a 1oz China-made board can't handle multiple solder/desolder rework. A 2oz seems to stand this manual abuse better.But a USA-made 1oz PCB can handle multiple solder/desolder cycles just fine... of course, there is the big price difference between USA vs China made boards.

author: eneuro
author_rank: Super Contributor
timestamp: October 14, 2015, 08:38:23 am
content: Quote from: Monkeh on October 13, 2015, 10:42:47 pmI'm not designing air heaters using PCB tracks, but quite powerfull EV circuits (a few kW), so by allowing heat you decrease system efficiency it require fans or liquid cooling which is additional costs, so sometimes reinforcing 1oz PCB track with laser cut copper plate works better for me.4 layer PCB with those 2 layers insulated by 1mm PCBs inside means that this 4layer design will have much worse current capabilities than cheap double sided 1oz-2oz PCB and two of them connected mechanically in parallel in some designs

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 14, 2015, 11:21:28 am
content: This one is most correct:]http://www.smps.us/pcb-calculator.htmlIt accounts for the increased rating of traces over inner ground plane.All traces are ultimately limited by the power dissipation rating, which is quite small for a typical 10C rise. Even at 40C, this is about 43 mW/cm^2. A 1cm wide trace can dissipate 43mW/cm. At 4oz, it will have a resistance of 147 uohm/cm. Since I = sqrt(P/R), the current limit is therefore 17A (the /cm cancel out so this is independent of length).That's single sided dissipation by the way, so assumes there's a return path of the same dimensions on the back of the board, say. The current capacity goes up by about sqrt(2) if there's nothing on the back, because of conduction through the board (which is poor, but this amount of convection is even poorer, so it's okay).The calculator doesn't have 4oz, but it does give an almost exactly similar value for 3oz, which perhaps accounts for dissipation spreading laterally through the laminate as well.Which is an important point: a power board, with some temp limit, will probably have that current density flowing over a wide area, top and bottom. The calculator looks at only one trace in isolation, so already gives optimistic values compared to typical cases.Ratings go through the roof if you apply just a little forced air.Tim